Comparison of the oxidative potential of primary (POA) and secondary (SOA) organic aerosols derived from α-pinene and gasoline engine exhaust precursors

Christopher Lovett; Mohamad Baasiri; Khairallah Atwi; Mohammad H. Sowlat; Farimah Shirmohammadi; Alan L. Shihadeh; Constantinos Sioutas

doi:10.12688/f1000research.15445.1

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Research Article

Comparison of the oxidative potential of primary (POA) and secondary (SOA) organic aerosols derived from α-pinene and gasoline engine exhaust precursors

[version 1; peer review: 2 approved]

Christopher Lovett ¹, Mohamad Baasiri², Khairallah Atwi², [...] Mohammad H. Sowlat¹, Farimah Shirmohammadi¹, Alan L. Shihadeh², Constantinos Sioutas¹

Christopher Lovett ¹, Mohamad Baasiri², [...] Khairallah Atwi², Mohammad H. Sowlat¹, Farimah Shirmohammadi¹, Alan L. Shihadeh², Constantinos Sioutas¹

PUBLISHED 09 Jul 2018

Author details Author details

¹ Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, CA, 90089, USA
² Department of Mechanical Engineering, American University of Beirut, Riad El Solh, Beirut, 1107 2020, Lebanon

Christopher Lovett
Roles: Data Curation, Formal Analysis, Investigation, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Mohamad Baasiri
Roles: Formal Analysis, Investigation, Methodology, Writing – Original Draft Preparation

Khairallah Atwi
Roles: Formal Analysis, Investigation, Methodology

Mohammad H. Sowlat
Roles: Formal Analysis, Investigation, Validation, Writing – Review & Editing

Farimah Shirmohammadi
Roles: Investigation, Validation, Writing – Review & Editing

Alan L. Shihadeh
Roles: Conceptualization, Funding Acquisition, Investigation, Project Administration, Resources, Supervision, Writing – Review & Editing

Constantinos Sioutas
Roles: Conceptualization, Formal Analysis, Funding Acquisition, Investigation, Methodology, Project Administration, Resources, Supervision, Writing – Review & Editing

OPEN PEER REVIEW

REVIEWER STATUS

Abstract

Background: Primary (POA) and secondary (SOA) organic aerosols, deriving from both anthropogenic and biogenic sources, represent a major fraction of ambient particulate matter (PM) and play an important role in the etiology of respiratory and cardiovascular diseases, largely through systemic inflammation and cellular oxidative stress. The relative contributions of these species to the inhalation burden, however, are rather poorly characterized. In this study, we measured the in vitro oxidative stress response of alveolar macrophages exposed to primary and secondary PM derived from both anthropogenic and biogenic sources.
Methods: POA and SOA were generated within an oxidation flow reactor (OFR) fed by pure, aerosolized α-pinene or gasoline engine exhaust, as representative emissions of biogenic and anthropogenic sources, respectively. The OFR utilized an ultraviolet (UV) lamp to achieve an equivalent atmospheric aging process of several days.
Results: Anthropogenic SOA produced the greatest oxidative response (1900 ± 255 µg-Zymosan/mg-PM), followed by biogenic (α-pinene) SOA (1321 ± 542 µg-Zymosan/mg-PM), while anthropogenic POA produced the smallest response (51.4 ± 64.3 µg-Zymosan/mg-PM).
Conclusions: These findings emphasize the importance of monitoring and controlling anthropogenic emissions in the urban atmosphere, while also taking into consideration spatial and seasonal differences in SOA composition. Local concentrations of biogenic and anthropogenic species contributing to the oxidative potential of ambient PM may vary widely, depending on the given region and time of year, due to factors such as surrounding vegetation, proximity to urban areas, and hours of daylight.

Keywords

Particulate Matter, SOA, Biogenic PM, Anthropogenic PM, Photochemical Aging

Corresponding author: Christopher Lovett

Competing interests: No competing interests were disclosed.

Grant information: This study was supported in part by the University of Southern California Viterbi Dean’s Ph.D. Fellowship, and by National Institutes of Health research grants [RF1-AG051521-01 and R21-AG050201-01A1].
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Copyright: © 2018 Lovett C et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Data associated with the article are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

How to cite: Lovett C, Baasiri M, Atwi K et al. Comparison of the oxidative potential of primary (POA) and secondary (SOA) organic aerosols derived from α-pinene and gasoline engine exhaust precursors [version 1; peer review: 2 approved]. F1000Research 2018, 7:1031 (https://doi.org/10.12688/f1000research.15445.1) First published: 09 Jul 2018, 7:1031 (https://doi.org/10.12688/f1000research.15445.1) Latest published: 11 Mar 2019, 7:1031 (https://doi.org/10.12688/f1000research.15445.2)

Introduction

A large fraction of ambient particulate matter (PM) in the urban atmosphere consists of a mixture of primary organic aerosols (POA), derived from anthropogenic and biogenic PM sources, as well as secondary organic aerosols (SOA) produced during the photo-oxidation of both types of POA (Baltensperger et al., 2005; Després et al., 2012). Urban PM can consist of up to 90% SOA, the majority originating from primary biogenic aerosols, including the monoterpene α-pinene, one of the largest components of primary biogenic PM worldwide (Hallquist et al., 2009; Seinfeld & Pankow, 2003).

Several human health problems linked to ambient PM, including asthma, cardiovascular disease, and heart failure (Delfino et al., 2005; Dominici et al., 2006; Kim et al., 2013; Shah et al., 2013), are mediated largely by the cellular inflammatory response, including reactive oxygen species (ROS) formation (Li et al., 2003; Ray et al., 2012). Research investigating PM health effects has mostly focused on primary emissions, while studies of secondary PM effects are not as common. Some studies, however, report that both anthropogenic (Decesari et al., 2017; Saffari et al., 2015; Verma et al., 2014; Verma et al., 2015a; Verma et al., 2015b) and biogenic (Baltensperger et al., 2008; Gaschen et al., 2010; Rohr, 2013) SOA elicit greater adverse health effects than POA precursors.

In this study, we investigate the effects of photochemical oxidation on the oxidative potential of biogenic and anthropogenic PM. Samples of each PM type were collected before and after photochemical aging within a laboratory reaction chamber equipped with an ultraviolet lamp. The in vitro alveolar macrophage (AM) assay was used to quantify PM oxidative potential (Landreman et al., 2008; Li et al., 2008; Shafer et al., 2010).

Methods

Sampling methods

Photochemical oxidation of primary emissions occurred within a 64-liter stainless steel oxidation flow reactor (OFR) equipped with a single UV lamp (BHK Analamp, Model No. 82-9304-03) emitting radiation at 185 and 254 nm. Upstream of the PM sources, inlet air first passed through an activated carbon denuder and high-efficiency particulate air (HEPA) filter to remove all particles. Within the OFR, a warm, humid environment (22°C/60% RH) was maintained, allowing H₂O to act as a source of hydroxyl radicals in the UV-catalyzed oxidation reactions, which resulted in SOA formation.

The biogenic sampling setup is depicted in Figure 1. Particle-free inlet air was introduced at a flow rate of 25 lpm. 0.5 lpm of this incoming air stream was diverted into a 250 ml Büchner flask containing a 15-ml glass vial of pure, reagent grade α-pinene. Three small holes in the vial cap allowed for diffusion of α-pinene vapors into the flask. The remaining 24.5 lpm flow of particle-free air proceeded through a humidifier (heated flask containing distilled water) and into the reactor, where it mixed with the α-pinene vapors, resulting in a dilution ratio of 50:1.

Figure 1. Biogenic (α-pinene) particulate matter (PM) sampling setup.

The anthropogenic sampling setup is depicted in Figure 2. Exhaust from a four-stroke single cylinder gasoline generator (Honda SHX1000, 49cc displacement, 8.0:1 compression ratio, operating at 3000 RPM) was drawn through a rotating disk dilutor (RDD; Testo Engineering, MD19-3E) operating at a dilution ratio of 50:1. 5 lpm of the diluted engine exhaust was diverted into the reaction chamber, where it mixed with 20 lpm of humidified, particle-fee air, resulting in a total dilution ratio of 250:1.

Figure 2. Anthropogenic (gasoline engine exhaust) particulate matter (PM) sampling setup.

Particles were collected downstream of the reaction chamber on Teflon and quartz filters. In the POA condition, PM was collected as the α-pinene or engine emissions passed through a dark OFR. In the SOA condition, the aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.

Filter conditioning

Prior to sampling, quartz filters were baked in a furnace oven at 500°C for 5 hours. Teflon filters were conditioned for 24 hours in a controlled environment (23°C and 46% relative humidity) before weighing. Teflon filters were weighed before and after sampling to determine the mass collected with an MT5 Microbalance (Mettler-Toledo Inc., Columbus, OH, USA). Mass collected on quartz filters was calculated based on the aerosol concentration (from Teflon filters) and sampling flow rate. After sampling, all filters were placed in petri dishes lined with baked aluminum foil, sealed with Teflon tape, and stored in a refrigerated environment until analysis.

Laboratory analyses

Quartz filters were analyzed for elemental carbon (EC) and organic carbon (OC) content by the National Institute for Occupational Safety and Health (NIOSH) Thermal Optical Transmission (TOT) Method 5040, using a flame ionization detector (FID) to quantify evolved carbon as CH₄ (Birch & Cary, 1996; Peterson & Richards, 2002).

The alveolar macrophage (AM) in vitro assay was used to determine the oxidative potential of the Teflon filter PM samples. Alveolar macrophages obtained from the American Type Culture Collection (cell line NR8383, RRID: CVCL_4396) were maintained in Ham’s F12 medium (#11765-047, ThermoFisher, Waltham, MA, USA) supplemented with 2mM L-glutamine (GlutaMAX; #31765-035, ThermoFisher, Waltham, MA, USA), 1.176 g/L sodium bicarbonate, and 15% heat inactivated fetal bovine serum (FBS; #45000-734, VWR, Radnor, PA, USA). Cells were cultured in flasks and kept in an incubator at 37°C/5% CO₂. Non-adherent cells were transferred to new flasks weekly. A floating cell concentration of approximately 4 × 10⁵ cells/mL media was maintained. The macrophage cells were exposed to each type of PM sample for 2.5 hours, using 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA) as a fluorescent probe to quantify the cellular formation of oxidative species. The non-fluorescent DCFH-DA acts by entering the cell, where it is de-acetylated by cellular enzymes to yield 2,7-dichlorodihydrofluorescein (DCFH), also non-fluorescent. DCFH is then oxidized by reactive species, generated during the cellular oxidative stress response to PM exposure, to form the highly fluorescent and detectable 2,7-dichlorofluorescein (DCF), which was quantified spectrophotometrically with a CytoFlour II automated fluorescence plate reader (PerSeptive Biosystems, Framingham, MA, USA) (Landreman et al., 2008; Shafer et al., 2010).

Results

EC/OC results are presented in Figure 3. EC was most abundant in engine POA (0.081 μg-EC/μg-PM), with no significant amount present in either engine or α-pinene SOA. Mass fractions of OC were higher than EC in all conditions (engine POA: 0.62 μg-OC/μg-PM, engine SOA: 0.54 μg-OC/μg-PM, α-pinene SOA: 0.54 μg-OC/μg-PM). Figure 4 presents oxidative potential results on a mass-fraction basis, standardized to Zymosan units (μg-Zymosan units/mg-PM). Mass fraction results reveal how the intrinsic PM toxicity as indexed by oxidative potential changes over time due to photochemical aging. The measured oxidative potential for engine POA was 51.4 (± 64.3) µg-Zymosan/mg-PM, and for engine SOA it was 1900 (± 255) µg-Zymosan/mg-PM, while for α-pinene SOA, the result was 1321 (± 542) µg-Zymosan/mg-PM (pure α-pinene was not assayed).

Figure 3. Mass fractions of elemental carbon (EC) and organic carbon (OC) in engine primary organic aerosol (POA) and engine & α-pinene secondary organic aerosols (SOA).

Error bars represent laboratory uncertainty values based on contributions of analytical error (standard deviation) and blank subtraction (standard deviation of at least three method blanks).

Figure 4. Mass-fraction based oxidative potential: Engine primary organic aerosol (POA) and engine & α-pinene secondary organic aerosols (SOA).

Error bars represent laboratory uncertainty values based on contributions of analytical error (standard deviation) and blank subtraction (standard deviation of at least three method blanks).

Elemental Carbon - Organic Carbon (EC/OC) Final Report

Project:	Beirut POA/SOA
COC Date:	4/26/2017	Received Date:	5/10/2017			Analysis Date:	6/7/2017	Report Date:	6/15/2017

	Sample Type:	47 mm Quartz Filter		Exposed Sample Area: 10.18 cm2			Area Used for EC/OC Analysis: 0.50 cm2


Submitter Sample Description	Submitter Filter ID	Organic Carbon (OC) µg/filter		Elemental Carbon (EC) µg/filter		Total Carbon (TC) µg/filter		Pyrolytic Carbon (PC) µg/filter
		Value	Uncertainty	Value	Uncertainty	Value	Uncertainty	Value
Engine Exhaust SOA	17041815-Q	3822	192	24.1	16.5	3846	194	296
Engine Exhaust SOA	17041817-Q	5820	292	45.5	28.1	5865	295	507
Engine Exhaust SOA	17041820-Q	4803	241	46.1	22.4	4850	245	392
Engine Exhaust SOA	170706A-Q	2431.8	122.6	6.3	7.27	2438.1	123.8	129.41
Engine Exhaust SOA	170707A-Q	3320.8	167	0	10.28	3320.8	168	195.91
Engine Exhaust SOA	170624A-Q	4007.4	201.3	27.01	26.44	4034.4	203.6	492.14
Engine Exhaust POA	170926-Q	449.1	23.53	57.73	2.28	506.83	27.49	-22.86
α-pinene SOA	171024-Q	239.54	14.37	0	0.98	239.54	15.56	7.57
α-pinene SOA	171025-Q	259.66	15.37	0	1.13	259.66	16.57	10.67
BLANK		5.77	1.09	0	0.42	5.77	1.9	0.41

Notes:
Results reported per FULL filter
µg/filter results have not been blank subtracted
0 indicates a non-detect, NA indicates the result is not available

Dataset 1.Figure 3 EC-OC Raw Data.

Macrophage ROS Assay

USC_Beirut POA/SOA Study

Substrate Type:	Teflon 47 mm filters

																				Use These Values
											UT/ZYM Slope =		0.1278			Blank Has NOT Been Applied				All data sensitivity normalized to UT prior to ZYM calibration
									Fluorescence Units (FU)							Fluorescence Units (FU)		Fluorescence Units / Filter		µg Zymosan Units / Filter		µg PM per filter	µg Zymosan Units / mg PM
									Sample ROS		UT ROS					ROS Response Corrected For Blank		ROS Response Corrected For Dilution & Filter Fraction		ROS Response Corrected For Dilution & Filter Fraction			ROS Response Corrected For Dilution & Filter Fraction
	ROS Run Date	Submitter Sample ID	ROS Dilution Series	WSLH Sample ID	Plate Number	ROS Protocol	Extract Treatment	Filter Fraction Analyzed	UT-Corrected		Raw		ROS Volume (mL)	Extraction Volume (mL)	Dilution Factor
					of ROS Run				Value (FU)	Stdev	Value (FU)	Stdev				Value	Stdev	Value	Stdev	Value	Stdev		Value	Stdev	Sample

a-Pinene SOA	2-Jun-17	17041809-T	0.0635, 0.127, 0.254, 0.508	a-Pinene SOA-09	1	488/530/515	Not Filtered	0.5	1169	103	1,003	2	0.1	1.5	1	1169	103	35,070	3090	447	43	812.1	550.4	53	17041809-T	a-Pinene SOA
a-Pinene SOA	13-Jun-17	17041811-T	0.03175, 0.0635, 0.127, 0.254, 0.508	a-Pinene SOA-11	1	488/530/515	Not Filtered	0.5	2686	159	628	12	0.1	1.5	1	2686	159	80,580	4770	1640	116	1143.3	1434	101.7	17041811-T	a-Pinene SOA
a-Pinene SOA	13-Jun-17	17041812-T	0.03175, 0.0635, 0.127, 0.254, 0.508	a-Pinene SOA-12	1	488/530/515	Not Filtered	0.5	1268	32	704	7	0.1	1.5	1	1268	32	38,040	960	691	32	614.4	1125	52.2	17041812-T	a-Pinene SOA
Eng SOA	13-Jun-17	17041815-T	0.0079375, 0.015875, 0.03175, 0.0635, 0.127, 0.254	Engine Exhaust SOA-15	1	488/530/515	Not Filtered	0.25	6304	269	677	11	0.1	1.5	1	6304	269	378,240	16140	7147	413	3283.7	2177	125.8	17041815-T	Eng SOA
Eng SOA	2-Jun-17	17041817-T	0.03175, 0.0635, 0.127, 0.254	Engine Exhaust SOA-17	2	488/530/515	Not Filtered	0.258	2245	95	903	8	0.1	1.5	1	2245	95	130,645	5528	1849	106	4467.3	413.9	23.8	17041817-T	Eng SOA
Eng SOA	2-Jun-17	17041820-T	0.03175, 0.0635, 0.127, 0.254	Engine Exhaust SOA-20	2	488/530/515	Not Filtered	0.25	2047	117	809	25	0.1	1.5	1	2047	117	122,820	7020	1942	134	3637.8	533.8	36.9	17041820-T	Eng SOA
Eng POA	13-Jun-17	Eng POA Composite:	0.127, 0.254, 0.508, 1.000	Eng POA Composite:	1	488/530/515	Not Filtered	0.5	8	10	611	1	0.1	1.5	1	8	10	240	300	5	6	97.7	51.4	64.3	Eng POA Composite:	Eng POA
		170418-022-T -023-T -024-T		170418-022-T -023-T -024-T																					170418-022-T -023-T -024-T
Eng SOA	28-Jul-17	170706a-T	0.015875, 0.03175, 0.0635, 0.127	Eng SOA	2	488/530/515	Not Filtered	0.5	6609	329	696	19	0.1	2	1	6609	329	264,372	13168	4697	275	2.3317	2014	118	170706a-T	Eng SOA
Eng SOA	28-Jul-17	170707a-T	0.0079375, 0.015875, 0.03175, 0.0635	Eng SOA	2	488/530/515	Not Filtered	0.5	7348	1254	659	8	0.1	2	1	7348	1254	293,916	50170	5515	957	3.484	1583	275	170707a-T	Eng SOA
Eng SOA	28-Jul-17	170624a-T	0.015875, 0.03175, 0.0635, 0.127	Eng SOA	2	488/530/515	Not Filtered	0.5	5446	1292	655	16	0.1	2	1	5446	1292	217,842	51698	4112	984	2.2496	1828	437	170624a-T	Eng SOA
a-Pinene SOA	28-Jul-17	170625-T	0.015875, 0.03175, 0.0635, 0.127	a-Pinene SOA	2	488/530/515	Not Filtered	1	3218	178	661	28	0.1	2	1	3218	178	64,368	3561	1205	76	0.8243	1462	93	170625-T	a-Pinene SOA
a-Pinene SOA	21-Jul-17	170627-T	0.0635, 0.127, 0.254, 0.508	a-Pinene SOA	3	488/530/515	Not Filtered	1	10784	180	682	2	0.1	2	1	10784	180	215,670	3592	3912	137	1.9232	2034	71	170627-T	a-Pinene SOA
	Blank Summary
	2-Jun-17	Method Blank	0.508, 1.00		1	488/530/515	Not Filtered	1	41	14	1,020	12	0.1	1.5
	21-Jul-17	7-21-17 Method Blank	0.508, 1.00		1	488/530/515	Not Filtered	1	3	4	870	37	0.1	2
	28-Jul-17	7-21-17 Method Blank	1		1	488/530/515	Not Filtered	1	57	32	718	30	0.1	2

			Quality Assurance - Quality Control Sample Outcome Summary												METHOD BLANK SUMMARY
															Blank	41	14


		ZYMOSAN POSITIVE CONTROL				Zymosan Positive Control
		Row A & 2nd Row				Value	St Dev	Slope	St Dev	RSD
		2-Jun-17	12/13/16 "B" 100% Zym - 0.1mg/ml		Plate 1	5129	135	51290	1350	0.026
		2-Jun-17	12/13/16 "B" 100% Zym - 0.1mg/ml		Plate 1	5260	37	52600	370	0.007
		2-Jun-17	12/13/16 "B" 100% Zym - 0.1mg/ml		Plate 2	4753	110	47530	1100	0.023
		2-Jun-17	12/13/16 "B" 100% Zym - 0.1mg/ml		Plate 2	4814	295	48140	2950	0.061
		13-Jun-17	12/13/16 "B" 100% Zym - 0.1mg/ml		Plate 1	4063	366	40630	3660	0.09
		13-Jun-17	12/13/16 "B" 100% Zym - 0.1mg/ml		Plate 1	3591	94	35910	940	0.026
						4602	647	14.1		0.039	MEAN
						MEAN	STDEV	RSD%		0.031	STDEV

		SUPPLEMENTAL SRM				Urban Dust
		Urban Dust				Value	St Dev	RSD
		2-Jun-17	12/12/16 Urban Dust		Plate 1	8397	66	0.008
		2-Jun-17	12/12/16 Urban Dust		Plate 2	7166	154	0.021
		13-Jun-17	12/12/16 Urban Dust		Plate 1	12605	44	0.003
						9389	2852	30.4
						MEAN	STDEV	RSD%

		SUPPLEMENTAL SRM				Z088D6
		Z088D6				Value	St Dev	RSD
		2-Jun-17	12/12/16 Z088D6		Plate 1	6338	220	0.035
		2-Jun-17	12/12/16 Z088D6		Plate 2	6042	103	0.017
		13-Jun-17	12/12/16 Z088D6		Plate 1	6277	87	0.014
						6219	156	2.5
						MEAN	STDEV	RSD%

		SUPPLEMENTAL SRM				Pyocyanin
		Pyocyanin (7/12/16)				Value	St Dev	RSD
		2-Jun-17	0.625 µg/mL		Plate 1	1475	102	0.069
		2-Jun-17	0.625 µg/mL		Plate 2	1588	27	0.017
		13-Jun-17	0.625 µg/mL		Plate 1	1046	32	0.031
						1370	286	20.9
						MEAN	STDEV	RSD%


		Quality Assurance - Quality Control Sample Outcome Summary											METHOD BLANK SUMMARY
													Blank	29.9	38.3
		ZYMOSAN POSITIVE CONTROL				Zymosan Positive Control
		Row A & 2nd Row				Value	St Dev	Slope	St Dev	RSD
		21-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 1	4141	16	41410	161	0.004
		21-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 1	4410	28	44098	277	0.006
		21-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 2	3996	117	39964	1175	0.029
		21-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 2	4055	106	40547	1063	0.026
		21-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 3	3961	145	39614	1448	0.037
		21-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 3	3744	94	37443	936	0.025
		28-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 1	3963	238	39630	2382	0.06
		28-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 1	4052	144	40520	1439	0.036
		28-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 2	3814	284	38143	2843	0.075
		28-Jul-17	4/14/17 "A" 100% Zym - 0.1mg/ml		Plate 2	3872	39	38720	385	0.01
						4001	186	4.7		0.031	MEAN
						MEAN	STDEV	RSD%		0.023	STDEV


		SUPPLEMENTAL SRM				Urban Dust
		Urban Dust				Value	St Dev	RSD
		21-Jul-17	12/12/16 Urban Dust		Plate 1	9793	139	0.014
		21-Jul-17	12/12/16 Urban Dust		Plate 2	8701	47	0.005
		21-Jul-17	12/12/16 Urban Dust		Plate 3	7567	164	0.022
		28-Jul-17	12/12/16 Urban Dust		Plate 1	9667	973	0.101
		28-Jul-17	12/12/16 Urban Dust		Plate 2	9278	55	0.006
						9001	908	10.1
						MEAN	STDEV	RSD%

		SUPPLEMENTAL SRM				Z088D6
		Z088D6				Value	St Dev	RSD
		21-Jul-17	12/12/16 Z088D6		Plate 1	6263	187	0.03
		21-Jul-17	12/12/16 Z088D6		Plate 2	5626	167	0.03
		21-Jul-17	12/12/16 Z088D6		Plate 3	5546	85	0.015
		28-Jul-17	12/12/16 Z088D6		Plate 1	6343	162	0.026
		28-Jul-17	12/12/16 Z088D6		Plate 2	6624	190	0.029
						6080	472	7.8
						MEAN	STDEV	RSD%

		SUPPLEMENTAL SRM				Pyocyanin
		Pyocyanin				Value	St Dev	RSD
		21-Jul-17	7/12/16 0.625 µg/mL		Plate 1	1457	46	0.031
		21-Jul-17	7/12/16 0.625 µg/mL		Plate 2	1398	21	0.015
		21-Jul-17	7/12/16 0.625 µg/mL		Plate 3	1395	13	0.009
		28-Jul-17	7/12/16 0.625 µg/mL		Plate 1	1062	66	0.063
		28-Jul-17	7/12/16 0.625 µg/mL		Plate 2	1039	53	0.051
						1270	202	15.9

Dataset 2.Figure 4 ROS Raw Data.

Summary and conclusions

The findings of the current reaction chamber study indicate that both anthropogenic and biogenic SOA induce greater cellular oxidative stress than primary engine exhaust. This effect was found to be largest in response to engine exhaust SOA, thus implicating anthropogenic as the major contributor to adverse human health effects in urban environments, though the contribution of biogenic SOA can be quite significant in some geographical areas. Atmospheric aging of PM increases its intrinsic oxidative potential many fold, and thus photochemistry in a region that experiences abundant sunshine, long days, and/or stagnation of circulating air due to an inversion layer or some other reason, may increase the toxicity of PM over time.

Data availability

The following raw data sets are provided as comma separated values (.csv) files:

Dataset 1: Figure 3 EC-OC Raw Data 10.5256/f1000research.15445.d209280 (Lovett et al., 2018a)

Dataset 2: Figure 4 ROS Raw Data 10.5256/f1000research.15445.d209281 (Lovett et al., 2018b)

Competing interests

No competing interests were disclosed.

Grant information

The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Faculty Opinions recommended

References

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Baltensperger U, Kalberer M, Dommen J, et al.: Secondary organic aerosols from anthropogenic and biogenic precursors. Faraday Discuss. 2005; 130: 265–278; discussion 363–86, 519–24. PubMed Abstract | Publisher Full Text
Birch ME, Cary RA: Elemental carbon-based method for monitoring occupational exposures to particulate diesel exhaust. Aerosol Sci Technol. 1996; 25(3): 221–241. Publisher Full Text
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Lovett C, Baasiri M, Atwi K, et al.: Dataset 1 in: Comparison of the oxidative potential of primary (POA) and secondary organic aerosols (SOA) derived from α-pinene and gasoline engine exhaust precursors. F1000Research. 2018a. Data Source
Lovett C, Baasiri M, Atwi K, et al.: Dataset 2 in: Comparison of the oxidative potential of primary (POA) and secondary organic aerosols (SOA) derived from α-pinene and gasoline engine exhaust precursors. F1000Research. 2018b. Data Source
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Version 2

VERSION 2 PUBLISHED 09 Jul 2018

Author details Author details

Christopher Lovett
Roles: Data Curation, Formal Analysis, Investigation, Validation, Writing – Original Draft Preparation, Writing – Review & Editing

Mohamad Baasiri
Roles: Formal Analysis, Investigation, Methodology, Writing – Original Draft Preparation

Khairallah Atwi
Roles: Formal Analysis, Investigation, Methodology

Mohammad H. Sowlat
Roles: Formal Analysis, Investigation, Validation, Writing – Review & Editing

Farimah Shirmohammadi
Roles: Investigation, Validation, Writing – Review & Editing

Alan L. Shihadeh
Roles: Conceptualization, Funding Acquisition, Investigation, Project Administration, Resources, Supervision, Writing – Review & Editing

Constantinos Sioutas
Roles: Conceptualization, Formal Analysis, Funding Acquisition, Investigation, Methodology, Project Administration, Resources, Supervision, Writing – Review & Editing

Competing interests

No competing interests were disclosed.

Grant information

This study was supported in part by the University of Southern California Viterbi Dean’s Ph.D. Fellowship, and by National Institutes of Health research grants [RF1-AG051521-01 and R21-AG050201-01A1].
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Article Versions (2)

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Published: 11 Mar 2019, 7:1031

https://doi.org/10.12688/f1000research.15445.2

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Published: 09 Jul 2018, 7:1031

https://doi.org/10.12688/f1000research.15445.1

© 2018 Lovett C et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Data associated with the article are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).

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Lovett C, Baasiri M, Atwi K et al. Comparison of the oxidative potential of primary (POA) and secondary (SOA) organic aerosols derived from α-pinene and gasoline engine exhaust precursors [version 1; peer review: 2 approved] F1000Research 2018, 7:1031 (https://doi.org/10.12688/f1000research.15445.1)

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Version 1

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Reviewer Report 25 Feb 2019

Zhi Ning, Division of Environment and Sustainability, Hong Kong University of Science & Technology, Hong Kong, China

Approved

https://doi.org/10.5256/f1000research.16832.r43635

General Comments:

The authors have investigated the oxidative potential of POA and SOA from two different sources namely alpha-pinene and gasoline engine exhaust. The experimental setup included an UV chamber (oxidation flow reactor), to mimic the sun light’s UV rays, to compare primary and secondary organic aerosol-induced radical generation under light and in dark. The comparison could contribute great value to the manuscript if additional parameters as listed below are included in it:

Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. In some experiments, where UV rays are used to excite the organic aerosols, the elicitation of superoxide radicals is also possible.
Page 3: Right column: Lines 28-30: The statement “aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.” is not clear. Does that mean the whole sample streaming is done for a continuous 90 minutes? Was it the same for the aerosol sampling done in dark OFR?
Page 3: Right column: Line 33: The information of the control sample needs to be included here.
Page 4: Left column: Line 23: The analysis part has some information missing such as incubation time for cell growth, and are the same generation (life cycle) used for analysis?
Page 4: Left column: Line 25: The cell exposure study has some basic information missing - PM dose, route of exposure (directly on filters or on PM extracts), number of times analysed (duplicate or triplicate). Please include for clarity.
Page 5: Figure 4: The biogenic organic compounds (for example: the alpha-pinene) are believed to be more hydrophilic compared to engine exhaust organics. Please include a discussion if the water solubility of samples is also driving the difference in oxidative stress.

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests: No competing interests were disclosed.

Reviewer Expertise: Particle induced cellular oxidative stress, sensor development and application

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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Report a concern

Author Response 05 Mar 2019

Christopher Lovett, Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, 90089, USA

05 Mar 2019

Author Response

Authors’ responses to specific comments of Dr. Zhi Ning:

Comment 1: Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. ... Continue reading Authors’ responses to specific comments of Dr. Zhi Ning:

Comment 1: Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. In some experiments, where UV rays are used to excite the organic aerosols, the elicitation of superoxide radicals is also possible.

Text Added:
“While the production of superoxide radicals is possible, the major products of H₂O oxidation generated in this type of OFR are hydroxyl radicals, especially at less than 80% relative humidity (Seinfeld & Pandis, 2016; Kamens et al., 2011; Jang et al., 2002).”

Comment 2: Page 3: Right column: Lines 28-30: The statement “aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.” is not clear. Does that mean the whole sample streaming is done for a continuous 90 minutes? Was it the same for the aerosol sampling done in dark OFR?

Text Revision:
“In the SOA condition, the aerosol stream was sampled while the UV lamp inside the reactor was on. During this condition, the sample stream was diverted for the first 90 minutes to ensure that the reactor was operating under steady-state conditions while samples were collected.”

Comment 3: Page 3: Right column: Line 33: The information of the control sample needs to be included here.

Authors’ Response:
The only control samples were the filter blanks submitted to the laboratory for chemical and toxicological analyses as discussed in Section 2.3. Discussion of the control condition utilized in the macrophage assay (untreated cells) is included in the response to Comment 5.

Comment 4: Page 4: Left column: Line 23: The analysis part has some information missing such as incubation time for cell growth, and are the same generation (life cycle) used for analysis?

Text Added:
“In preparation for PM exposures, the non-adherent fraction of macrophage cells was harvested from flasks and concentrated by centrifugation (750 RPM) for 5 minutes. The culture medium was removed, and the cell suspension was diluted to a concentration of 1,000 cells/μL. 100 μL aliquots of these suspended cells were then pipetted into each well of 96-well plates (100,000 cells/well) and incubated at 37°C/5% CO₂ for 2 hours. Following the 2-hour incubation period, nearly all macrophages were adhered to each well bottom. During PM treatments, supernatant media was aspirated and replaced with 100 μL of sample extract or blank control solution in each well.”

Comment 5: Page 4: Left column: Line 25: The cell exposure study has some basic information missing - PM dose, route of exposure (directly on filters or on PM extracts), number of times analysed (duplicate or triplicate). Please include for clarity.

Text Added:
“Each Teflon filter (PM sample or blank) was divided into two sections, one for the macrophage assay and one for chemical analysis. The filter halves used for the cell assay underwent sonication in 900 μL of purified water for approximately 16 hours at room temperature to extract the water-soluble components. These filters were then removed from the aqueous extracts, and 10x concentrated salts-glucose medium (SGM) was added to create buffered PM extract solutions for use in the PM treatments.”“Each treatment or control was run in triplicate (3 wells each). Additionally, several untreated and method blank controls were included on each 96-well plate. Zymosan was included as a positive control at a concentration of 0.125 mg-zymosan/mL in a buffered SGM solution. Results are reported as the increase in fluorescence due to sample treatments relative to the fluorescence observed in the untreated control condition.”

Comment 6: Page 5: Figure 4: The biogenic organic compounds (for example: the alpha-pinene) are believed to be more hydrophilic compared to engine exhaust organics. Please include a discussion if the water solubility of samples is also driving the difference in oxidative stress.

Text Added (to Summary and Conclusions):
“While the macrophage assay is generally more sensitive to water-soluble components of PM, as compared to non-polar PM species, the large cellular oxidative stress response to SOA, especially anthropogenic SOA, cannot be attributed entirely to hydrophilicity. Biogenic organic compounds are generally more hydrophilic than organic products of anthropogenic processes such as combustion, yet greater ROS activity in response to anthropogenic PM was observed. The alveolar macrophage assay is considered an excellent model of inhalation toxicity, and increased ROS formation reliably indexes greater toxicity, whether ultimately due to increased bioavailability of harmful molecules or simply greater quantities of harmful PM species (Landreman et al., 2008). Thus, the results of this study clearly indicate that oxidized PM species, whether of biogenic or anthropogenic origin, are more toxic that primary PM, regardless of water-solubility, with the greatest toxicity resulting from anthropogenic SOA exposures.”
Authors’ responses to specific comments of Dr. Zhi Ning:

Comment 1: Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. In some experiments, where UV rays are used to excite the organic aerosols, the elicitation of superoxide radicals is also possible.

Text Added:
“While the production of superoxide radicals is possible, the major products of H₂O oxidation generated in this type of OFR are hydroxyl radicals, especially at less than 80% relative humidity (Seinfeld & Pandis, 2016; Kamens et al., 2011; Jang et al., 2002).”

Comment 2: Page 3: Right column: Lines 28-30: The statement “aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.” is not clear. Does that mean the whole sample streaming is done for a continuous 90 minutes? Was it the same for the aerosol sampling done in dark OFR?

Text Revision:
“In the SOA condition, the aerosol stream was sampled while the UV lamp inside the reactor was on. During this condition, the sample stream was diverted for the first 90 minutes to ensure that the reactor was operating under steady-state conditions while samples were collected.”

Comment 3: Page 3: Right column: Line 33: The information of the control sample needs to be included here.

Authors’ Response:
The only control samples were the filter blanks submitted to the laboratory for chemical and toxicological analyses as discussed in Section 2.3. Discussion of the control condition utilized in the macrophage assay (untreated cells) is included in the response to Comment 5.

Comment 4: Page 4: Left column: Line 23: The analysis part has some information missing such as incubation time for cell growth, and are the same generation (life cycle) used for analysis?

Text Added:
“In preparation for PM exposures, the non-adherent fraction of macrophage cells was harvested from flasks and concentrated by centrifugation (750 RPM) for 5 minutes. The culture medium was removed, and the cell suspension was diluted to a concentration of 1,000 cells/μL. 100 μL aliquots of these suspended cells were then pipetted into each well of 96-well plates (100,000 cells/well) and incubated at 37°C/5% CO₂ for 2 hours. Following the 2-hour incubation period, nearly all macrophages were adhered to each well bottom. During PM treatments, supernatant media was aspirated and replaced with 100 μL of sample extract or blank control solution in each well.”

Comment 5: Page 4: Left column: Line 25: The cell exposure study has some basic information missing - PM dose, route of exposure (directly on filters or on PM extracts), number of times analysed (duplicate or triplicate). Please include for clarity.

Text Added:
“Each Teflon filter (PM sample or blank) was divided into two sections, one for the macrophage assay and one for chemical analysis. The filter halves used for the cell assay underwent sonication in 900 μL of purified water for approximately 16 hours at room temperature to extract the water-soluble components. These filters were then removed from the aqueous extracts, and 10x concentrated salts-glucose medium (SGM) was added to create buffered PM extract solutions for use in the PM treatments.”“Each treatment or control was run in triplicate (3 wells each). Additionally, several untreated and method blank controls were included on each 96-well plate. Zymosan was included as a positive control at a concentration of 0.125 mg-zymosan/mL in a buffered SGM solution. Results are reported as the increase in fluorescence due to sample treatments relative to the fluorescence observed in the untreated control condition.”

Comment 6: Page 5: Figure 4: The biogenic organic compounds (for example: the alpha-pinene) are believed to be more hydrophilic compared to engine exhaust organics. Please include a discussion if the water solubility of samples is also driving the difference in oxidative stress.

Text Added (to Summary and Conclusions):
“While the macrophage assay is generally more sensitive to water-soluble components of PM, as compared to non-polar PM species, the large cellular oxidative stress response to SOA, especially anthropogenic SOA, cannot be attributed entirely to hydrophilicity. Biogenic organic compounds are generally more hydrophilic than organic products of anthropogenic processes such as combustion, yet greater ROS activity in response to anthropogenic PM was observed. The alveolar macrophage assay is considered an excellent model of inhalation toxicity, and increased ROS formation reliably indexes greater toxicity, whether ultimately due to increased bioavailability of harmful molecules or simply greater quantities of harmful PM species (Landreman et al., 2008). Thus, the results of this study clearly indicate that oxidized PM species, whether of biogenic or anthropogenic origin, are more toxic that primary PM, regardless of water-solubility, with the greatest toxicity resulting from anthropogenic SOA exposures.”
Competing Interests: No competing interests. Close
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Respond or Comment

COMMENTS ON THIS REPORT

Author Response 05 Mar 2019

Christopher Lovett, Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, 90089, USA

05 Mar 2019

Author Response

Authors’ responses to specific comments of Dr. Zhi Ning:

Comment 1: Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. ... Continue reading Authors’ responses to specific comments of Dr. Zhi Ning:

Comment 1: Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. In some experiments, where UV rays are used to excite the organic aerosols, the elicitation of superoxide radicals is also possible.

Text Added:
“While the production of superoxide radicals is possible, the major products of H₂O oxidation generated in this type of OFR are hydroxyl radicals, especially at less than 80% relative humidity (Seinfeld & Pandis, 2016; Kamens et al., 2011; Jang et al., 2002).”

Comment 2: Page 3: Right column: Lines 28-30: The statement “aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.” is not clear. Does that mean the whole sample streaming is done for a continuous 90 minutes? Was it the same for the aerosol sampling done in dark OFR?

Text Revision:
“In the SOA condition, the aerosol stream was sampled while the UV lamp inside the reactor was on. During this condition, the sample stream was diverted for the first 90 minutes to ensure that the reactor was operating under steady-state conditions while samples were collected.”

Comment 3: Page 3: Right column: Line 33: The information of the control sample needs to be included here.

Authors’ Response:
The only control samples were the filter blanks submitted to the laboratory for chemical and toxicological analyses as discussed in Section 2.3. Discussion of the control condition utilized in the macrophage assay (untreated cells) is included in the response to Comment 5.

Comment 4: Page 4: Left column: Line 23: The analysis part has some information missing such as incubation time for cell growth, and are the same generation (life cycle) used for analysis?

Text Added:
“In preparation for PM exposures, the non-adherent fraction of macrophage cells was harvested from flasks and concentrated by centrifugation (750 RPM) for 5 minutes. The culture medium was removed, and the cell suspension was diluted to a concentration of 1,000 cells/μL. 100 μL aliquots of these suspended cells were then pipetted into each well of 96-well plates (100,000 cells/well) and incubated at 37°C/5% CO₂ for 2 hours. Following the 2-hour incubation period, nearly all macrophages were adhered to each well bottom. During PM treatments, supernatant media was aspirated and replaced with 100 μL of sample extract or blank control solution in each well.”

Comment 5: Page 4: Left column: Line 25: The cell exposure study has some basic information missing - PM dose, route of exposure (directly on filters or on PM extracts), number of times analysed (duplicate or triplicate). Please include for clarity.

Text Added:
“Each Teflon filter (PM sample or blank) was divided into two sections, one for the macrophage assay and one for chemical analysis. The filter halves used for the cell assay underwent sonication in 900 μL of purified water for approximately 16 hours at room temperature to extract the water-soluble components. These filters were then removed from the aqueous extracts, and 10x concentrated salts-glucose medium (SGM) was added to create buffered PM extract solutions for use in the PM treatments.”“Each treatment or control was run in triplicate (3 wells each). Additionally, several untreated and method blank controls were included on each 96-well plate. Zymosan was included as a positive control at a concentration of 0.125 mg-zymosan/mL in a buffered SGM solution. Results are reported as the increase in fluorescence due to sample treatments relative to the fluorescence observed in the untreated control condition.”

Comment 6: Page 5: Figure 4: The biogenic organic compounds (for example: the alpha-pinene) are believed to be more hydrophilic compared to engine exhaust organics. Please include a discussion if the water solubility of samples is also driving the difference in oxidative stress.

Text Added (to Summary and Conclusions):
“While the macrophage assay is generally more sensitive to water-soluble components of PM, as compared to non-polar PM species, the large cellular oxidative stress response to SOA, especially anthropogenic SOA, cannot be attributed entirely to hydrophilicity. Biogenic organic compounds are generally more hydrophilic than organic products of anthropogenic processes such as combustion, yet greater ROS activity in response to anthropogenic PM was observed. The alveolar macrophage assay is considered an excellent model of inhalation toxicity, and increased ROS formation reliably indexes greater toxicity, whether ultimately due to increased bioavailability of harmful molecules or simply greater quantities of harmful PM species (Landreman et al., 2008). Thus, the results of this study clearly indicate that oxidized PM species, whether of biogenic or anthropogenic origin, are more toxic that primary PM, regardless of water-solubility, with the greatest toxicity resulting from anthropogenic SOA exposures.”
Authors’ responses to specific comments of Dr. Zhi Ning:

Comment 1: Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. In some experiments, where UV rays are used to excite the organic aerosols, the elicitation of superoxide radicals is also possible.

Text Added:
“While the production of superoxide radicals is possible, the major products of H₂O oxidation generated in this type of OFR are hydroxyl radicals, especially at less than 80% relative humidity (Seinfeld & Pandis, 2016; Kamens et al., 2011; Jang et al., 2002).”

Comment 2: Page 3: Right column: Lines 28-30: The statement “aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.” is not clear. Does that mean the whole sample streaming is done for a continuous 90 minutes? Was it the same for the aerosol sampling done in dark OFR?

Text Revision:
“In the SOA condition, the aerosol stream was sampled while the UV lamp inside the reactor was on. During this condition, the sample stream was diverted for the first 90 minutes to ensure that the reactor was operating under steady-state conditions while samples were collected.”

Comment 3: Page 3: Right column: Line 33: The information of the control sample needs to be included here.

Authors’ Response:
The only control samples were the filter blanks submitted to the laboratory for chemical and toxicological analyses as discussed in Section 2.3. Discussion of the control condition utilized in the macrophage assay (untreated cells) is included in the response to Comment 5.

Comment 4: Page 4: Left column: Line 23: The analysis part has some information missing such as incubation time for cell growth, and are the same generation (life cycle) used for analysis?

Text Added:
“In preparation for PM exposures, the non-adherent fraction of macrophage cells was harvested from flasks and concentrated by centrifugation (750 RPM) for 5 minutes. The culture medium was removed, and the cell suspension was diluted to a concentration of 1,000 cells/μL. 100 μL aliquots of these suspended cells were then pipetted into each well of 96-well plates (100,000 cells/well) and incubated at 37°C/5% CO₂ for 2 hours. Following the 2-hour incubation period, nearly all macrophages were adhered to each well bottom. During PM treatments, supernatant media was aspirated and replaced with 100 μL of sample extract or blank control solution in each well.”

Comment 5: Page 4: Left column: Line 25: The cell exposure study has some basic information missing - PM dose, route of exposure (directly on filters or on PM extracts), number of times analysed (duplicate or triplicate). Please include for clarity.

Text Added:
“Each Teflon filter (PM sample or blank) was divided into two sections, one for the macrophage assay and one for chemical analysis. The filter halves used for the cell assay underwent sonication in 900 μL of purified water for approximately 16 hours at room temperature to extract the water-soluble components. These filters were then removed from the aqueous extracts, and 10x concentrated salts-glucose medium (SGM) was added to create buffered PM extract solutions for use in the PM treatments.”“Each treatment or control was run in triplicate (3 wells each). Additionally, several untreated and method blank controls were included on each 96-well plate. Zymosan was included as a positive control at a concentration of 0.125 mg-zymosan/mL in a buffered SGM solution. Results are reported as the increase in fluorescence due to sample treatments relative to the fluorescence observed in the untreated control condition.”

Comment 6: Page 5: Figure 4: The biogenic organic compounds (for example: the alpha-pinene) are believed to be more hydrophilic compared to engine exhaust organics. Please include a discussion if the water solubility of samples is also driving the difference in oxidative stress.

Text Added (to Summary and Conclusions):
“While the macrophage assay is generally more sensitive to water-soluble components of PM, as compared to non-polar PM species, the large cellular oxidative stress response to SOA, especially anthropogenic SOA, cannot be attributed entirely to hydrophilicity. Biogenic organic compounds are generally more hydrophilic than organic products of anthropogenic processes such as combustion, yet greater ROS activity in response to anthropogenic PM was observed. The alveolar macrophage assay is considered an excellent model of inhalation toxicity, and increased ROS formation reliably indexes greater toxicity, whether ultimately due to increased bioavailability of harmful molecules or simply greater quantities of harmful PM species (Landreman et al., 2008). Thus, the results of this study clearly indicate that oxidized PM species, whether of biogenic or anthropogenic origin, are more toxic that primary PM, regardless of water-solubility, with the greatest toxicity resulting from anthropogenic SOA exposures.”
Competing Interests: No competing interests. Close
Report a concern

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Reviewer Report 06 Nov 2018

Barend L. van Drooge, Institute for Environmental Assessment and Water Research (IDÆA-CSIC), Barcelona, Spain

Approved

https://doi.org/10.5256/f1000research.16832.r39486

The work of Lovett et al. presents interesting data on the possible inflammatory effects of SOA from traffic as well as biogenic (pinene) origin. The method setup is well designed, although the variables, such as conditions of relative humidity and temperature, could have been studied in different values. On the other hand, the results show that the biogenic SOA have similar high inflammatory effect in the test compared to traffic SOA, which is an important fact, and indicates that effects have been observed in real-world data. However, the study could have been more complete and higher quality if the researchers would have made an effort to detect and quantify the molecular chemical compounds that are present in the SOA fractions.

The work is suitable for indexing.

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests: No competing interests were disclosed.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

CITE

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Version 2

VERSION 2 PUBLISHED 09 Jul 2018

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Reviewer Reports

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Version 2 (revision) 11 Mar 19
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Barend L. van Drooge, Institute for Environmental Assessment and Water Research (IDÆA-CSIC), Barcelona, Spain
Zhi Ning, Hong Kong University of Science & Technology, Hong Kong, China

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Reviewer Report

21 Views

25 Feb 2019 | for Version 1

Zhi Ning, Division of Environment and Sustainability, Hong Kong University of Science & Technology, Hong Kong, China

21 Views Cite this report Responses(1)

Approved

Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. In some experiments, where UV rays are used to excite the organic aerosols, the elicitation of superoxide radicals is also possible.
Page 3: Right column: Lines 28-30: The statement “aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.” is not clear. Does that mean the whole sample streaming is done for a continuous 90 minutes? Was it the same for the aerosol sampling done in dark OFR?
Page 3: Right column: Line 33: The information of the control sample needs to be included here.
Page 4: Left column: Line 23: The analysis part has some information missing such as incubation time for cell growth, and are the same generation (life cycle) used for analysis?
Page 4: Left column: Line 25: The cell exposure study has some basic information missing - PM dose, route of exposure (directly on filters or on PM extracts), number of times analysed (duplicate or triplicate). Please include for clarity.
Page 5: Figure 4: The biogenic organic compounds (for example: the alpha-pinene) are believed to be more hydrophilic compared to engine exhaust organics. Please include a discussion if the water solubility of samples is also driving the difference in oxidative stress.

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Partly
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests

No competing interests were disclosed.

Reviewer Expertise

Particle induced cellular oxidative stress, sensor development and application

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

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Responses (1)

Author Response

05 Mar 2019

Christopher Lovett, Department of Civil and Environmental Engineering, University of Southern California, Los Angeles, 90089, USA

Authors’ responses to specific comments of Dr. Zhi Ning:

Comment 1: Page 3: Right column: Line 4: The authors can address why they have selected only Hydroxyl radicals in the investigations. In some experiments, where UV rays are used to excite the organic aerosols, the elicitation of superoxide radicals is also possible.

Text Added:
“While the production of superoxide radicals is possible, the major products of H₂O oxidation generated in this type of OFR are hydroxyl radicals, especially at less than 80% relative humidity (Seinfeld & Pandis, 2016; Kamens et al., 2011; Jang et al., 2002).”

Comment 2: Page 3: Right column: Lines 28-30: The statement “aerosol stream was sampled while a UV lamp was on, following a 90-minute reaction period.” is not clear. Does that mean the whole sample streaming is done for a continuous 90 minutes? Was it the same for the aerosol sampling done in dark OFR?

Text Revision:
“In the SOA condition, the aerosol stream was sampled while the UV lamp inside the reactor was on. During this condition, the sample stream was diverted for the first 90 minutes to ensure that the reactor was operating under steady-state conditions while samples were collected.”

Comment 3: Page 3: Right column: Line 33: The information of the control sample needs to be included here.

Authors’ Response:
The only control samples were the filter blanks submitted to the laboratory for chemical and toxicological analyses as discussed in Section 2.3. Discussion of the control condition utilized in the macrophage assay (untreated cells) is included in the response to Comment 5.

Comment 4: Page 4: Left column: Line 23: The analysis part has some information missing such as incubation time for cell growth, and are the same generation (life cycle) used for analysis?

Text Added:
“In preparation for PM exposures, the non-adherent fraction of macrophage cells was harvested from flasks and concentrated by centrifugation (750 RPM) for 5 minutes. The culture medium was removed, and the cell suspension was diluted to a concentration of 1,000 cells/μL. 100 μL aliquots of these suspended cells were then pipetted into each well of 96-well plates (100,000 cells/well) and incubated at 37°C/5% CO₂ for 2 hours. Following the 2-hour incubation period, nearly all macrophages were adhered to each well bottom. During PM treatments, supernatant media was aspirated and replaced with 100 μL of sample extract or blank control solution in each well.”

Comment 5: Page 4: Left column: Line 25: The cell exposure study has some basic information missing - PM dose, route of exposure (directly on filters or on PM extracts), number of times analysed (duplicate or triplicate). Please include for clarity.

Text Added:
“Each Teflon filter (PM sample or blank) was divided into two sections, one for the macrophage assay and one for chemical analysis. The filter halves used for the cell assay underwent sonication in 900 μL of purified water for approximately 16 hours at room temperature to extract the water-soluble components. These filters were then removed from the aqueous extracts, and 10x concentrated salts-glucose medium (SGM) was added to create buffered PM extract solutions for use in the PM treatments.”“Each treatment or control was run in triplicate (3 wells each). Additionally, several untreated and method blank controls were included on each 96-well plate. Zymosan was included as a positive control at a concentration of 0.125 mg-zymosan/mL in a buffered SGM solution. Results are reported as the increase in fluorescence due to sample treatments relative to the fluorescence observed in the untreated control condition.”

Comment 6: Page 5: Figure 4: The biogenic organic compounds (for example: the alpha-pinene) are believed to be more hydrophilic compared to engine exhaust organics. Please include a discussion if the water solubility of samples is also driving the difference in oxidative stress.

Text Added (to Summary and Conclusions):
“While the macrophage assay is generally more sensitive to water-soluble components of PM, as compared to non-polar PM species, the large cellular oxidative stress response to SOA, especially anthropogenic SOA, cannot be attributed entirely to hydrophilicity. Biogenic organic compounds are generally more hydrophilic than organic products of anthropogenic processes such as combustion, yet greater ROS activity in response to anthropogenic PM was observed. The alveolar macrophage assay is considered an excellent model of inhalation toxicity, and increased ROS formation reliably indexes greater toxicity, whether ultimately due to increased bioavailability of harmful molecules or simply greater quantities of harmful PM species (Landreman et al., 2008). Thus, the results of this study clearly indicate that oxidized PM species, whether of biogenic or anthropogenic origin, are more toxic that primary PM, regardless of water-solubility, with the greatest toxicity resulting from anthropogenic SOA exposures.”

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Reviewer Report

12 Views

06 Nov 2018 | for Version 1

Barend L. van Drooge, Institute for Environmental Assessment and Water Research (IDÆA-CSIC), Barcelona, Spain

12 Views Cite this report Responses(0)

Approved

Is the work clearly and accurately presented and does it cite the current literature?

Yes
Is the study design appropriate and is the work technically sound?

Yes
Are sufficient details of methods and analysis provided to allow replication by others?

Yes
If applicable, is the statistical analysis and its interpretation appropriate?

Yes
Are all the source data underlying the results available to ensure full reproducibility?

Yes
Are the conclusions drawn adequately supported by the results?

Yes

Competing Interests

No competing interests were disclosed.

I confirm that I have read this submission and believe that I have an appropriate level of expertise to confirm that it is of an acceptable scientific standard.

Respond to this report

Responses (0)

Alongside their report, reviewers assign a status to the article:

Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested

Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.

Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions

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Comparison of the oxidative potential of primary (POA) and secondary (SOA) organic aerosols derived from α-pinene and gasoline engine exhaust precursors

Abstract

Keywords

Introduction

Methods

Sampling methods

Figure 1. Biogenic (α-pinene) particulate matter (PM) sampling setup.

Figure 2. Anthropogenic (gasoline engine exhaust) particulate matter (PM) sampling setup.

Filter conditioning

Laboratory analyses

Results

Figure 3. Mass fractions of elemental carbon (EC) and organic carbon (OC) in engine primary organic aerosol (POA) and engine & α-pinene secondary organic aerosols (SOA).

Figure 4. Mass-fraction based oxidative potential: Engine primary organic aerosol (POA) and engine & α-pinene secondary organic aerosols (SOA).

Summary and conclusions

Data availability

Competing interests

Grant information

References

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