scholarly journals Enhanced SOA formation from mixed anthropogenic and biogenic emissions during the CARES campaign

2012 ◽  
Vol 12 (10) ◽  
pp. 26297-26349 ◽  
Author(s):  
J. E. Shilling ◽  
R. A. Zaveri ◽  
J. D. Fast ◽  
L. Kleinman ◽  
M. L. Alexander ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Biogenic Emissions ◽  
Anthropogenic Emissions ◽  
Radiation Balance ◽  
Particle Phase ◽  
Aerosol Formation ◽  
Aerosol Mass ◽  
Research Aircraft

Abstract. The CARES campaign was conducted during June 2010 in the vicinity of Sacramento, California to study aerosol formation and aging in a region where anthropogenic and biogenic emissions regularly mix. Here, we describe measurements from an Aerodyne High Resolution Aerosol Mass Spectrometer (AMS), an Ionicon Proton Transfer Reaction Mass Spectrometer (PTR-MS), and trace gas detectors (CO, NO, NOx) deployed on the G-1 research aircraft to investigate ambient gas- and particle-phase chemical composition. AMS measurements showed that the particle phase is dominated by organic aerosol (OA) (85% on average) with smaller concentrations of sulfate (5%), nitrate (6%) and ammonium (3%) observed. PTR-MS data showed that isoprene dominated the biogenic volatile organic compound concentrations (BVOCs), with monoterpene concentrations generally below the detection limit. Using two different metrics, median OA concentrations and the slope of plots of OA vs. CO concentrations (i.e. ΔOA/ΔCO), we contrast organic aerosol evolution on flight days with different prevailing meteorological conditions to elucidate the role of anthropogenic and biogenic emissions on OA formation. Airmasses influenced predominantly by biogenic emissions had median OA concentrations of 2.2 μg m−3 and near zero ΔOA/ΔCO. Those influenced predominantly by anthropogenic emissions had median OA concentrations of 4.7 μg m−3 and ΔOA/ΔCO ratios of 35–44 μg m−3 ppmv−1. But, when biogenic and anthropogenic emissions mixed, OA levels were dramatically enhanced, with median OA concentrations of 11.4 μg m−3 and ΔOA/ΔCO ratios of 77–157 μg m−3 ppmv−1. Taken together, our observations show that production of OA was enhanced when anthropogenic emissions from Sacramento mixed with isoprene-rich air from the foothills. A strong, non-linear dependence of SOA yield from isoprene is the explanation for this enhancement most consistent with both the gas- and particle-phase data. If these observations are found to be robust in other seasons and in areas outside of Sacramento, regional and global aerosol modules will need to incorporate more complex representations of NOx-dependent SOA yields into their algorithms. Ultimately, accurately predicting OA mass concentrations and their effect on radiation balance will require a mechanistically-based treatment of the interactions of biogenic and anthropogenic emissions.

scholarly journals Enhanced SOA formation from mixed anthropogenic and biogenic emissions during the CARES campaign

2013 ◽  
Vol 13 (4) ◽  
pp. 2091-2113 ◽  
Author(s):  
J. E. Shilling ◽  
R. A. Zaveri ◽  
J. D. Fast ◽  
L. Kleinman ◽  
M. L. Alexander ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Chemical Mechanism ◽  
Biogenic Emissions ◽  
Anthropogenic Emissions ◽  
Radiation Balance ◽  
Particle Phase ◽  
Aerosol Formation ◽  
Research Aircraft

Abstract. The CARES campaign was conducted during June, 2010 in the vicinity of Sacramento, California to study aerosol formation and aging in a region where anthropogenic and biogenic emissions regularly mix. Here, we describe measurements from an Aerodyne High Resolution Aerosol Mass Spectrometer (AMS), an Ionicon Proton Transfer Reaction Mass Spectrometer (PTR-MS), and trace gas detectors (CO, NO, NOx) deployed on the G-1 research aircraft to investigate ambient gas- and particle-phase chemical composition. AMS measurements showed that the particle phase is dominated by organic aerosol (OA) (85% on average) with smaller concentrations of sulfate (5%), nitrate (6%) and ammonium (3%) observed. PTR-MS data showed that isoprene dominated the biogenic volatile organic compound concentrations (BVOCs), with monoterpene concentrations generally below the detection limit. Using two different metrics, median OA concentrations and the slope of plots of OA vs. CO concentrations (i.e., ΔOA/ΔCO), we contrast organic aerosol evolution on flight days with different prevailing meteorological conditions to elucidate the role of anthropogenic and biogenic emissions on OA formation. Airmasses influenced predominantly by biogenic emissions had median OA concentrations of 2.2 μg m−3 and near zero ΔOA/ΔCO. Those influenced predominantly by anthropogenic emissions had median OA concentrations of 4.7 μg m−3 and ΔOA/ΔCO ratios of 35–44 μg m−3 ppmv. But, when biogenic and anthropogenic emissions mixed, OA levels were enhanced, with median OA concentrations of 11.4 μg m−3 and ΔOA/ΔCO ratios of 77–157 μg m−3 ppmv. Taken together, our observations show that production of OA was enhanced when anthropogenic emissions from Sacramento mixed with isoprene-rich air from the foothills. After considering several anthropogenic/biogenic interaction mechanisms, we conclude that NOx concentrations play a strong role in enhancing SOA formation from isoprene, though the chemical mechanism for the enhancement remains unclear. If these observations are found to be robust in other seasons and in areas outside of Sacramento, regional and global aerosol modules will need to incorporate more complex representations of NOx-dependent SOA mechanisms and yields into their algorithms. Ultimately, accurately predicting OA mass concentrations and their effect on radiation balance will require a mechanistically-based treatment of the interactions of biogenic and anthropogenic emissions.

scholarly journals Secondary organic aerosol formation and primary organic aerosol oxidation from biomass-burning smoke in a flow reactor during FLAME-3

2013 ◽  
Vol 13 (22) ◽  
pp. 11551-11571 ◽  
Author(s):  
A. M. Ortega ◽  
D. A. Day ◽  
M. J. Cubison ◽  
W. H. Brune ◽  
D. Bon ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Biomass Burning ◽  
Flow Reactor ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Oxidation Products ◽  
Chemical Transformations ◽  
Aerosol Formation ◽  
Aerosol Mass ◽  
Smog Chambers

Abstract. We report the physical and chemical effects of photochemically aging dilute biomass-burning smoke. A "potential aerosol mass" (PAM) flow reactor was used with analysis by a high-resolution aerosol mass spectrometer and a proton-transfer-reaction ion-trap mass spectrometer during the FLAME-3 campaign. Hydroxyl (OH) radical concentrations in the reactor reached up to ~1000 times average tropospheric levels, producing effective OH exposures equivalent to up to 5 days of aging in the atmosphere, and allowing for us to extend the investigation of smoke aging beyond the oxidation levels achieved in traditional smog chambers. Volatile organic compound (VOC) observations show aromatics and terpenes decrease with aging, while formic acid and other unidentified oxidation products increase. Unidentified gas-phase oxidation products, previously observed in atmospheric and laboratory measurements, were observed here, including evidence of multiple generations of photochemistry. Substantial new organic aerosol (OA) mass ("net SOA"; secondary OA) was observed from aging biomass-burning smoke, resulting in total OA average of 1.42 ± 0.36 times the initial primary OA (POA) after oxidation. This study confirms that the net-SOA-to-POA ratio of biomass-burning smoke is far lower on average than that observed for urban emissions. Although most fuels were very reproducible, significant differences were observed among the biomasses, with some fuels resulting in a doubling of the OA mass, while for others a very small increase or even a decrease was observed. Net SOA formation in the photochemical reactor increased with OH exposure (OHexp), typically peaking around three days of equivalent atmospheric photochemical age (OHexp~3.9 × 1011 molecules cm−3 s), then leveling off at higher exposures. The amount of additional OA mass added from aging is positively correlated with initial POA concentration, but not with the total VOC concentration or the concentration of known SOA precursors. The mass of SOA formed often exceeded the mass of the known VOC precursors, indicating the likely importance of primary semivolatile/intermediate volatility species, and possibly of unidentified VOCs as SOA precursors in biomass burning smoke. Chemical transformations continued even after mass concentration stabilized. Changes in the biomass-burning tracer f60 ranged from substantially decreasing to remaining constant with increased aging. With increased OHexp, oxidation was always detected (as indicated by f44 and O/C). POA O/C ranged from 0.15 to 0.5, while aged OA O/C reached up to 0.87. The rate of oxidation and maximum O/C achieved differs for each biomass, and appears to increase with the initial O/C of the POA.

scholarly journals Airborne Extractive Electrospray Mass Spectrometry Measurements of the Chemical Composition of Organic Aerosol

2020 ◽  
Author(s):  
Demetrios Pagonis ◽  
Pedro Campuzano-Jost ◽  
Hongyu Guo ◽  
Douglas A. Day ◽  
Melinda K. Schueneman ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Precise Control ◽  
Airborne Measurements ◽  
Regression Slope ◽  
Aerosol Mass ◽  
Research Aircraft ◽  
Working Solution ◽  
Field Intercomparison

Abstract. We deployed an extractive electrospray ionization time-of-flight mass spectrometer (EESI-MS) for airborne measurements of biomass burning aerosol during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) study onboard the NASA DC-8 research aircraft. Through optimization of the electrospray working solution, active control of the electrospray region pressure, and precise control of electrospray capillary position, we achieved 1 Hz quantitative measurements of aerosol nitrocatechol and levoglucosan concentrations up to pressure altitudes of 7 km. EESI-MS response to levoglucosan and nitrocatechol was calibrated for each flight, with flight-to-flight calibration variability of 60 % (1σ). Laboratory measurements showed no aerosol size dependence in EESI-MS sensitivity below particle geometric diameters of 400 nm, covering 82 % of accumulation mode aerosol mass during FIREX-AQ. We also present a first in-field intercomparison of EESI-MS with a chemical analysis of aerosol online proton-transfer-reaction mass spectrometer (CHARON PTR-MS) and a high-resolution Aerodyne aerosol mass spectrometer (AMS). EESI-MS and CHARON PTR-MS levoglucosan concentrations were well correlated, with a regression slope of 0.94, R2 = 0.77. AMS levoglucosan-equivalent concentrations and EESI-MS levoglucosan showed greater difference, with a regression slope of 1.36, R2 = 0.96, likely indicating the contribution of other compounds to the AMS levoglucosan-equivalent measurement. Total EESI-MS signal showed correlation (R2 = 0.9) with total organic aerosol measured by AMS, and the EESI-MS bulk organic aerosol sensitivity was 60 % of the sensitivity to levoglucosan standards.

scholarly journals Airborne extractive electrospray mass spectrometry measurements of the chemical composition of organic aerosol

2021 ◽  
Vol 14 (2) ◽  
pp. 1545-1559
Author(s):  
Demetrios Pagonis ◽  
Pedro Campuzano-Jost ◽  
Hongyu Guo ◽  
Douglas A. Day ◽  
Melinda K. Schueneman ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Precise Control ◽  
Airborne Measurements ◽  
Regression Slope ◽  
Aerosol Mass ◽  
Research Aircraft ◽  
Working Solution ◽  
Field Intercomparison

Abstract. We deployed an extractive electrospray ionization time-of-flight mass spectrometer (EESI-MS) for airborne measurements of biomass burning aerosol during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) study onboard the NASA DC-8 research aircraft. Through optimization of the electrospray working solution, active control of the electrospray region pressure, and precise control of electrospray capillary position, we achieved 1 Hz quantitative measurements of aerosol nitrocatechol and levoglucosan concentrations up to pressure altitudes of 7 km. The EESI-MS response to levoglucosan and nitrocatechol was calibrated for each flight, with flight-to-flight calibration variability of 60 % (1σ). Laboratory measurements showed no aerosol size dependence in EESI-MS sensitivity below particle geometric diameters of 400 nm, covering 82 % of accumulation-mode aerosol mass during FIREX-AQ. We also present a first in-field intercomparison of EESI-MS with a chemical analysis of aerosol online proton-transfer-reaction mass spectrometer (CHARON PTR-MS) and a high-resolution Aerodyne aerosol mass spectrometer (AMS). EESI-MS and CHARON PTR-MS levoglucosan concentrations were well correlated, with a regression slope of 0.94 (R2=0.77). AMS levoglucosan-equivalent concentrations and EESI-MS levoglucosan showed a greater difference, with a regression slope of 1.36 (R2=0.96), likely indicating the contribution of other compounds to the AMS levoglucosan-equivalent measurement. The total EESI-MS signal showed correlation (R2=0.9) with total organic aerosol measured by AMS, and the EESI-MS bulk organic aerosol sensitivity was 60 % of the sensitivity to levoglucosan standards.

scholarly journals Primary and secondary organic aerosol origin by combined gas-particle phase source apportionment

2013 ◽  
Vol 13 (3) ◽  
pp. 8537-8583 ◽  
Author(s):  
M. Crippa ◽  
F. Canonaco ◽  
J. G. Slowik ◽  
I. El Haddad ◽  
P. F. DeCarlo ◽  
...  
Keyword(s):  
Source Apportionment ◽  
Mass Spectrometer ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Anthropogenic Sources ◽  
Particle Phase ◽  
Aerosol Mass Spectrometer ◽  
Aerosol Mass ◽  
Formation And Evolution

Abstract. Secondary organic aerosol (SOA), a predominant fraction of particulate organic mass (OA), remains poorly constrained. Its formation involves several unknown precursors, formation and evolution pathways and multiple natural and anthropogenic sources. Here a combined gas-particle phase source apportionment is applied to wintertime and summertime data collected in the megacity of Paris in order to investigate SOA origin during both seasons. This was possible by combining the information provided by an aerosol mass spectrometer (AMS) and a proton transfer reaction mass spectrometer (PTR-MS). A better constrained apportionment of primary OA (POA) sources is also achieved using this methodology, making use of gas-phase tracers. These tracers allowed distinguishing between biogenic and continental/anthropogenic sources of SOA. We found that continental SOA was dominant during both seasons (24–50% of total OA), while contributions from photochemistry-driven SOA (9% of total OA) and marine emissions (13% of total OA) were also observed during summertime. A semi-volatile nighttime component was also identified (up to 18% of total OA during wintertime). This approach was successfully applied here and implemented in a new source apportionment toolkit.

scholarly journals Secondary organic aerosol formation and primary organic aerosol oxidation from biomass burning smoke in a flow reactor during FLAME-3

2013 ◽  
Vol 13 (5) ◽  
pp. 13799-13851 ◽  
Author(s):  
A. M. Ortega ◽  
D. A. Day ◽  
M. J. Cubison ◽  
W. H. Brune ◽  
D. Bon ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Biomass Burning ◽  
Ion Trap ◽  
Flow Reactor ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Oxidation Products ◽  
Chemical Transformations ◽  
Aerosol Formation ◽  
Aerosol Mass

Abstract. We report the physical and chemical effects of photochemically aging dilute biomass-burning smoke. A potential aerosol mass "PAM" flow reactor was used with analysis by a high-resolution aerosol mass spectrometer and a proton-transfer reaction ion-trap mass spectrometer during the FLAME-3 campaign. Hydroxyl (OH) radical concentrations in the reactor reached up to ~ 1000 times average tropospheric levels, producing effective OH exposures equivalent to up to 5 days aging in the atmosphere. VOC observations show aromatics and terpenes decrease with aging, while formic acid and other unidentified oxidation products increase. Unidentified gas-phase oxidation products, previously observed in atmospheric and laboratory measurements, were observed here, including evidence of multiple generations of photochemistry. Substantial new organic aerosol (OA) mass ("net SOA"; secondary OA) was observed from aging biomass-burning smoke, resulting in an total OA average of 1.42 ± 0.36 times the initial primary OA (POA) after oxidation. This study confirms that the net SOA to POA ratio of biomass burning smoke is far lower on average than that observed for urban emissions. Although most fuels were very reproducible, significant differences were observed among the biomasses, with some fuels resulting in a doubling of the OA mass, while for others a very small increase or even a decrease was observed. Net SOA formation in the photochemical reactor increased with OH exposure (OHexp), typically peaking around three days of equivalent atmospheric photochemical age (OHexp ~ 3.9 × 1011 molecules cm−3 s−1), then leveling off at higher exposures. The amount of additional OA mass added from aging is positively correlated with initial POA concentration, but not with the total VOC concentration or the concentration of known SOA precursors. The mass of SOA formed often exceeds the mass of the known VOC precursors, indicating the likely importance of primary semivolatile/intermediate volatility species, and possibly of unidentified VOCs as SOA precursors in biomass burning smoke. Chemical transformations continue even after mass concentration stabilizes. Changes in the biomass-burning tracer f60 ranged from substantially decreasing to remaining constant with increased aging. With increased OHexp, oxidation was always detected (as indicated by f44 and O/C). POA O/C ranged 0.15–0.5, while aged OA O/C reached up to 0.87. The rate of oxidation and maximum O/C achieved differs for each biomass and appears to increase with the initial O/C of the POA.

scholarly journals Primary and secondary organic aerosol origin by combined gas-particle phase source apportionment

2013 ◽  
Vol 13 (16) ◽  
pp. 8411-8426 ◽  
Author(s):  
M. Crippa ◽  
F. Canonaco ◽  
J. G. Slowik ◽  
I. El Haddad ◽  
P. F. DeCarlo ◽  
...  
Keyword(s):  
Source Apportionment ◽  
Mass Spectrometer ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Anthropogenic Sources ◽  
Particle Phase ◽  
Aerosol Mass Spectrometer ◽  
Aerosol Mass ◽  
Formation And Evolution

Abstract. Secondary organic aerosol (SOA), a prominent fraction of particulate organic mass (OA), remains poorly constrained. Its formation involves several unknown precursors, formation and evolution pathways and multiple natural and anthropogenic sources. Here a combined gas-particle phase source apportionment is applied to wintertime and summertime data collected in the megacity of Paris in order to investigate SOA origin during both seasons. This was possible by combining the information provided by an aerosol mass spectrometer (AMS) and a proton transfer reaction mass spectrometer (PTR-MS). A better constrained apportionment of primary OA (POA) sources is also achieved using this methodology, making use of gas-phase tracers. These tracers made possible the discrimination between biogenic and continental/anthropogenic sources of SOA. We found that continental SOA was dominant during both seasons (24–50% of total OA), while contributions from photochemistry-driven SOA (9% of total OA) and marine emissions (13% of total OA) were also observed during summertime. A semi-volatile nighttime component was also identified (up to 18% of total OA during wintertime). This approach was successfully applied here and implemented in a new source apportionment toolkit.

scholarly journals Secondary organic aerosol formation from reaction of tertiary amines with nitrate radical

2008 ◽  
Vol 8 (4) ◽  
pp. 16585-16608 ◽  
Author(s):  
M. E. Erupe ◽  
D. J. Price ◽  
P. J. Silva ◽  
Q. G. J. Malloy ◽  
L. Qi ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Nitrate Radical ◽  
Tertiary Amines ◽  
Aerosol Formation ◽  
Night Time ◽  
Aerosol Mass Spectrometer ◽  
Aerosol Mass ◽  
Secondary Organic Aerosol Formation

Abstract. Secondary organic aerosol formation from the reaction of tertiary amines with nitrate radical was investigated in an indoor environmental chamber. Particle chemistry was monitored using a high resolution aerosol mass spectrometer while gas-phase species were detected using a proton transfer reaction mass spectrometer. Trimethylamine, triethylamine and tributylamine were studied. Results indicate that tributylamine forms the most aerosol mass followed by trimethylamine and triethylamine respectively. Spectra from the aerosol mass spectrometer indicate the formation of complex non-salt aerosol products. We propose a reaction mechanism that proceeds via abstraction of a proton by nitrate radical followed by RO2 chemistry. Rearrangement of the aminyl alkoxy radical through hydrogen shift leads to the formation of hydroxylated amides, which explain most of the higher mass ions in the mass spectra. These experiments show that oxidation of tertiary amines by nitrate radical may be an important night-time source of secondary organic aerosol.

scholarly journals Characterization of fresh and aged organic aerosol emissions from meat charbroiling

2017 ◽  
Vol 17 (11) ◽  
pp. 7143-7155 ◽  
Author(s):  
Christos Kaltsonoudis ◽  
Evangelia Kostenidou ◽  
Evangelos Louvaris ◽  
Magda Psichoudaki ◽  
Epameinondas Tsiligiannis ◽  
...  
Keyword(s):  
Mass Spectrometer ◽  
Urban Areas ◽  
Fine Particulate Matter ◽  
Organic Aerosol ◽  
Proton Transfer Reaction ◽  
Gas Phases ◽  
Uv Illumination ◽  
Aerosol Mass ◽  
Inorganic Species ◽  
Aerosol Emissions

Abstract. Cooking emissions can be a significant source of fine particulate matter in urban areas. In this study the aerosol- and gas-phase emissions from meat charbroiling were characterized. Greek souvlakia with pork were cooked using a commercial charbroiler and a fraction of the emissions were introduced into a smog chamber where after a characterization phase they were exposed to UV illumination and oxidants. The particulate and gas phases were characterized by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a proton-transfer-reaction mass spectrometer (PTR-MS) correspondingly. More than 99 % of the aerosol emitted was composed of organic compounds, while black carbon (BC) contributed 0.3 % and the inorganic species less than 0.5 % of the total aerosol mass. The initial O  :  C ratio was approximately 0.09 and increased up to 0.30 after a few hours of chemical aging (exposures of 1010 molecules cm−3 s for OH and 100 ppb h for ozone). The initial and aged AMS spectra differed considerably (θ =  27°). Ambient measurements were also conducted during Fat Thursday in Patras, Greece, when traditionally meat is charbroiled everywhere in the city. Positive matrix factorization (PMF) revealed that cooking organic aerosol (COA) reached up to 85 % of the total OA from 10:00 to 12:00 LST that day. The ambient COA factor in two major Greek cities had a mass spectrum during spring and summer similar to the aged meat charbroiling emissions. In contrast, the ambient COA factor during winter resembled strongly the fresh laboratory meat charbroiling emissions.

scholarly journals Examining the effects of anthropogenic emissions on isoprene-derived secondary organic aerosol formation during the 2013 Southern Oxidant and Aerosol Study (SOAS) at the Look Rock, Tennessee ground site

2015 ◽  
Vol 15 (15) ◽  
pp. 8871-8888 ◽  
Author(s):  
S. H. Budisulistiorini ◽  
X. Li ◽  
S. T. Bairai ◽  
J. Renfro ◽  
Y. Liu ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Anthropogenic Emissions ◽  
Strongly Correlated ◽  
Particle Phase ◽  
Aerosol Formation ◽  
Aerosol Acidity ◽  
Southeastern Us

Abstract. A suite of offline and real-time gas- and particle-phase measurements was deployed at Look Rock, Tennessee (TN), during the 2013 Southern Oxidant and Aerosol Study (SOAS) to examine the effects of anthropogenic emissions on isoprene-derived secondary organic aerosol (SOA) formation. High- and low-time-resolution PM2.5 samples were collected for analysis of known tracer compounds in isoprene-derived SOA by gas chromatography/electron ionization-mass spectrometry (GC/EI-MS) and ultra performance liquid chromatography/diode array detection-electrospray ionization-high-resolution quadrupole time-of-flight mass spectrometry (UPLC/DAD-ESI-HR-QTOFMS). Source apportionment of the organic aerosol (OA) was determined by positive matrix factorization (PMF) analysis of mass spectrometric data acquired on an Aerodyne Aerosol Chemical Speciation Monitor (ACSM). Campaign average mass concentrations of the sum of quantified isoprene-derived SOA tracers contributed to ~ 9 % (up to 28 %) of the total OA mass, with isoprene-epoxydiol (IEPOX) chemistry accounting for ~ 97 % of the quantified tracers. PMF analysis resolved a factor with a profile similar to the IEPOX-OA factor resolved in an Atlanta study and was therefore designated IEPOX-OA. This factor was strongly correlated (r2 > 0.7) with 2-methyltetrols, C5-alkene triols, IEPOX-derived organosulfates, and dimers of organosulfates, confirming the role of IEPOX chemistry as the source. On average, IEPOX-derived SOA tracer mass was ~ 26 % (up to 49 %) of the IEPOX-OA factor mass, which accounted for 32 % of the total OA. A low-volatility oxygenated organic aerosol (LV-OOA) and an oxidized factor with a profile similar to 91Fac observed in areas where emissions are biogenic-dominated were also resolved by PMF analysis, whereas no primary organic aerosol (POA) sources could be resolved. These findings were consistent with low levels of primary pollutants, such as nitric oxide (NO ~ 0.03 ppb), carbon monoxide (CO ~ 116 ppb), and black carbon (BC ~ 0.2 μg m−3). Particle-phase sulfate is fairly correlated (r2 ~ 0.3) with both methacrylic acid epoxide (MAE)/hydroxymethyl-methyl-α-lactone (HMML)- (henceforth called methacrolein (MACR)-derived SOA tracers) and IEPOX-derived SOA tracers, and more strongly correlated (r2 ~ 0.6) with the IEPOX-OA factor, in sum suggesting an important role of sulfate in isoprene SOA formation. Moderate correlation between the MACR-derived SOA tracer 2-methylglyceric acid with sum of reactive and reservoir nitrogen oxides (NOy; r2 = 0.38) and nitrate (r2 = 0.45) indicates the potential influence of anthropogenic emissions through long-range transport. Despite the lack of a clear association of IEPOX-OA with locally estimated aerosol acidity and liquid water content (LWC), box model calculations of IEPOX uptake using the simpleGAMMA model, accounting for the role of acidity and aerosol water, predicted the abundance of the IEPOX-derived SOA tracers 2-methyltetrols and the corresponding sulfates with good accuracy (r2 ~ 0.5 and ~ 0.7, respectively). The modeling and data combined suggest an anthropogenic influence on isoprene-derived SOA formation through acid-catalyzed heterogeneous chemistry of IEPOX in the southeastern US. However, it appears that this process was not limited by aerosol acidity or LWC at Look Rock during SOAS. Future studies should further explore the extent to which acidity and LWC as well as aerosol viscosity and morphology becomes a limiting factor of IEPOX-derived SOA, and their modulation by anthropogenic emissions.

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