ALBERT

Description: Laboratory smog chamber experiments have been carried out to investigate secondary organic aerosol (SOA) formation from the photooxidation of naphthalene and its methyl analogs, 1- and 2-methylnaphthalene (1-MN and 2-MN, respectively). Laboratory smog chamber irradiations were conducted in a flow mode to ensure adequate collection of the aerosol at reasonably low reactant concentrations and in the presence and absence of nitrogen oxides. Phthalic acid and methyl analogs were identified following BSTFA derivatization of the aerosol extract. These compounds were examined to determine whether they could serve as reasonable molecular tracers to estimate the contributions of these precursors to ambient PM2.5. Measurements were also made to determine aerosol parameters from secondary organic aerosol from naphthalene, 1-MN, and 2-MN. A mass fraction approach was used to establish factors which could be applied to phthalic acid concentrations in ambient aerosols, assuming a negligible contribution from primary sources. Phthalic anhydride uptake (and hydrolysis) was tested and found to represent a moderate filter artifact in filter measurements with and without in-line denuders. This study provided the opportunity to examine differences using authentic standards for phthalic acid compared to surrogate standards. While the mass fraction based on a surrogate compounds was somewhat lower, the differences are largely unimportant. For naphthalene, mass fractions of 0.0199 (recommended for ambient samples) and 0.0206 were determined in the presence and absence of nitrogen oxides, respectively, based on phthalic acid standards. The mass fractions determined from the laboratory data were applied to ambient samples where phthalic acid was found and expressed "as naphthalene" since phthalic acid was found to be produced in the particle phase from other methylnaphthalenes. The mass fraction values were applied to samples taken during the 2005 SOAR Study in Riverside, CA and 2010 CalNex Study in Pasadena. In both studies an undetermined isomer of methylphthalic acid was detected in addition to phthalic acid. Laboratory experiment retention times and mass spectra suggest that the major precursor for this compound is 2-MN. For the CalNex Study, SOC values for the 2-ring precursor PAHs (as naphthalene) were found to range from below the detection limit to 20 ngC m−3 which with the laboratory mass fraction data suggests an upper limit of approximately 1 μg m−3 for SOA due to 2-ring PAHs. Temporal data over the course of the one-month CalNex study suggest that primary sources of phthalic acid were probably negligible during this study period. However, the values must still be considered upper limits given a potential hydrolysis reaction or uptake of phthalic anhydride (subsequently hydrolyzed) onto the collection media.

Description: The formation of secondary organic aerosol (SOA) generated by irradiating 2-methyl-3-buten-2-ol (MBO) in the presence and/or absence of NOx, H2O2, and/or SO2 was examined. Experiments were conducted in smog chambers operated in either dynamic or static mode. A filter/denuder sampling system was used for simultaneously collecting gas- and particle-phase products. The structural characterization of gas and particulate products was investigated using BSTFA, BSTFA + PFBHA, and DNPH derivatization techniques followed by GC-MS and liquid chromatography analysis. This analysis showed the occurrence of more than 68 oxygenated organic compounds in the gas and particle phases, 28 of which were tentatively identified. The major components observed include 2,3-dihydroxyisopentanol (DHIP), 2-hydroxy-2-oxoisopentanol, 2,3-dihydroxy-3-methylbutanal, 2,3-dihydroxy-2-methylsuccinic acid, 2-hydroxy-2-methylpropanedioic acid, acetone, glyoxal, methylglyoxal, glycolaldehyde, and formaldehyde. Most of these oxygenated compounds were detected for the first time in this study. While measurements of the gas-phase photooxidation products have been made, the focus of this work has been an examination of the particle phase. SOA from some experiments was analyzed for the organic mass to organic carbon ratio (OM/OC), the effective enthalpy of vaporization (ΔHvapeff), and the aerosol yield. Additionally, aerosol size, volume, and number concentrations were measured by a Scanning Mobility Particle Sizer coupled to a Condensation Particle Counter system. The OM/OC ratio was 2.1 in the MBO/H2O2 system. The ΔHvapeff was 41 kJ mol−1, a value similar to that of isoprene SOA. The laboratory SOA yield measured in this study was 0.7% in MBO/H2O2 for an aerosol mass of 33 μg m−3. Secondary organic aerosol was found to be negligible under conditions with oxides of nitrogen (NOx) present. Time profiles and proposed reaction schemes are provided for selected compounds. The contribution of SOA products from MBO oxidation to ambient PM2.5 was investigated by analyzing a series of ambient PM2.5 samples collected in several places around the United States. In addition to the occurrence of several organic compounds in both field and laboratory samples, DHIP was found to originate only from the oxidation of MBO, and therefore this compound could potentially serve as a tracer for MBO SOA. Initial attempts have been made to quantify the concentrations of DHIP and other compounds based on surrogate compound calibrations. The average concentrations of DHIP in ambient PM2.5 samples from Duke Forest in North Carolina ranged from zero during cold seasons to approximately 1 ng m−3 during warm seasons. This appears to be the first time that DHIP has been detected in ambient PM2.5 samples. The occurrence of several other compounds in both laboratory and field samples suggests that SOA originating from MBO can contribute under selected ambient conditions to the ambient aerosol mainly in areas where MBO emissions are high.

Description: The secondary organic aerosol (SOA) yield of β-caryophyllene photooxidation is enhanced by aerosol acidity. In the present study, the influence of aerosol acidity on the chemical composition of β-caryophyllene SOA is investigated using ultra performance liquid chromatography/electrospray ionization-time-of-flight mass spectrometry (UPLC/ESI-TOFMS). A number of first-, second- and higher-generation gas-phase products having carbonyl and carboxylic acid functional groups are detected in the particle phase. Particle-phase reaction products formed via hydration and organosulfate formation processes are also detected. Increased acidity leads to different effects on the abundance of individual products; significantly, abundances of organosulfates are correlated with aerosol acidity. To our knowledge, this is the first detection of organosulfates and nitrated organosulfates derived from a sesquiterpene. The increase of certain particle-phase reaction products with increased acidity provides chemical evidence to support the acid-enhanced SOA yields. Based on the agreement between the chromatographic retention times and accurate mass measurements of chamber and field samples, three β-caryophyllene products (i.e., β-nocaryophyllon aldehyde, β-hydroxynocaryophyllon aldehyde, and β-dihydroxynocaryophyllon aldehyde) are suggested as chemical tracers for β-caryophyllene SOA. These compounds are detected in both day and night ambient samples collected in downtown Atlanta, GA and rural Yorkville, GA during the 2008 August Mini-Intensive Gas and Aerosol Study (AMIGAS).

Description: The formation of secondary organic aerosol (SOA) generated by irradiating 2-methyl-3-buten-2-ol (MBO) in the presence and/or absence of NOx, H2O2, and/or SO2 was examined. Experiments were conducted in smog chambers operated either in dynamic or steady-state mode. A filter/denuder sampling system was used for simultaneously collecting gas and particle phase products. The structural characterization of gas and particulate products was investigated using BSTFA, BSTFA + PFBHA, and DNPH derivatization techniques followed by GC-MS and liquid chromatography analysis. This analysis showed the occurrence of more than 68 oxygenated organic compounds in the gas and particle phase, 28 of which were identified. The major components observed include 2,3-dihydroxyisopentanol (DHIP), 2-hydroxy-2-oxoisopentanol, 2,3-dihydroxy-3-methylbutanal, 2,3-dihydroxy-2-methylsuccinic acid, 2-hydroxy-2-methylpropanedioic acid, acetone, glyoxal, methylglyoxal, glycolaldehyde, and formaldehyde. Most of these oxygenated compounds were detected for the first time in this study. While measurements of the gas phase photooxidation products have been made, the focus of this work has been an examination of the particle phase. SOA from some experiments was analyzed for the organic mass to organic carbon ratio (OM/OC), the effective enthalpy of vaporization (ΔHvapeff), and the aerosol yield. Additionally, aerosol size, volume, and number concentrations were measured by a Scanning Mobility Particle Sizer coupled to a Condensation Particle Counter system. The OM/OC was found to be 2.1 in MBO/H2O2 system. The ΔHvapeff was 41 kJ mol−1, a value similar to that of isoprene SOA. The laboratory SOA yield measured in this study was found to be 0.7 % in MBO/H2O2 for an aerosol mass of 33 μg m−3. Time profiles and proposed reaction schemes are provided for selected compounds. The contribution of SOA products from MBO oxidation to ambient PM2.5 was investigated by analyzing a series of ambient PM2.5 samples collected in several places around the United States. In addition to the occurrence of several organic compounds in both field and laboratory samples, DHIP was found to originate only from the oxidation of MBO, and therefore this compound could serve as a tracer for MBO SOA. Initial attempts have been made to quantify the concentrations of DHIP and other compounds based on surrogate compound calibrations. The average concentrations of DHIP in ambient PM2.5 samples from Duke Forest, NC ranged from zero during cold seasons in areas with low MBO emission rates to approximately 1 ng m−3 during warm seasons in areas with high MBO emission rates. This appears to be the first time that DHIP has been detected in ambient PM2.5 samples. The occurrence of several other compounds in both laboratory and field samples suggests that SOA originating from MBO can contribute under selected ambient conditions to the ambient aerosol mainly in areas where MBO emissions are high.

Description: Laboratory smog chamber experiments have been carried out to investigate secondary organic aerosol (SOA) formation from the photooxidation of naphthalene and its methyl analogs, 1- and 2-methylnaphthalene (1-MN and 2-MN, respectively). Laboratory smog chamber irradiations were conducted in a flow mode to ensure adequate collection of the aerosol at reasonably low reactant concentrations and in the presence and absence of nitrogen oxides. Phthalic acid and methyl analogs were identified following BSTFA derivatization of the aerosol extract. These compounds were examined to determine whether they could serve as reasonable molecular tracers to estimate the contributions of these precursors to ambient PM2.5. Measurements were also made to determine aerosol parameters from secondary organic aerosol from naphthalene, 1-MN, and 2-MN. A mass fraction approach was used to establish factors which could be applied to phthalic acid concentrations in ambient aerosols, assuming a negligible contribution from primary sources. In addition, the hydrolysis of phthalic anhydride was tested and found to represent a moderate filter artifact in side-by-side filter measurements with and without in-line denuders. This study also provided the opportunity to examine numeric differences using authentic standards for phthalic acid compared to surrogate standards. While the mass fraction based on a surrogate compounds was somewhat lower, the differences are largely unimportant. For naphthalene, mass fractions of 0.023 and 0.019 were determined in the presence and absence of nitrogen oxides, respectively, based on the phthalic acid standards. The mass fractions determined from the laboratory data were then applied to ambient samples where phthalic acid was found and expressed "as naphthalene" since phthalic acid was found to be produced in the particle phase from other PAHs tested. The mass fraction values were applied to samples taken during the 2005 SOAR Study in Riverside, CA and 2010 CalNex Study in Pasadena. In both studies an undetermined isomer of methylphthalic acid was detected in addition to phthalic acid. Laboratory experiment retention times and mass spectra suggest that the major precursor for this compound is 2-MN. For the CalNex Study, SOC values for the gas-phase PAHs (as naphthalene) were found to range from below the detection limit to 20 ng C m−3 which together with the laboratory mass fraction data suggests an upper limit of 1 μg m−3 for SOA due to PAHs. Temporal data over the course of the one-month CalNex study suggest that primary sources of phthalic acid were probably negligible during this study period. However, the values must still be considered upper limits given a potential gas-phase hydrolysis reaction or uptake of phthalic anhydride (subsequently hydrolyzed) onto the collection medium.

Description: Secondary organic aerosol (SOA) was generated by irradiating 1,3-butadiene (13BD) in the presence of H2O2 or NOx. Experiments were conducted in a smog chamber operated in either flow or batch mode. A filter/denuder sampling system was used for simultaneously collecting gas- and particle-phase products. The chemical composition of the gas phase and SOA was analyzed using derivative-based methods (BSTFA, BSTFA + PFBHA, or DNPH) followed by gas chromatography–mass spectrometry (GC-MS) or high-performance liquid chromatography (HPLC) analysis of the derivative compounds. The analysis showed the occurrence of more than 60 oxygenated organic compounds in the gas and particle phases, of which 31 organic monomers were tentatively identified. The major identified products include glyceric acid, d-threitol, erythritol, d-threonic acid, meso-threonic acid, erythrose, malic acid, tartaric acid, and carbonyls including glycolaldehyde, glyoxal, acrolein, malonaldehyde, glyceraldehyde, and peroxyacryloyl nitrate (APAN). Some of these were detected in ambient PM2.5 samples and could potentially serve as organic markers of 1,3-butadiene (13BD). Furthermore, a series of oligoesters were detected and found to be produced from esterification reactions among compounds bearing alcoholic groups and compounds bearing acidic groups. Time profiles are provided for selected compounds. SOA was analyzed for organic mass to organic carbon (OM / OC) ratio, effective enthalpy of vaporization (ΔHvapeff), and aerosol yield. The average OM / OC ratio and SOA density were 2.7 ± 0.09 and 1.2 ± 0.05, respectively. The average ΔHvapeff was 26.1 ± 1.5 kJ mol−1, a value lower than that of isoprene SOA. The average laboratory SOA yield measured in this study at aerosol mass concentrations between 22.5 and 140.2 μg m−3 was 0.025 ± 0.011, a value consistent with the literature (0.021–0.178). While the focus of this study has been examination of the particle-phase measurements, the gas-phase photooxidation products have also been examined. The contribution of SOA products from 13BD oxidation to ambient PM2.5 was investigated by analyzing a series of ambient PM2.5 samples collected in several locations around the United States. In addition to the occurrence of several organic compounds in field and laboratory samples, glyceric acid, d-threitol, erythritol, erythrose, and threonic acid were found to originate only from the oxidation of 13BD based on our previous experiments involving chamber oxidation of a series of hydrocarbons. Initial attempts have been made to quantify the concentrations of these compounds. The average concentrations of these compounds in ambient PM2.5 samples from the California Research at the Nexus of Air Quality and Climate Change (CalNex) study ranged from 0 to approximately 14.1 ng m−3. The occurrence of several other compounds in both laboratory and field samples suggests that SOA originating from 13BD oxidation could contribute to the ambient aerosol mainly in areas with high 13BD emission rates.

Description: Four different parameterizations for the formation and evolution of secondary organic aerosol (SOA) are evaluated using a 0-D box model representing the Los Angeles Metropolitan Region during the CalNex 2010 field campaign. We constrain the model predictions with measurements from several platforms and compare predictions with particle and gas-phase observations from the CalNex Pasadena ground site. That site provides a unique opportunity to study aerosol formation close to anthropogenic emission sources with limited recirculation. The model SOA formed only from the oxidation of VOCs (V-SOA) is insufficient to explain the observed SOA concentrations, even when using SOA parameterizations with multi-generation oxidation that produce much higher yields than have been observed in chamber experiments, or when increasing yields to their upper limit estimates accounting for recently reported losses of vapors to chamber walls. The Community Multiscale Air Quality (WRF-CMAQ) model (version 5.0.1) provides excellent predictions of secondary inorganic particle species but underestimates the observed SOA mass by a factor of 25 when an older VOC-only parameterization is used, which is consistent with many previous model-measurement comparisons for pre-2007 anthropogenic SOA modules in urban areas. Including SOA from primary semi-volatile and intermediate volatility organic compounds (P-S/IVOCs) following the parameterizations of Robinson et al. (2007), Grieshop et al. (2009), or Pye and Seinfeld (2010) improves model/measurement agreement for mass concentration. When comparing the three parameterizations, the Grieshop et al. (2009) parameterization more accurately reproduces both the SOA mass concentration and oxygen-to-carbon ratio inside the urban area. Our results strongly suggest that other precursors besides VOCs, such as P-S/IVOCs, are needed to explain the observed SOA concentrations in Pasadena. All the parameterizations over-predict urban SOA formation at long photochemical ages (≈ 3 days) compared to observations from multiple sites, which can lead to problems in regional and global modeling. Among the explicitly modeled VOCs, the precursor compounds that contribute the greatest SOA mass are methylbenzenes. Polycyclic aromatic hydrocarbons (PAHs) are less important precursors and contribute less than 4% of the SOA mass. The amounts of SOA mass from diesel vehicles, gasoline vehicles, and cooking emissions are estimated to be 16–27, 35–61, and 19–35%, respectively, depending on the parameterization used, which is consistent with the observed fossil fraction of urban SOA, 71 (±3) %. In-basin biogenic VOCs are predicted to contribute only a few percent to SOA. A regional SOA background of approximately 2.1 μg m−3 is also present due to the long distance transport of highly aged OA. The percentage of SOA from diesel vehicle emissions is the same, within the estimated uncertainty, as reported in previous work that analyzed the weekly cycles in OA concentrations (Bahreini et al., 2012; Hayes et al., 2013). However, the modeling work presented here suggests a strong anthropogenic source of modern carbon in SOA, due to cooking emissions, which was not accounted for in those previous studies. Lastly, this work adapts a simple two-parameter model to predict SOA concentration and O/C from urban emissions. This model successfully predicts SOA concentration, and the optimal parameter combination is very similar to that found for Mexico City. This approach provides a computationally inexpensive method for predicting urban SOA in global and climate models. We estimate pollution SOA to account for 26 Tg yr−1 of SOA globally, or 17% of global SOA, 1/3 of which is likely to be non-fossil.

Description: Petroleum and dairy operations are prominent sources of gas-phase organic compounds in California's San Joaquin Valley. Ground site measurements in Bakersfield and aircraft measurements of reactive gas-phase organic compounds were made in this region as part of the CalNex (California Research at the Nexus of Air Quality and Climate Change) project to determine the sources contributing to regional gas-phase organic carbon emissions. Using a combination of near-source and downwind data, we assess the composition and magnitude of emissions from these prominent sources that are relatively understudied compared to motor vehicles We also developed a statistical modeling method with the FLEXPART-WRF transport and meteorological model using ground-based data to assess the spatial distribution of emissions in the San Joaquin Valley. We present evidence for large sources of paraffinic hydrocarbons from petroleum extraction/processing operations and oxygenated compounds from dairy (and other cattle) operations. In addition to the small straight-chain alkanes typically associated with petroleum operations, we observed a wide range of branched and cyclic alkanes that have limited previous in situ measurements or characterization in emissions from petroleum operations. Observed dairy emissions were dominated by ethanol, methanol, and acetic acid, and methane. Dairy operations were responsible for the vast majority of methane emissions in the San Joaquin Valley; observations of methane were well-correlated with non-vehicular ethanol, and multiple assessments of the spatial distribution of emissions in the San Joaquin Valley highlight the dominance of dairy operations for methane emissions. The good agreement of the observed petroleum operations source profile with the measured composition of non-methane hydrocarbons in unrefined natural gas associated with crude oil suggests a fugitive emissions pathway during petroleum extraction, storage, or processing with negligible coincident methane emissions Aircraft observations of emission hotspots from operations at oil wells and dairies are consistent with the statistical source footprint determined via transport modeling and ground-based data. At Bakersfield, petroleum and dairy operations each comprised 22–23% of anthropogenic non-methane organic carbon and were each responsible for ~12% of potential precursors to ozone, but their direct impacts as potential SOA precursors were estimated to be minor. A comparison with the California Air Resources Board emission inventory supports the current relative emission rates of reactive organic gases from these sources in the region.

Description: The effects of acidic seed aerosols on the formation of secondary organic aerosol (SOA) have been examined in a number of previous studies, several of which have observed strong linear correlations between the aerosol acidity (measured as nmol H+ per m3 air sample volume) and the percent change of secondary organic carbon (SOC). The measurements have used several precursor compounds representative of different classes of biogenic hydrocarbons including isoprene, monoterpenes, and sesquiterpenes. To date, isoprene has displayed the most pronounced increase in SOC, although few measurements have been conducted with anthropogenic hydrocarbons. In the present study, we examine several aspects of the effect of aerosol acidity on the secondary organic carbon formation from the photooxidation of 1,3-butadiene, as well as extending the previous analysis of isoprene. The photooxidation products measured in the absence and presence of acidic sulfate aerosols were generated either through photochemical oxidation of SO2 or by nebulizing mixtures of ammonium sulfate and sulfuric acid into a 14.5 m3 smog chamber system. The results showed that, like isoprene and β-caryophyllene, 1,3-butadiene SOC yields linearly correlate with increasing acidic sulfate aerosol. The observed acid sensitivity of 0.11% SOC increase per nmol m−3 increase in H+ was approximately a factor of three less than that measured for isoprene. The results also showed that the aerosol yield decreased with increasing humidity for both isoprene and 1,3-butadiene, although to different degrees. Increasing the absolute humidity from 2 to 12 g m−3 reduced the 1,3-butadiene yield by 45% and the isoprene yield by 85%.