scholarly journals Impact of a large wildfire on water-soluble organic aerosol in a major urban area: the 2009 Station Fire in Los Angeles County

2011 ◽  
Vol 11 (4) ◽  
pp. 12849-12887 ◽  
Author(s):  
A. Wonaschütz ◽  
S. P. Hersey ◽  
A. Sorooshian ◽  
J. S. Craven ◽  
A. R. Metcalf ◽  
...  
Keyword(s):  
Los Angeles ◽  
Organic Carbon ◽  
Urban Area ◽  
Sea Breeze ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Organic Mass ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Photochemical Aging

Abstract. Water-soluble organic carbon is a major component of aerosol particles globally. This study examines a field dataset of water-soluble organic aerosol in the Los Angeles Basin, a classic urban setting, under typical conditions and under the influence of a large wildfire (the 2009 Station Fire). The measurements took place between July and September in Pasadena as part of the 2009 Pasadena Aerosol Characterization Observatory (PACO) field campaign. Large differences in the nature of water-soluble organic carbon (WSOC) were observed between periods with and without the influence of the fire. During non-fire periods, WSOC variability was driven most likely by a combination of photochemical production processes and subsequent sea breeze transport, resulting in an average diurnal cycle with a maximum at 15:00 LT (up to 4.9 μg C m−3). During the Station Fire, smoke plumes advected to the site in the morning hours were characterized by high concentrations of WSOC (up to 41 μg C m−3) in tight correlation with nitrate and chloride, and with Aerodyne Aerosol Mass Spectrometer (AMS) organic metrics such as the biomass burning tracer m/z 60, and total non-refractory organic mass. These concentrations and correlations and the proximity of the measurement site to the fire suggest that primary production was a key formation mechanism for WSOC. During the afternoons, the sea breeze transported urban pollution and processed residual smoke back to the measurement site, leading to higher afternoon WSOC levels than on non-fire days. Parameters representing higher degrees of oxidation of organics, including the ratios m/z 44 : m/z 57 and m/z 44 : m/z 43, were increased in those air masses. Intercomparisons of relative amounts of WSOC, AMS organic, m/z 44, and m/z 43 are used to examine how the relative abundance of different classes of WSOC species changed as a result of photochemical aging. The fraction of WSOC comprised of acid-oxygenates increased as a of photochemical aging owing to the conversion of aliphatic and non-acid oxygenated organics to more acid-like organics. Assuming a factor of 1.8 to convert WSOC concentrations to organic mass-equivalent concentrations, the contribution of water-soluble organic species to the organic mass budget (10th–90th percentile values) ranged between 27–72% and 27–68% during fire and non-fire periods, respectively. Therefore, WSOC is a significant contributor to the organic aerosol budget in this urban area. The influence of fires in this basin greatly enhances the importance of this class of organics, which has implications for the radiative and hygroscopic properties of the regional aerosol.

scholarly journals Impact of a large wildfire on water-soluble organic aerosol in a major urban area: the 2009 Station Fire in Los Angeles County

2011 ◽  
Vol 11 (16) ◽  
pp. 8257-8270 ◽  
Author(s):  
A. Wonaschütz ◽  
S. P. Hersey ◽  
A. Sorooshian ◽  
J. S. Craven ◽  
A. R. Metcalf ◽  
...  
Keyword(s):  
Los Angeles ◽  
Sea Breeze ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Organic Mass ◽  
Seasonal Incidence ◽  
Mass Spectral ◽  
Hygroscopic Properties ◽  
High Concentrations ◽  
Photochemical Aging

Abstract. This study examines the nature of water-soluble organic aerosol measured in Pasadena, CA, under typical conditions and under the influence of a large wildfire (the 2009 Station Fire). During non-fire periods, water-soluble organic carbon (WSOC) variability was driven by photochemical production processes and sea breeze transport, resulting in an average diurnal cycle with a maximum at 15:00 local time (up to 4.9 μg C m−3). During the Station Fire, primary production was a key formation mechanism for WSOC. High concentrations of WSOC (up to 41 μg C m−3) in smoke plumes advected to the site in the morning hours were tightly correlated with nitrate and chloride, numerous aerosol mass spectrometer (AMS) organic mass spectral markers, and total non-refractory organic mass. Processed residual smoke was transported to the measurement site by the sea breeze later in the day, leading to higher afternoon WSOC levels than on non-fire days. Parameters representing higher degrees of oxidation of organics, including the ratios of the organic metrics m/z 44:m/z 57 and m/z 44:m/z 43, were elevated in those air masses. Intercomparisons of relative amounts of WSOC, organics, m/z 44, and m/z 43 show that the fraction of WSOC comprising acid-oxygenates increased as a function of photochemical aging owing to the conversion of aliphatic and non-acid oxygenated organics to more acid-like organics. The contribution of water-soluble organic species to the organic mass budget (10th–90th percentile values) ranged between 27 %–72 % and 27 %–68 % during fire and non-fire periods, respectively. The seasonal incidence of wildfires in the Los Angeles Basin greatly enhances the importance of water-soluble organics, which has implications for the radiative and hygroscopic properties of the regional aerosol.

scholarly journals Mass absorption efficiency of elemental carbon and water-soluble organic carbon in Beijing, China

2011 ◽  
Vol 11 (22) ◽  
pp. 11497-11510 ◽  
Author(s):  
Y. Cheng ◽  
K.-B. He ◽  
M. Zheng ◽  
F.-K. Duan ◽  
Z.-Y. Du ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Biomass Burning ◽  
Light Absorption ◽  
Elemental Carbon ◽  
Organic Aerosol ◽  
Absorption Efficiency ◽  
Water Soluble ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Mass Absorption Efficiency

Abstract. The mass absorption efficiency (MAE) of elemental carbon (EC) in Beijing was quantified using a thermal-optical carbon analyzer. The MAE measured at 632 nm was 8.45±1.71 and 9.41±1.92 m2 g−1 during winter and summer respectively. The daily variation of MAE was found to coincide with the abundance of organic carbon (OC), especially the OC to EC ratio, perhaps due to the enhancement by coating with organic aerosol (especially secondary organic aerosol, SOA) or the artifacts resulting from the redistribution of liquid-like organic particles during the filter-based absorption measurements. Using a converting approach that accounts for the discrepancy caused by measurements methods of both light absorption and EC concentration, previously published MAE values were converted to the equivalent-MAE, which is the estimated value if using the same measurement methods as used in this study. The equivalent-MAE was found to be much lower in the regions heavily impacted by biomass burning (e.g., below 2.7 m2 g−1 for two Indian cities). Results from source samples (including diesel exhaust samples and biomass smoke samples) also demonstrated that emissions from biomass burning would decrease the MAE of EC. Moreover, optical properties of water-soluble organic carbon (WSOC) in Beijing were presented. Light absorption by WSOC exhibited strong wavelength (λ) dependence such that absorption varied approximately as λ−7, which was characteristic of the brown carbon spectra. The MAE of WSOC (measured at 365 nm) was 1.79±0.24 and 0.71±0.20 m2 g−1 during winter and summer respectively. The large discrepancy between the MAE of WSOC during winter and summer was attributed to the difference in the precursors of SOA such that anthropogenic volatile organic compounds (AVOCs) should be more important as the precursors of SOA in winter. The MAE of WSOC in Beijing was much higher than results from the southeastern United States which were obtained using the same method as used in this study, perhaps due to the stronger emissions of biomass burning in China.

scholarly journals Functional characterization of the water-soluble organic carbon of size-fractionated aerosol in the southern Mississippi Valley

2014 ◽  
Vol 14 (12) ◽  
pp. 6075-6088 ◽  
Author(s):  
M.-C. G. Chalbot ◽  
J. Brown ◽  
P. Chitranshi ◽  
G. Gamboa da Costa ◽  
E. D. Pollock ◽  
...  
Keyword(s):  
Organic Carbon ◽  
1H Nmr ◽  
Biomass Burning ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Particle Mass ◽  
Proton Nuclear Magnetic Resonance ◽  
Relative Distribution ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon

Abstract. The chemical content of water-soluble organic carbon (WSOC) as a function of particle size was characterized in Little Rock, Arkansas in winter and spring 2013. The objectives of this study were to (i) compare the functional characteristics of coarse, fine and ultrafine WSOC and (ii) reconcile the sources of WSOC for periods when carbonaceous aerosol was the most abundant particulate component. The WSOC accounted for 5% of particle mass for particles with dp > 0.96 μm and 10% of particle mass for particles with dp < 0.96 μm. Non-exchangeable aliphatic (H–C), unsaturated aliphatic (H–C–C=), oxygenated saturated aliphatic (H–C–O), acetalic (O–CH–O) and aromatic (Ar–H) protons were determined by proton nuclear magnetic resonance (1H-NMR). The total non-exchangeable organic hydrogen concentrations varied from 4.1 ± 0.1 nmol m−3 for particles with 1.5 < dp < 3.0 μm to 73.9 ± 12.3 nmol m−3 for particles with dp < 0.49 μm. The molar H / C ratios varied from 0.48 ± 0.05 to 0.92 ± 0.09, which were comparable to those observed for combustion-related organic aerosol. The R–H was the most abundant group, representing about 45% of measured total non-exchangeable organic hydrogen concentrations, followed by H–C–O (27%) and H–C–C= (26%). Levoglucosan, amines, ammonium and methanesulfonate were identified in NMR fingerprints of fine particles. Sucrose, fructose, glucose, formate and acetate were associated with coarse particles. These qualitative differences of 1H-NMR profiles for different particle sizes indicated the possible contribution of biological aerosols and a mixture of aliphatic and oxygenated compounds from biomass burning and traffic exhausts. The concurrent presence of ammonium and amines also suggested the presence of ammonium/aminium nitrate and sulfate secondary aerosol. The size-dependent origin of WSOC was further corroborated by the increasing δ13C abundance from −26.81 ± 0.18‰ for the smallest particles to −25.93 ± 0.31‰ for the largest particles and the relative distribution of the functional groups as compared to those previously observed for marine, biomass burning and secondary organic aerosol. The latter also allowed for the differentiation of urban combustion-related aerosol and biological particles. The five types of organic hydrogen accounted for the majority of WSOC for particles with dp > 3.0 μm and dp < 0.96 μm.

scholarly journals Spatial and seasonal variations of fine particle water-soluble organic carbon (WSOC) over the Southeastern United States: implications for secondary organic aerosol formation

2012 ◽  
Vol 12 (4) ◽  
pp. 9621-9664 ◽  
Author(s):  
X. Zhang ◽  
Z. Liu ◽  
A. Hecobian ◽  
M. Zheng ◽  
N. H. Frank ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Fine Particles ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Aerosol Formation ◽  
Southeastern Us ◽  
Urban Rural ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon

Abstract. Secondary organic aerosol (SOA) in the Southeastern US is investigated by analyzing the spatial-temporal distribution of water-soluble organic carbon (WSOC) and other PM2.5 components from 900 archived 24 h Teflon filters collected at 15 urban or rural EPA Federal Reference Method (FRM) network sites throughout 2007. Online measurements of WSOC at an urban/rural-paired site in Georgia in the summer of 2008 are contrasted to the filter data. Based on FRM filters, excluding biomass-burning events (levoglucosan < 50 ng m−3), WSOC and sulfate were highly correlated with PM2.5 mass and both comprised a large mass fraction of PM2.5 (13% and 35%, respectively). Sulfate and WSOC both tracked ambient temperature throughout the year, suggesting the temperature effects were mainly on the photochemical processes that lead to secondary formation. FRM WSOC, and to a lesser extent sulfate, were spatially homogeneous throughout the region, yet WSOC was moderately enhanced (27%) in locations of greater predicted isoprene emissions in summer. A Positive Matrix Factorization (PMF) analysis identified two major source types for the summer WSOC; 22% of the WSOC were associated with ammonium sulfate, and 56% of the WSOC was associated with brown carbon and oxalate. A small urban excess of FRM WSOC (10%) was observed in the summer of 2007, however, comparisons of online WSOC measurements at one urban/rural pair (Atlanta/Yorkville) in August 2008 showed substantially greater difference in WSOC (31%) relative to the FRM data, suggesting a low bias for urban filters. The measured Atlanta urban excess, combined with the estimated boundary layer heights, gave an estimated Atlanta daily WSOC production rate in August of 0.55 mg C m−2 h−1 between mid-morning and mid-afternoon. This study characterizes the regional nature of fine particles in the Southeastern US, confirming the importance of secondary organic aerosol and the roles of both biogenic and anthropogenic emissions.

scholarly journals Spatial and seasonal variations of fine particle water-soluble organic carbon (WSOC) over the southeastern United States: implications for secondary organic aerosol formation

2012 ◽  
Vol 12 (14) ◽  
pp. 6593-6607 ◽  
Author(s):  
X. Zhang ◽  
Z. Liu ◽  
A. Hecobian ◽  
M. Zheng ◽  
N. H. Frank ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Ammonium Sulfate ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Aerosol Formation ◽  
Southeastern Us ◽  
Urban Rural ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon

Abstract. Secondary organic aerosol (SOA) in the southeastern US is investigated by analyzing the spatial-temporal distribution of water-soluble organic carbon (WSOC) and other PM2.5 components from 900 archived 24-h Teflon filters collected at 15 urban or rural EPA Federal Reference Method (FRM) network sites throughout 2007. Online measurements of WSOC at an urban/rural-paired site in Georgia in the summer of 2008 are contrasted to the filter data. Based on FRM filters, excluding biomass-burning events (levoglucosan < 50 ng m−3), WSOC and sulfate were highly correlated with PM2.5 mass (r2~0.7). Both components comprised a large mass fraction of PM2.5 (13% and 31%, respectively, or ~25% and 50% for WSOM and ammonium sulfate). Sulfate and WSOC both tracked ambient temperature throughout the year, suggesting the temperature effects were mainly linked to faster photochemistry and/or synoptic meteorology and less due to enhanced biogenic hydrocarbon emissions. FRM WSOC, and to a lesser extent sulfate, were spatially homogeneous throughout the region, yet WSOC was moderately enhanced (27%) in locations of greater predicted isoprene emissions in summer. A Positive Matrix Factorization (PMF) analysis identified two major source types for the summer WSOC; 22% of the WSOC were associated with ammonium sulfate, and 56% of the WSOC were associated with brown carbon and oxalate. A small urban excess of FRM WSOC (10%) was observed in the summer of 2007, however, comparisons of online WSOC measurements at one urban/rural pair (Atlanta/Yorkville) in August 2008 showed substantially greater difference in WSOC (31%) relative to the FRM data, suggesting a low bias for urban filters. The measured Atlanta urban excess, combined with the estimated boundary layer heights, gave an estimated Atlanta daily WSOC production rate in August of 0.55 mgC m−2 h−1 between mid-morning and mid-afternoon. This study characterizes the regional nature of fine particles in the southeastern US, confirming the importance of SOA and the roles of both biogenic and anthropogenic emissions.

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