Determining the spatial and seasonal variability in OM/OC ratios across the US using multiple regression

Simon, Heather; Bhave, Prakash V.; Swall, Jenise L.; Frank, N. H.; Malm, William C.

doi:10.5194/acp-11-2933-2011

Cited by 91 publications

(88 citation statements)

References 44 publications

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“…However, the magnitude of OM seasonality is similar between the observations and model with very little variation in OM throughout the year (a 35 % increase in summer over winter), in agreement with values reported by Zhang et al (2012a). The seasonality in OM (and consequently PM 2.5 ) might be enhanced if we used a varying OM/OC ratio, as studies have shown that the ratio is greater in the summer than in the winter (e.g., Simon et al, 2011). However, the ratio would be applied to both the model simulation and observations, and, as GEOS-Chem is already able to simulate the OM seasonality, would therefore not explain the model discrepancy.…”

Section: Seasonality In Aod and Surface Concentrationssupporting

confidence: 75%

Aerosol loading in the Southeastern United States: reconciling surface and satellite observations

Ford

Heald

2013

Atmos. Chem. Phys.

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We investigate the seasonality in aerosols over the Southeastern United States using observations from several satellite instruments (MODIS, MISR, CALIOP) and surface network sites (IMPROVE, SEARCH, AERONET). We find that the strong summertime enhancement in satellite-observed aerosol optical depth (AOD) (factor 2–3 enhancement over wintertime AOD) is not present in surface mass concentrations (25–55% summertime enhancement). Goldstein et al. (2009) previously attributed this seasonality in AOD to biogenic organic aerosol; however, surface observations show that organic aerosol only accounts for ∼35% of fine particulate matter (smaller than 2.5 μm in aerodynamic diameter, PM_2.5) and exhibits similar seasonality to total surface PM_2.5. The GEOS-Chem model generally reproduces these surface aerosol measurements, but underrepresents the AOD seasonality observed by satellites. We show that seasonal differences in water uptake cannot sufficiently explain the magnitude of AOD increase. As CALIOP profiles indicate the presence of additional aerosol in the lower troposphere (below 700 hPa), which cannot be explained by vertical mixing, we conclude that the discrepancy is due to a missing source of aerosols above the surface layer in summer

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Section: Seasonality In Aod and Surface Concentrationssupporting

confidence: 75%

Aerosol loading in the Southeastern United States: reconciling surface and satellite observations

Ford

Heald

2013

Atmos. Chem. Phys.

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“…In these situations the nitrate measured in the fine mode is actually the tail of coarse mode nitrate. POM was computed assuming an average molecular weight per carbon weight for OC of 1.8 based on the work of Malm and Hand [2007], although it is also spatially and temporally variable, and typical values could range from 1.2 to 2.6 [ Turpin and Lim , 2001; El‐Zanan et al , 2005; Malm and Hand , 2007; Malm et al , 2011; Simon et al , 2011]. Although the POM multiplier is most likely lower in urban regions [ Turpin and Lim , 2001; Malm et al , 2011], we applied the same value to data from both networks.…”

Section: Methodsmentioning

confidence: 99%

Seasonal composition of remote and urban fine particulate matter in the United States

et al. 2012

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Speciated aerosol composition data from the rural Interagency Monitoring for Protected Visual Environments (IMPROVE) network and the Environmental Protection Agency's urban/suburban Chemical Speciation Network (CSN) were combined to evaluate and contrast the PM2.5 composition and its seasonal patterns at urban and rural locations throughout the United States. We examined the 2005–2008 monthly and annual mean mass concentrations of PM2.5 ammonium sulfate (AS), ammonium nitrate (AN), particulate organic matter (POM), light‐absorbing carbon (LAC), mineral soil, and sea salt from 168 rural and 176 urban sites. Urban and rural AS concentrations and seasonality were similar, and both were substantially higher in the eastern United States. Urban POM and LAC concentrations were higher than rural concentrations and were associated with very different seasonality depending on location. The highest urban and rural POM and LAC concentrations occurred in the southeastern and northwestern United States. Wintertime peaks in AN were common for both urban and rural sites, but urban concentrations were several times higher, and both were highest in California and the Midwest. Fine soil concentrations were highest in the Southwest, and similar regional patterns and seasonality in urban and rural concentrations suggested impacts from long‐range transport. Contributions from sea salt to the PM2.5 budget were non‐negligible only at coastal sites. This analysis revealed spatial and seasonal variability in urban and rural aerosol concentrations on a continental scale and provided insights into their sources, processes, and lifetimes.

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“…For the oxidation products of the directly emitted species (LVOO1, LVOO2, SVOO1, SVOO2, SVOO3), we have chosen higher OM : OC (and thus lower carbon number) values than Koo et al (2014) to bound the typical observed range of OM : OC reported from ambient studies, including Aiken et al (2008) and Canagaratna et al (2015) for multiple US and global sites (1.3-2.25) and Simon et al (2011) for routine-monitoring networks in the continental US (0.79-2.15). The molecular weights of these species are calculated using the given carbon number and OM : OC, while assuming each representative species comprises only carbon, oxygen, and hydrogen atoms.…”

Section: Poa Semivolatile Partitioning and Agingmentioning

confidence: 99%

Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning

et al. 2017

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Abstract. Mounting evidence from field and laboratory observations coupled with atmospheric model analyses shows that primary combustion emissions of organic compounds dynamically partition between the vapor and particulate phases, especially as near-source emissions dilute and cool to ambient conditions. The most recent version of the Community Multiscale Air Quality model version 5.2 (CMAQv5.2) accounts for the semivolatile partitioning and gas-phase aging of these primary organic aerosol (POA) compounds consistent with experimentally derived parameterizations. We also include a new surrogate species, potential secondary organic aerosol from combustion emissions (pcSOA), which provides a representation of the secondary organic aerosol (SOA) from anthropogenic combustion sources that could be missing from current chemical transport model predictions. The reasons for this missing mass likely include the following: (1) unspeciated semivolatile and intermediate volatility organic compound (SVOC and IVOC, respectively) emissions missing from current inventories, (2) multigenerational aging of organic vapor products from known SOA precursors (e.g., toluene, alkanes), (3) underestimation of SOA yields due to vapor wall losses in smog chamber experiments, and (4) reversible organic compounds-water interactions and/or aqueous-phase processing of known organic vapor emissions. CMAQ predicts the spatially averaged contribution of pcSOA to OA surface concentrations in the continental United States to be 38.6 and 23.6 % in the 2011 winter and summer, respectively.Whereas many past modeling studies focused on a particular measurement campaign, season, location, or model configuration, we endeavor to evaluate the model and important uncertain parameters with a comprehensive set of United States-based model runs using multiple horizontal scales (4 and 12 km), gas-phase chemical mechanisms, July, 2011). Model improvements manifest better correlations (e.g., the correlation coefficient at Pasadena at night increases from 0.38 to 0.62) and reductions in underprediction during the photochemically active afternoon period (e.g., bias at Pasadena from −5.62 to −2.42 µg m −3 ). Daily averaged predictions of observations at routine-monitoring networks from simulations over the continental US (CONUS) in 2011 show modest improvement during winter, with mean biases reducing from 1.14 to 0.73 µg m −3 , but less change in the summer when the decreases from POA evaporation were similar to the magnitude of added SOA mass. Because the model-performance improvement realized by including the relatively simple pcSOA approach is similar to that of more-complicated parameterizations of OA formation and aging, we recommend caution when applying these morecomplicated approaches as they currently rely on numerous uncertain parameters.The pcSOA parameters optimized for performance at the southern and northern California sites lead to higher OA formation than is observed in the CONUS evaluation. This may be due to any of the following: variations in ...

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Determining the spatial and seasonal variability in OM/OC ratios across the US using multiple regression

Cited by 91 publications

References 44 publications

Aerosol loading in the Southeastern United States: reconciling surface and satellite observations

Aerosol loading in the Southeastern United States: reconciling surface and satellite observations

Seasonal composition of remote and urban fine particulate matter in the United States

Semivolatile POA and parameterized total combustion SOA in CMAQv5.2: impacts on source strength and partitioning

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