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1.
Modeling the multiday evolution and aging of secondary organic aerosol during MILAGRO 2006
Jose L. Jimenez, Peter F. DeCarlo, Rahul A. Zaveri, Katja Džepina, Christopher D. Cappa, Rainer Volkamer, Sasha Madronich, 2011, original scientific article

Abstract: In this study, we apply several recently proposed models to the evolution of secondary organic aerosols (SOA) and organic gases advected from downtown Mexico City at: an altitude of similar to 3.5 km during three days of aging, in a way that is directly comparable to simulations in regional and global models. We constrain the model with and compare its results to available observations. The model SOA formed from oxidation of volatile organic compounds (V-SOA) when using a non-aging SOA parameterization cannot explain the observed SOA concentrations in aged pollution, despite the increasing importance of the low-NO, channel. However, when using an aging SOA parameterization, V-SOA alone is similar to the regional aircraft observations, highlighting the wide diversity in current V-SOA formulations. When the SOA formed from oxidation of semivolatile and intermediate volatility organic vapors (SI-SOA) is computed following Robinson et al. (2007) the model matches the observed SOA mass, but its 0/C is similar to 2 x too low. With the parameterization of Grieshop et al. (2009), the total SOA mass is similar to 2 x too high, but 0/C and volatility are closer to the observations. Heating or dilution cause the evaporation of a substantial fraction of the model SOA; this fraction is reduced by aging although differently for heating vs dilution. Lifting of the airmass to the free-troposphere during dry convection substantially increases SOA by condensation of semivolatile vapors; this effect is reduced by aging.
Found in: osebi
Keywords: Mexico-city, volatility, semivolatile, transport, campaign
Published: 11.04.2021; Views: 263; Downloads: 0
.pdf Fulltext (3,95 MB)

2.
Characterization of ambient aerosols in Mexico City during the MCMA-2003 campaign with aerosol mass spectrometry
Dara Salcedo, T. B. Onasch, Katja Džepina, M. R. Canagaratna, Qi Zhang, J. A. Huffman, P. F. DeCarlo, J. Jayne, P. Mortimer, D. Worsnop, 2006, original scientific article

Abstract: An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed at the CENICA Supersite, during the Mexico City Metropolitan Area field study (MCMA-2003) from 31 March-4 May 2003 to investigate particle concentrations, sources, and processes. The AMS provides real time information on mass concentration and composition of the non-refractory species in particulate matter less than 1 mu m (NR-PM1) with high time and size-resolution. In order to account for the refractory material in the aerosol, we also present estimates of Black Carbon (BC) using an aethalometer and an estimate of the aerosol soil component obtained from Proton-Induced X-ray Emission Spectrometry (PIXE) analysis of impactor substrates. Comparisons of AMS + BC + soil mass concentration with other collocated particle instruments (a LASAIR Optical Particle Counter, a PM2.5 Tapered Element Oscillating Microbalance (TEOM), and a PM2.5 DustTrak Aerosol Monitor) show that the AMS + BC + soil mass concentration is consistent with the total PM2.5 mass concentration during MCMA-2003 within the combined uncertainties. In Mexico City, the organic fraction of the estimated PM2.5 at CENICA represents, on average, 54.6% (standard deviation sigma=10%) of the mass, with the rest consisting of inorganic compounds ( mainly ammonium nitrate and sulfate/ammonium salts), BC, and soil. Inorganic compounds represent 27.5% of PM2.5 (sigma=10%); BC mass concentration is about 11% (sigma=4%); while soil represents about 6.9% (sigma=4%). Size distributions are presented for the AMS species; they show an accumulation mode that contains mainly oxygenated organic and secondary inorganic compounds. The organic size distributions also contain a small organic particle mode that is likely indicative of fresh traffic emissions; small particle modes exist for the inorganic species as well. Evidence suggests that the organic and inorganic species are not always internally mixed, especially in the small modes. The aerosol seems to be neutralized most of the time; however, there were some periods when there was not enough ammonium to completely neutralize the nitrate, chloride and sulfate present. The diurnal cycle and size distributions of nitrate suggest local photochemical production. On the other hand, sulfate appears to be produced on a regional scale. There are indications of new particle formation and growth events when concentrations of SO2 were high. Although the sources of chloride are not clear, this species seems to condense as ammonium chloride early in the morning and to evaporate as the temperature increases and RH decreases. The total and speciated mass concentrations and diurnal cycles measured during MCMA-2003 are similar to measurements during a previous field campaign at a nearby location.
Found in: osebi
Keywords: aerosol mass-spectrometer, atmospheric aerosol, atmospheric chemistry, atmospheric physics
Published: 12.04.2021; Views: 331; Downloads: 0
.pdf Fulltext (2,53 MB)

3.
Evolution of organic aerosols in the atmosphere
J. H. Kroll, P. F. DeCarlo, J. David Allan, H. Coe, Katja Džepina, Jose L. Jimenez, M. R. Canagaratna, N. M. Donahue, A. S. H. Prevot, Q. Zhang, 2009, original scientific article

Abstract: Organic aerosol (OA) particles affect climate forcing and human health, but their sources and evolution remain poorly characterized. We present a unifying model framework describing the atmospheric evolution of OA that is constrained by high–time-resolution measurements of its composition, volatility, and oxidation state. OA and OA precursor gases evolve by becoming increasingly oxidized, less volatile, and more hygroscopic, leading to the formation of oxygenated organic aerosol (OOA), with concentrations comparable to those of sulfate aerosol throughout the Northern Hemisphere. Our model framework captures the dynamic aging behavior observed in both the atmosphere and laboratory: It can serve as a basis for improving parameterizations in regional and global models.
Found in: osebi
Keywords: secondary organic aerosol, source apportionment, aerodyne aerosol mass spectrometer, global field measurements, laboratory experiments
Published: 11.04.2021; Views: 276; Downloads: 0
.pdf Fulltext (721,30 KB)

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