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Fast size-resolved aerosol composition measurements in Mexico City with an AMS.

Jimenez JL; Dzepina K; Dunn M; DeCarlo P; Zhang Q; Huffman A; Salcedo D; Onasch T; Worsnop DR; Mortimer P; Jayne JT; Canagaratna MR; Cardenas B; Volkamer R; de Foy B; Johnson K; Zuberi B; Molina M; Molina L; Smith J; McMurry P; Gaffney J; Marley N
Proceedings of the AAAR 23rd Annual Conference, October 4-8, 2004, Atlanta, Georgia. Mount Laurel, NJ: American Association for Aerosol Research, 2004 Oct; :283
An Aerodyne Aerosol Mass Spectrometer (AMS) was deployed to the CENICA Supersite in Mexico City during the Mexico City Metropolitan Area (MCMA-2003) field study from March 29-May 4, 2003. A nano-SMPS was also deployed at CENICA during the later part of that period. The AMS provided real-time information on mass concentrations of chemical species in/on submicron aerosols, as well as on chemically resolved size distributions, with 4-minute time resolution. The AMS mass concentration compares well with that calculated from the volume concentration of a collocated OPC (LASAIR) and the density estimated from the AMS composition. The non-refractory submicron aerosol mass (approximately PM 1.0) at the CENICA Supersite was comprised of about 2/3 organic carbon and 1/3 inorganic species. A recently developed procedure (Zhang et al., this conference) was applied to estimate the fraction of the organic aerosol that is combustion origin (approximately 1/3 of organic mass) vs. oxygenated (approximately 2/3). Two periods with very different organic mass loadings were identified before and after the holy week and associated holiday period, and during the holiday period. The main inorganic species were ammonium sulfate and ammonium nitrate, with a smaller contribution of ammonium chloride. Intense secondary aerosol formation was observed most days, which is consistent with the high levels of aerosol precursors, radiation, and of radicals (OH, HO2) measured by other researchers at the site. Specifically, many days started with rapid nitrate and SOA formation and deposition onto the aerosol. A case study day for secondary aerosol formation (April 9th, 2003) will be presented. Particulate sulfate is mostly advected to this site, rather than locally formed. Both vertical mixing (mixing layer dynamics) and horizontal advection also play important roles in the concentrations observed at this site. The aerosol size distribution was often bimodal (in Dva), with a smaller mode centered around 100 nm (characteristic of traffic emissions) and a larger accumulation mode around 400-600 nm. Condensation of secondary species was observed on both modes, an observation confirmed by electron microscopy. The combined AMS and SMPS data reveal two main sources of ultra fine aerosol in the city: sulfate-dominated new particle formation, and traffic emissions. A beam width probe was used during the 2003 deployment to probe the shape and mixing state of the particles and to improve the absolute quantification capabilities of the AMS. Results from this probe indicate that the collection efficiency (CE) of the AMS was approximately 100% for all species during this campaign. We speculate that the large concentrations of ammonium nitrate and secondary organics may have resulted in nearly spherical particles during this campaign.
Aerosols; Aerosol-particles; Nitrates; Aerosol-sampling; Mass-spectrometry; Organic-dusts; Organic-compounds; Nanotechnology
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Work Environment and Workforce: Mixed Exposures
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Proceedings of the AAAR 23rd Annual Conference, October 4-8, 2004, Atlanta, Georgia
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University of Cincinnati, Cincinnati, Ohio
Page last reviewed: January 27, 2023
Content source: National Institute for Occupational Safety and Health Education and Information Division