Source apportionment of fine organic aerosol in Mexico City during the MILAGRO experiment 2006

[摘要] Organic carbon (OC) comprises a large fraction of fine particulate matter(PM_2.5) in Mexico City. Daily and select 12-h PM_2.5 samples werecollected in urban and peripheral sites in Mexico City from 17–30 March2006. Samples were analyzed for OC and elemental carbon (EC) usingthermal-optical filter-based methods. Real-time water-soluble organic carbon(WSOC) was collected at the peripheral site. Organic compounds, particularlymolecular markers, were quantified by soxhlet extraction with methanol anddichloromethane, derivitization, and gas chromatography with massspectrometric detection (GCMS). A chemical mass balance model (CMB) based onmolecular marker species was used to determine the relative contribution ofmajor sources to ambient OC. Motor vehicles, including diesel and gasoline,consistently accounted for 49% of OC in the urban area and 32% on theperiphery. The daily contribution of biomass burning to OC was highlyvariable, and ranged from 5–26% at the urban site and 7–39% at theperipheral site. The remaining OC unapportioned to primary sources showed astrong correlation with WSOC and was considered to be secondary in nature.Comparison of temporally resolved OC showed that contributions from primaryaerosol sources during daylight hours were not significantly different fromnighttime. This study provides quantitative understanding of the importantsources of OC during the MILAGRO 2006 field campaign.

[学科分类] 大气科学