Abstract
Abstract. The local and regional impacts of open fires and trash burning on ground-level ozone (O3) and fine carbonaceous aerosols in the Mexico City Metropolitan Area (MCMA) and surrounding region during two high fire periods in March 2006 have been evaluated using WRF-CHEM model. The model captured reasonably well the measurement-derived magnitude and temporal variation of the biomass burning organic aerosol (BBOA), and the simulated impacts of open fires on organic aerosol (OA) were consistent with many observation-based estimates. We did not detect significant effects of open fires and trash burning on surface O3 concentrations in the MCMA and surrounding region. In contrast, they had important influences on OA and elemental carbon (EC), increasing primary OA (POA) by ~60%, secondary OA (SOA) by ~22%, total OA (TOA = POA + SOA) by ~33%, and EC by ~22%, on both the local (urban) and regional scales. Although the emissions of trash burning are substantially lower than those from open fires, trash burning made slightly smaller but comparable contributions to OA as open fires did, and exerted an even higher influence on EC. Of the ~22% enhancement in SOA concentrations (equivalent to a ~15% increase in TOA) simulated, about two third was attributed to the open fires and one-third to the trash burning. On the annual basis and taking the biofuel use emissions into consideration, we estimated that open fires, trash burning and biofuel use together contributed about 60% to the loading of POA, 30% to SOA, and 25% to EC in both the MCMA and its surrounding region, of which the open fires and trash burning contributed about 35% to POA, 18% to SOA, and 15% to EC. The estimates of biomass burning impacts in this study may contain considerable uncertainties due to the uncertainties in their emission estimates in magnitude, temporal and spatial distribution, extrapolations and the nature of spot comparison. More observation and modeling studies are needed to accurately assess the impacts of biomass burning on tropospheric chemistry, regional and global air quality, and climate change.
Highlights
Not detect significant effects of open fires and trash burning on surface O3 concentrations in the MCMA and surrounding region
Biomass burning contributes substantially to the organic aerosol (OA) emissions in the MCMA and its surrounding areas, while their contributions to the aerosol precursors are relatively minor compared to the anthropogenic sources
The emissions of aerosols and aerosol precursors from the open fires were calculated based on emission factors and emission ratios measured during the MILAGRO campaign together with the MODIS fire detection data
Summary
Not detect significant effects of open fires and trash burning on surface O3 concentrations in the MCMA and surrounding region They had important influences on OA and elemental carbon (EC), increasing primary OA. Fast et al (2009) considered open fire emissions and compared their modeled POA to airborne measurements of POA They concluded that the BB emissions of some large fires may be overestimated and that the timing of the biomass burning OA was not well simulated. The results indicate that the BB impact on the atmospheric composition, OA, is highly variable with large variations between different estimates This is likely due to several factors, such as the use of different apportionment approaches and their associated limitations, difficulties in estimating the amount of biomass burned, emission characterization, and emission factors, etc.
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