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A multispecies approach to investigate the changing cocktail of atmospheric urban carbon

Urban atmospheric carbon is emitted from a variety of sources typically including carbon dioxide (CO2), methane (CH4), volatile organic compounds (VOCs), and organic aerosols. Urban carbon from a myriad of biogenic and anthropogenic sources can typically be identified by their VOC emission signatures (e.g. fossil-fuel based transport, cooking, consumer products, industrial activities, etc.), but the mixture of sources and chemical composition is rapidly changing. In particular, US vehicular emissions have been dramatically decreasing since the 1970s due to air pollution regulations. Further decreases are now also occurring due to a shift towards electric vehicles. The relative contribution of volatile chemical products (VCPs), cooking emissions, and other indoor sources, to urban emissions is growing. Additionally, emissions from organic waste management may also be increasing as a result of policies meant to reduce CH4 production in landfills, as elucidated more fully below. Unfortunately, many important sources of VCPs and other VOC emissions are not targeted by air pollution regulation efforts, and thus emission inventories are extremely uncertain. VOCs are the fuel of atmospheric chemistry leading to secondary formation of urban ozone and particulate matter. Even with the massive reductions in emissions from vehicles and other regulated sources, ozone and particulate matter levels still frequently exceed current air pollution standards in US urban areas. Further reductions in greenhouse gases and improvements in urban air quality require regulations based on a better understanding of the evolving chemical cocktail of urban carbon emissions.
We propose to investigate emerging changes in urban carbon emissions resulting from mitigation strategies being implemented through state and local regulations. Urban sources of major interests include the evolving composting and sewage treatment facilities, indoor sources, cooking, VCPs, and urban vegetation, as vehicle emissions continue to decline. The research will take a multispecies approach to understanding urban sources, where VOC speciation can identify chemical source signatures. We will utilize a mobile van owned and operated by the Bay Area Air Quality Management District (BAAQMD, with in kind support provided) which includes fast measurements for CO2, CH4, �13CH4, C2H6, N2O, and CO. We will add fast measurements of VOCs using a recently acquired VOCUS instrument. Measurement strategies will include: -Mobile observations at regular intervals in the domain of an existing fixed sensor network (BEACO2N) in the San Francisco Bay Area of California, and the broader network of observations by the BAAQMD, to establish the spatial and temporal distribution of hot spots for emissions, their chemical cocktail signatures, then to quantify and categorize source contributions of urban carbon. -Targeted studies of emissions from organic waste composting facilities, landfills, and anaerobic digesters using standalone dry-digestion and at wastewater treatment plants, to measure chemical signatures, and build the knowledge base to estimate contributions to emission inventories in the SF Bay Area. -Fixed flux measurements at a specific location of interest within the SF Bay area (with study site based on results from the mobile observations and fixed sensor networks) to establish temporal variability in emission and deposition rates and elucidate processes driving them

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