Urban Impacts On Atmospheric Chemistry: Surface Ozone in Large Versus Small Urban Centers and Urban Pollution in Asian Dust Storms
Maxwell-Meier, Kari Lynn
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In Part 1, we separated surface ozone time series collected from EPA monitoring sites in and around Georgia from 1980-2002 using a Kolmogorov -Zurbenko Filter to assess the influences associated with characteristic timescales to the overall variability of ozone for individual communities. Comparison of time scale variabilities supports that the diurnal and synoptic variation are most influential timescales in small and large urban and rural locations, with the synoptic scale variation decreasing with the increase of urban size. We define boundaries of influence due to a communitys local chemistry and due to transport by utilizing the diurnal and synoptic ozone timescales respectively. We used the synoptic scale to evaluate the boundaries of similarity among sites that share synoptic scale trends due to transport. Results showed two-phased correlation decay with distance from urban centers. We evaluate the diurnal timescale as a means of evaluating the influence of an areas photochemistry, separated from long-range transport mechanisms. We consider isolation of the diurnal timescale extrapolated spatially for a relative sensitivity analysis based on ozone with respect to concentrations of the precursor group NOy. Results show differences base on urban scale and can define photochemical boundaries. In Part 2, a Particle-Into-Liquid Sampler with an anion/cation chromatograph (PILS-IC) was used to evaluate the fine particle desert dust mixed with urban pollution during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia). Three flights in the Yellow Sea boundary layer captured high mineral dust mixed with pollutants from Asian urban centers. Results report on the fine particle ionic compositions and chemical evolution of dust and pollution during those flights. The main component of water-soluble mineral dust was Ca2+ with Mg2+, which existed with significant fractions in the form of carbonates. Nitrate and sulfate measured after transport of nearly half a day, were connected to ammonium or potassium, the rest likely associated with mineral dust. Initial mass accommodation coefficients much less than 0.1 for uptake of SO2 or HNO3 by mineral dust in urban plumes containing fossil fuel and biomass burning emissions could explain the observations. The data suggest a dependence of accommodation coefficient on relative humidity.