Aerosol chemistry and photochemistry in polluted urban environments: research for tomorrow’s megacities

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Although our current understanding of urban air quality comes largely from studies conducted in North America and Western Europe, the bulk of today’s urban growth is occurring in developing Asian and African megacities. The overarching goal of our group's research is to explore light-induced chemistry (photochemistry) that may be promoted in the metal- and soot-rich atmospheric particulate matter (aerosol) typical of developing urban regions and industrially influenced areas, and thus improve our understanding of the processes that govern air quality in these understudied environments. We will explore chemistry and photochemistry at the surface of real, chemically complex aerosol samples, which we will collect in a variety of polluted urban and industrially influenced environments, both in Canada and abroad. In an effort to better understand the influence of aerosol-phase chemistry on the concentrations of trace pollutant gases, we will study the photochemical interactions of O3, NO2 and SO2 with thin films prepared from extracts of these aerosol samples. In addition, we will investigate the possibility that metal-catalyzed photochemistry contributes to the aerosol-phase formation of organosulfate (OS; ROSO3-) and organonitrate (ON; RONO2) compounds, both of which have been shown to contribute significantly to the organic mass present in ambient urban aerosol. We will also work to improve our understanding of the molecular nature and atmospheric consequences of photochemical interactions between dust and urban organic pollutants. Here, we will aim to replicate in the laboratory the processes that deposit organic material on dust aerosol under ambient urban conditions and, by extension, capture the morphological characteristics imprinted on particles by these processes. In an effort to better understand the role that particle morphology plays in influencing reactions at the surface of mixed dust-carbonaceous aerosol, we will compare the photochemical uptake of O3, NO2 and SO2 at the surface of dust aerosol freshly generated from source soils with that at the surface of dust aerosol previously coated with single organic compounds and complex organic mixtures—specifically, exhaust from highly polluting engines typical of those used in developing economies. We will also study dust-pollutant interactions over longer timescales in a newly constructed atmospheric reaction chamber: specifically, we will investigate dust-catalyzed formation of new particles and oxidation of gas-phase organics; in addition, we will investigate the influence of photoactive dust aerosol on the quantity and composition of secondary organic aerosol (SOA) formed from urban organic pollutants.