Aircraft-based ultraviolet spectroscopy measurements of sulfur dioxide emissions from point sources

Accurate measurements of sulfur dioxide (SO2) emissions from point sources are important in urban air pollution studies due to the human health and environmental effects of SO2. The human health effects of SO2 include respiratory illnesses and aggravation of existing heart and lung diseases. The environmental effects of SO2 include the formation of acid rain and sulfate particles. This work presents a novel approach to accurately measuring SO2 emissions from point sources using aircraft-based ultraviolet spectroscopy. A Czerny-Turner style spectrograph has been optimized to measure SO2 in the ultraviolet wavelength region from an aircraft platform. The spectrograph has zenith and nadir field of views allowing for measurements of the pollution plume independent of the aircraft altitude and the height and uniformity of the boundary layer. The spectrograph has a 1200 lines/mm grating and a 50 mum entrance slit width resulting in an optical resolution of 0.33 nm in the 289 to 410 nm wavelength region. A short integration time yields a high frequency measurement in order to distinguish localized pollution plume from surrounding air. The spectrograph was deployed aboard the NOAA WP-3D aircraft during the New England Air Quality Study during the summer of 2004 (NEAQS2K4). The ultraviolet spectra are analyzed using the differential optical absorption spectroscopy (DOAS) method to retrieve SO2 differential slant column densities (dSCD). The SO2 dSDC are used to obtain emission fluxes from point sources.