Sulfur dioxide emission flux measurements from point sources using airborne near ultraviolet spectroscopy during the New England Air Quality Study 2004

Abstract

This work presents measurements of sulfur dioxide (SO2) emission fluxes from point sources using airborne near‐ultraviolet (UV) spectroscopy. A Czerny‐Turner spectrograph has been optimized to measure SO2 and the oxygen collision complex (O4) in the wavelength region of 286–408 nm from an aircraft platform. The spectrograph was deployed aboard the NOAA WP‐3D Orion aircraft during the New England Air Quality Study during the summer of 2004. The spectrograph has zenith and nadir field of views, allowing for measurements of pollution plumes when the aircraft is in or above the planetary boundary layer. The near‐UV spectra are analyzed using the differential optical absorption spectroscopy (DOAS) method to retrieve SO2 and O4 differential slant column densities (DSCDs). The SO2 DSCDs are used to identify point source plumes and are converted to vertical column densities (VCDs), which are needed to calculate emissions of SO2 from point sources. The conversion to VCDs requires knowledge of the photon optical path length or the air mass factor (AMF). We present a novel approach to calculate the AMF using observations of the absorption of solar radiation by O4. The SO2 VCDs, wind speed and direction, and aircraft speed are then used to obtain emission fluxes from power plants. The measured SO2 power plant emission fluxes are compared to the reported emissions from the power plants. The measured and reported SO2 emission fluxes are in good agreement.