Effect of volcanic aerosol on stratospheric NO2 and N2O5 from 2002–2014 as measured by Odin-OSIRIS and Envisat-MIPAS

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Adams, Cristen ; Bourassa, Adam E. ; McLinden, Chris A. ; Sioris, Chris E. ; Clarmann, Thomas ; Funke, Bernd ; Rieger, Landon A. ; Degenstein, Douglas A. (2016)

Following the large volcanic eruptions of Pinatubo in 1991 and El Chichón in 1982, decreases in stratospheric NO<sub>2</sub> associated with enhanced aerosol were observed. The Optical Spectrograph and InfraRed Imaging Spectrometer (OSIRIS) likewise measured widespread enhancements of stratospheric aerosol following seven volcanic eruptions between 2002 and 2014, although the magnitudes of these eruptions were all much smaller than the Pinatubo and El Chichón eruptions. In order to isolate and quantify the relationship between volcanic aerosol and NO<sub>2</sub>, NO<sub>2</sub> anomalies were calculated using measurements from OSIRIS and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). In the tropics, variability due to the quasi-biennial oscillation was subtracted from the timeseries. OSIRIS profile measurements indicate that the strongest relationships between NO<sub>2</sub> and volcanic aerosol extinction were for the layer ~ 3&ndash;7 km above the tropopause, where OSIRIS stratospheric NO<sub>2</sub> partial columns for ~ 3&ndash;7 km above the tropopause were found to be smaller than baseline levels during these aerosol enhancements by up to ~ 60 % with typical Pearson correlation coefficients of R ~ &minus;0.7. MIPAS also observed decreases in NO<sub>2</sub> partial columns during periods of affected by volcanic aerosol, with percent differences of up to ~ 25 %. An even stronger relationship was observed between OSIRIS aerosol optical depth and MIPAS N<sub>2</sub>O<sub>5</sub> partial columns, with R ~ &minus;0.9, although no link with MIPAS HNO<sub>3</sub> was observed. The variation of OSIRIS NO<sub>2</sub> with increasing aerosol was found to be quantitatively consistent with simulations from a photochemical box model in terms of both magnitude and degree of non-linearity.
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