Effect of volcanic aerosol on stratospheric NO2 and N2O5 from 2002–2014 as measured by Odin-OSIRIS and Envisat-MIPAS
Atmospheric Chemistry and Physics
<p><strong>Abstract.</strong> 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) measured the 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.
... 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 time series. OSIRIS profile measurements indicate that the strongest anticorrelations between NO<sub>2</sub> and volcanic aerosol extinction were for the 5<span class="thinspace"></span>km layer starting ∼ <span class="thinspace"></span>3<span class="thinspace"></span>km above the climatological mean tropopause at the given latitude. OSIRIS stratospheric NO<sub>2</sub> partial columns in this layer were found to be smaller than background NO<sub>2</sub> levels during these aerosol enhancements by up to ∼ <span class="thinspace"></span>60<span class="thinspace"></span>% with typical Pearson correlation coefficients of <i>R</i> ∼ −0. 7. MIPAS also observed decreases in NO<sub>2</sub> partial columns during periods affected by volcanic aerosol, with percent differences of up to ∼ <span class="thinspace"></span>25<span class="thinspace"></span>% relative to background levels. An even stronger anticorrelation was observed between OSIRIS aerosol optical depth and MIPAS N<sub>2</sub>O<sub>5</sub> partial columns, with <i>R</i> ∼ −0. 9, although no link with MIPAS HNO<sub>3</sub> was observed. The variation in OSIRIS NO<sub>2</sub> with increasing aerosol was found to be consistent with simulations from a photochemical box model within the estimated model uncertainty.</p>