PAN Among the Peaks: A preliminary analysis of new peroxyacetyl nitrate (PAN) measurements in Rocky Mountain National Park

Abstract:

Several different classes of organic nitrogen compounds are produced when volatile organic compounds (VOCs) are oxidized in the presence of nitrogen oxide radicals (NO_x). The peroxyacyl nitrates and organic nitrates are particularly important as they serve as temporary or permanent sinks for NO_x. PAN (peroxyacetyl nitrate, CH₃C(O)O₂NO₂) is the most important NO_x reservoir, and its eventual decomposition acts as a pathway by which NO_x reaches the remote troposphere. The emissions from oil and gas extraction represent a new VOC regime that could change the local fate of NO_x because the particular mix of VOCs emitted from oil and gas operations should favor PAN formation.

We present new PAN observations from Rocky Mountain National Park (ROMO) for the period 11 July to 15 August. The observations were collected during the Colorado Front Range Air Pollution and Photochemistry Éxperiment (FRAPPÉ). PAN was measured at ROMO with a custom built gas chromatograph with an electron capture detector (GC-ECD). At the time of submission, preliminary campaign mean and maximum PAN mixing ratios were 170 pptv and 1345 pptv respectively. Initial analyses of the data collected to date suggest that the maximum PAN mixing ratios at ROMO occurred on the afternoons of 22 and 23 July. Co-located measurements of VOCs on 22 July indicate that the elevated PAN coincided with elevated abundances light alkanes and other secondary species (O₃ and alkyl nitrates). The ratio of i-pentane to n- pentane (≤1) indicates that this air mass was strongly impacted by oil and gas production operations.