Tropospheric reactive odd nitrogen over the South Pacific in austral springtime

The distribution of reactive nitrogen species over the South Pacific during austral springtime appears to be dominated by biomass burning emissions and possibly lightning and stratospheric inputs. The absence of robust correlations of reactive nitrogen species with source‐specific tracers (e.g., C 2 H 2 [combustion], CH 3 Cl [biomass burning], C 2 Cl 4 [industrial], 210 Pb [continental], and 7 Be [stratospheric]) suggests significant aging and processing of the sampled air parcels due to losses by surface deposition, OH attack, and dilution processes. Classification of the air parcels based on CO enhancements indicates that the greatest influence was found in plumes at 3–8 km altitude in the distributions of HNO 3 and peroxyacetyl nitrate (PAN). Here mixing ratios of these species reached 600 parts per trillion by volume (pptv), values surprisingly large for a location several thousand kilometers removed from the nearest continental areas. The mixing ratio of total reactive nitrogen (the NO y sum), operationally defined in this paper as measured (NO + HNO 3 + PAN + CH 3 ONO 2 + C 2 H 5 ONO 2 ) + modeled (NO 2 ), had a median value of 285 pptv within these plumes compared with 120 pptv in nonplume air parcels. Particle NO − 3 was not included in this analysis of the NO y sum due to its 10‐ to 15‐min sampling time resolution, but, in general, it was <10% of the NO y sum. Comparison of the two air parcel classifications for NO y and alkyl nitrate distributions showed no perceivable plume influence, but recycling of reactive nitrogen may have masked this direct effect. In the marine boundary layer, the NO y sum averaged 50 pptv in both air parcel classifications, being somewhat isolated from the polluted conditions above it by the trade wind inversion. In this region, however, alkyl nitrates appear to have an important marine source where they comprise 20–80% of the NO y sum in equatorial and high‐latitude regions over the South Pacific.