The seasonal cycle of nitrogen oxides in the Arctic troposphere at Barrow, Alaska

Abstract

Ground level concentrations of total reactive nitrogen (NOy) and NO in the Arctic troposphere were measured at the National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory site at Barrow, Alaska, from March–November, 1990. After screening out impacts from local and regional pollution sources, a well‐defined seasonal cycle of background NOy concentrations is apparent. Concentrations of 560–620 parts per thousand by volume (pptv) during early spring decayed sharply during April and May to extremely low summertime values (median 70 pptv). NO concentrations were < 8 pptv during most background measurements. However, a pulse of NO to ∼35 pptv (maximum hourly average) occurred coincidentally with the NOy decay. Decomposition of peroxyacetyl nitrate (PAN) (and perhaps other reservoir NOy species) due to increasing temperatures and/or insolation in late spring may have caused this NO pulse. Furthermore, by converting NOy from a stable reservoir species (PAN) to a more reactive form (NOx), PAN decomposition is believed to have contributed to the observed NOy decay through formation and deposition of HNO3. Through this process of NOx release in response to warming temperatures, the springtime Arctic NOy reservoir may affect springtime O3 levels both in the Arctic and in the northern mid‐latitudes. During summer, higher NOy and NO concentrations were observed during periods of flow off the inland tundra as compared to marine flow periods, suggesting greater vertical mixing over land. Synoptic flow patterns and diurnal changes had minimal effects on background NOy concentrations. NOy and O3 concentrations were positively correlated during summer, possibly indicating long‐range transport of both and/or the presence of a midtropospheric NOy reservoir combined with a stratospheric O3 source. The data presented and discussed here are compared to the results of modeling studies reporting NOy concentration predictions for the Arctic. Current models have been unable to adequately simulate NOy concentrations and speciation in the Arctic.