Reactive nitrogen budget during the NASA SONEX Mission

The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlantic during October/November 1997 offered an excellent opportunity to examine the budget of reactive nitrogen in the upper troposphere (8–12 km altitude). The median measured total reactive nitrogen (NO y ) mixing ratio was 425 parts per trillion by volume (pptv). A data set merged to the HNO 3 measurement time resolution was used to calculate NO y (NO y sum) by summing the reactive nitrogen species (a combination of measured plus modeled results) and comparing it to measured NO y (NO y meas.). Comparisons were done for tropospheric air (O 3 <100 parts per billion by volume (ppbv)) and stratospherically influenced air (O 3 > 100 ppbv) with both showing good agreement between NO y sum and NO y meas. (slope >0.9 and r² ≈ 0.9). The total reactive nitrogen budget in the upper troposphere over the North Atlantic appears to be dominated by a mixture of NO x (NO + NO 2 ), HNO 3 , and PAN. In tropospheric air median values of NO x /NO y were ≈ 0.25, HNO 3 /NO y ≈ 0.35 and PAN/NO y ≈ 0.17. Particulate NO 3 − and alkyl nitrates together composed <10% of NO y , while model estimated HNO 4 averaged 12%. For the air parcels sampled during SONEX, there does not appear to be a large reservoir of unidentified NO y compounds.