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 HNO3 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 (O3 <100 parts per billion by volume (ppbv)) and stratospherically influenced air (O3>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 + NO2), HNO3, and PAN. In tropospheric air median values of NO(x)/NO(y) were ~0.25, HNO3/NO(y) ~0.35 and PAN/NO(y) ~0.17. Particulate NO3- and alkyl nitrates together composed <10% of NO(y), while model estimated HNO4 averaged 12%. For the air parcels sampled during SONEX, there does not appear to be a large reservoir of unidentified NO(y) compounds