Reactive nitrogen budget during the NASA SONEX mission

The SASS Ozone and Nitrogen Oxides Experiment (SONEX) over the North Atlant ic during October/November 1997 offered an excellent opportunity to examine the budget of reactive nitrogen in the upper troposphere (8 - 12 km altitu de). The median measured total reactive nitrogen (NO,) mixing ratio was 425 parts per trillion by volume (pptv). A data set merged to the HNO3 measure ment time resolution was used to calculate NOy (NOy sum) by summing the rea ctive nitrogen species (a combination of measured plus modeled results) and comparing it to measured NOy (NOy meas.). Comparisons were done for tropos pheric air (O-3 <100 parts per billion by volume (ppbv)) and stratospherica lly influenced air (O-3 > 100 ppbv) with both showing good agreement betwee n NOy sum and NOy meas. (slope >0.9 and r(2) approximate to 0.9). The total reactive nitrogen budget in the upper troposphere over the North Atlantic appears to be dominated by a mixture of NOx (NO + NO2), HNO3, and PAN. In t ropospheric air median values of NOx/NOy were approximate to 0.25, HNO3/NOy approximate to 0.35 and PAN/NOy approximate to 0.17. Particulate NO3- and alkyl nitrates together composed <10% of NOy, while model estimated HNO4 av eraged 12%. For the air parcels sampled during SONEX, there does not appear to be a large reservoir of unidentified NOy compounds.