Distribution of reactive nitrogen species in the remote free troposphere: data and model comparisons

The available reactive nitrogen measurements from the global free troposphe re obtained during the period of 1985-1995 have been compiled and analyzed. The species of interest are NO, NOx (NO + NO2), NOy, PAN, HNO3 and O-3. Da ta extending to 13 km have been gridded with a 5 degrees x 5 degrees horizo ntal and 1 km vertical resolution. The data have been divided into two seas ons, namely "Winter" and "Summer" depending upon the time and location of t he observations. Data described here as well as additional analysis have al so been archived and are accessible on-line through the World Wide Web at: http://george.arc.nasa.gov/ similar to athakur. Global maps of the reactive nitrogen species distribution are produced in a form that would be most us eful for the test and evaluation of models of tropospheric transport and ch emistry. Limited comparisons of the observed reactive nitrogen species data with predictions by 3-D global models were performed using three selected models. Significant model to model as well as data to model differences wer e frequently observed. During summer, models tended to underpredict NO (-25 to -60%) while significantly overpredicting HNO3 (+ 250 to + 400%) especia lly in the upper troposphere. Similarly, the seasonal HNO3 variations predi cted by some models were opposite to those observed. PAN was generally over predicted, especially in the upper troposphere, while NOy was underpredicte d. Ozone on average was better simulated but significant deviations at spec ific locations were evident. By comparing model predictions with observatio ns, an overall quantitative assessment of the accuracy with which these thr ee models describe the global distribution of measured reactive nitrogen sp ecies is provided. No reliable trend information for any of the reactive ni trogen species was possible based on the presently available data set. The reactive nitrogen data currently offer only a limited spatial and temporal coverage for the validation of global models. (C) 1999 Elsevier Science Ltd . All rights reserved.