Analysis of ozone and nitric acid in spring and summer Arctic pollution using aircraft, ground-based, satellite observations and MOZART-4 model: source attribution and partitioning

摘要

In this paper, we analyze tropospheric O together with HNOduring the POLARCAT (Polar Study using Aircraft, Remote Sensing, SurfaceMeasurements and Models, of Climate, Chemistry, Aerosols, and Transport)program, combining observations and model results. Aircraft observationsfrom the NASA ARCTAS (Arctic Research of the Composition of the Tropospherefrom Aircraft and Satellites) and NOAA ARCPAC (Aerosol, Radiation and CloudProcesses affecting Arctic Climate) campaigns during spring and summer of2008 are used together with the Model for Ozone and Related ChemicalTracers, version 4 (MOZART-4) to assist in the interpretation of theobservations in terms of the source attribution and transport of O andHNO into the Arctic (north of 60° N). The MOZART-4 simulationsreproduce the aircraft observations generally well (within 15%), but somediscrepancies in the model are identified and discussed. The observedcorrelation of O with HNO is exploited to evaluate the MOZART-4model performance for different air mass types (fresh plumes, freetroposphere and stratospheric-contaminated air masses).Based on model simulations of O and HNO tagged by source typeand region, we find that the anthropogenic pollution from the NorthernHemisphere is the dominant source of O and HNO in the Arctic atpressures greater than 400 hPa, and that the stratospheric influence is theprincipal contribution at pressures less 400 hPa. During the summer, intenseRussian fire emissions contribute some amount to the tropospheric columns ofboth gases over the American sector of the Arctic. North American fireemissions (California and Canada) also show an important impact ontropospheric ozone in the Arctic boundary layer.Additional analysis of tropospheric O measurements from ground-basedFTIR and from the IASI satellite sounder made at the Eureka (Canada) andThule (Greenland) polar sites during POLARCAT has been performed using thetagged contributions. It demonstrates the capability of these instrumentsfor observing pollution at northern high latitudes. Differences betweencontributions from the sources to the tropospheric columns as measured byFTIR and IASI are discussed in terms of vertical sensitivity associated withthese instruments. The first analysis of O tropospheric columnsobserved by the IASI satellite instrument over the Arctic is also provided.Despite its limited vertical sensitivity in the lowermost atmosphericlayers, we demonstrate that IASI is capable of detecting low-altitudepollution transported into the Arctic with some limitations.