Detection in the summer polar stratosphere of air plume pollution from East Asia and North America by balloon-borne in situ CO measurements

Abstract

Abstract. The SPIRALE and SWIR balloon-borne instruments have been launched in the Arctic polar region (near Kiruna, Sweden, 67.9° N, 21.1° E) during summer on 7 and 24 August 2009 and on 14 August 2009, respectively. The SPIRALE instrument performed in situ measurements of several trace gases including CO and O3 between 9 and 34 km height, with very high vertical resolution (~5 m). The SWIR-balloon instrument measured total and partial column of several species including CO. The CO stratospheric profile from SPIRALE on 7 August 2009 shows some specific structures with strong abundance of CO in the low levels (potential temperatures between 320 and 380 K, i.e. 10–14 km height). These structures are not present in the CO vertical profile of SPIRALE on 24 August 2009, for which the volume mixing ratios are typical from polar latitudes (~30 ppb). CO total columns retrieved from the IASI-MetOp satellite sounder for the three dates of flights are used to understand this spatial and temporal CO variability. SPIRALE and SWIR CO partial columns between 9 and 34 km are compared, allowing us to confirm that the enhancement of CO is localised in the stratosphere. The measurements are investigated also in terms of CO:O3 correlations and with the help of several modelling approaches (trajectory calculations, potential vorticity fields, results of chemistry transport model), in order to characterize the origin of the air masses sampled. The emission sources are qualified in terms of source type (fires, urban pollution) using NH3 and CO measurements from IASI-MetOp and MODIS data on board the TERRA/AQUA satellite. The results give strong evidence that the unusual abundance of CO on 7 August is due to surface pollution plumes from East Asia and North America transported to the upper troposphere and then entering the lower stratosphere by isentropic advection. This study highlights that the composition of low polar stratosphere in summer can be affected by anthropogenic surface emissions through long range transport.