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We analyze temporal trends of peroxyacetyl nitrate (PAN) retrievals from theMichelson Interferometer for Passive Atmospheric Sounding (MIPAS) during2002–2011 in the altitude range 8–23 km over the Asian summer monsoon(ASM) region. The greatest enhancements of PAN mixing ratios in the uppertroposphere and lower stratosphere (UTLS) are seen during the summer monsoonseason from June to September. During the monsoon season, the mole fractionsof PAN show statistically significant (at 2σ) positive trends from0.2 ± 0.05 to 4.6 ± 3.1 ppt yr−1 (except between12 and 14 km) which is higher than the annual mean trends of 0.1 ± 0.05 to2.7 ± 0.8 ppt yr−1. These rising concentrations point toincreasing NOx (= NO + NO2) and volatile organic compound(VOC) emissions from developing nations in Asia, notably India and China. We analyze the influence of monsoon convection on the distribution of PAN inUTLS with simulations using the global chemistry–climate modelECHAM5-HAMMOZ. During the monsoon, transport into the UTLS over the Asianregion primarily occurs from two convective zones, one the South China Seaand the other over the southern flank of the Himalayas. India and China host NOx-limited regimes for ozone photochemicalproduction, and thus we use the model to evaluate the contributions fromenhanced NOx emissions to the changes in PAN, HNO3 and O3concentrations in the UTLS. From a set of sensitivity experiments withemission changes in particular regions, it can be concluded that Chineseemissions have a greater impact on the concentrations of these species thanIndian emissions. According to SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) NO2 retrievals NOxemissions increases over India have been about half of those over Chinabetween 2002 and 2011

atmospheric chemistry and physics

Trends in peroxyacetyl nitrate (PAN) in the upper troposphere and lower stratosphere over southern Asia during the summer monsoon season: regional impacts