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Several hundred new measurements of the surface resistance to ozone uptake of grass, soil, sand, fresh water, sea water and snow are presented. Grass and soil show, in agreement with previous work, a daytime surface resistance of median value 100 s ml . The first direct evidence is presented of a nocturnal increase in surface resistance for grass and soil, with night-time values of surface resistance of about 300sm-'. The surface resistances of sea water and snow are considerably larger, about loo0 to 2000sml . A representative global ozone destruction rate for the earth's surface is derived using the above information and other published ozone data. Allowance is made for the latitudinal variation of the different types of surface, their various ozone destruction constants, the latitudinal and diurnal variation of ozone in the surface air and the diurnal variation of eddy transfer near the earth's surface. The global average ozone destruction rate is estimated to be in the range 2 to 6 x loz9 molecules s-l (0.5 to 1.5 x 1Ol2 kgyr-I). This range extends to slightly higher values than previous estimates. The ratio of ozone destruction rate between the southern and northern hemispheres is about 2: 3. The implications for the tropospheric ozone cycle are discussed.Species Differences in Rates of Vegetal Ozone Absorption, 45-62. 321-334. 94, 563-575. 62, 221-228. 6884. Arch. Met. Geophys. Biokl., Ser. A, 23, 131-135. J . R. Met. SOC., 98, 124134. Env. Poll., 3, 303-312.

Droughts have become more severe and recurrent over the Indian sub-continent during the second half of the twentieth century, leading to more severe hydro-climatic and socio-economic impacts over one of the most densely populated parts of the world. So far, droughts have mostly been connected to circulation changes concomitant with the abnormal warming over the Pacific Ocean, prevalently known as “El Niño”. Here, exploiting observational data sets and a series of dedicated sensitivity experiments, we show that the severity of droughts during El Niño is amplified (17%) by changes in aerosols. The model experiments simulate the transport of boundary layer aerosols from South Asian countries to higher altitudes (12–18 km) where they form the Asian Tropopause Aerosol Layer (ATAL) (~ 60–120°E, 20–40°N). During El Niño, the anomalous overturning circulation from the East Asian region further enriches the thickness of aerosol layers in the ATAL over the northern part of South Asia. The anomalous aerosol loading in the ATAL reduces insolation over the monsoon region, thereby exacerbating the severity of drought by further weakening the monsoon circulation. Future increases in industrial emissions from both East and South Asia will lead to a wider and thicker elevated aerosol layer in the upper troposphere, potentially amplifying the severity of droughts.

Abstract. The highly vibrant Asian summer monsoon (ASM) anticyclone plays an important role in efficient transport of Asian tropospheric air masses to the extratropical upper troposphere and lower stratosphere (UTLS). In this paper, we demonstrate long-range transport of Asian trace gases via eddy-shedding events using MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) satellite observations, ERA-Interim reanalysis data and the ECHAM5-HAMMOZ global chemistry-climate model. Model simulations and observations consistently show that Asian boundary layer trace gases are lifted to UTLS altitudes in the monsoon anticyclone and are further transported horizontally eastward and westward by eddies detached from the anticyclone. We present an event of eddy shedding during 1-8 July 2003 and discuss a 1995-2016 climatology of eddy-shedding events. Our analysis indicates that eddies detached from the anticyclone contribute to the transport of Asian trace gases away from the Asian region to the western Pacific (20-30 • N, 120-150 • E) and western Africa (20-30 • N, 0-30 • E). Over the last two decades, the estimated frequency of occurrence of eddy-shedding events is ∼ 68 % towards western Africa and ∼ 25 % towards the western Pacific.Model sensitivity experiments considering a 10 % reduction in Asian emissions of non-methane volatile organic compounds (NMVOCs) and nitrogen oxides (NO x ) were performed with ECHAM5-HAMMOZ to understand the impact of Asian emissions on the UTLS. The model simulations show that transport of Asian emissions due to eddy shedding significantly affects the chemical composition of the upper troposphere (∼ 100-400 hPa) and lower stratosphere (∼ 100-80 hPa) over western Africa and the western Pacific. The 10 % reduction of NMVOCs and NO x Asian emissions leads to decreases in peroxyacetyl nitrate (PAN) (2 %-10 % near 200-80 hPa), ozone (1 %-4.5 % near ∼ 150 hPa) and ozone heating rates (0.001-0.004 K day −1 near 300-150 hPa) in the upper troposphere over western Africa and the western Pacific.