Abstract
Abstract. Balloon-borne measurements of ozone in Lhasa (29.66∘ N, 91.14∘ E; 3650 m above sea level) in August 2013 are investigated using backward trajectory calculations performed with the Chemical Lagrangian Model of the Stratosphere (CLaMS). Measurements show three time periods characterized by high ozone mixing ratios (OMRs) in the troposphere on 8, 11, and 18–20 August 2013 during the Asian summer monsoon (ASM) season. Here, we verified two different sources for the enhanced ozone values in the troposphere. First, transport of polluted air from the boundary layer, and second downward transport from the stratosphere by stratospheric intrusions. Air pollution from South Asia through convective and long-range transport plays a key role in enhancing middle tropospheric OMRs up to 90 % on 8 August and up to 125 % on 11 August 2013 compared to monthly mean ozone of August 2013. Stratospheric air intruded from the northern high-latitudes to the southeastern flank of the ASM anticyclone to the troposphere and is identified as the source of enhanced ozone according to backward trajectory calculation and satellite measurements by the Ozone Monitoring Instrument (OMI) and the Atmospheric Infrared Sounder (AIRS). Air parcels with high ozone moved from the high-latitude lower stratosphere to the middle and upper troposphere. These air parcels are then transported to Lhasa over long distances and enhanced upper and middle tropospheric ozone over Lhasa during 18–20 August 2013. Our findings demonstrate that the strong variability of ozone within the ASM anticyclone in the free troposphere is caused by transport from very different regions of the atmosphere.
Highlights
In the troposphere, ozone acts as an important greenhouse gas, which has a positive radiative forcing (0.4 ± 0.2 W m−2) through the direct or indirect greenhouse effect for the period 1750–2011
The high ozone value is marked by dark shading for the ozone mixing ratios (OMRs) relative changes above 30 %; in the following, we solely focus on these air masses
We focus on enhanced OMRs observed in the middle and upper troposphere over Lhasa on 8, 11, and 18–20 August 2013
Summary
Ozone acts as an important greenhouse gas, which has a positive radiative forcing (0.4 ± 0.2 W m−2) through the direct or indirect greenhouse effect for the period 1750–2011. Tropospheric tracers within the ASM anticyclone are separated from the anticyclone and are further transported globally This will affect the trace gas concentration in the UTLS resulting in significant changes in radiative forcing (Garny and Randel, 2016). Stratosphere-to-troposphere transport along the subtropical jet stream occurs over the Pacific Ocean This is an important process for increasing ozone in the middle and upper troposphere in the region of the ASM (Trickl et al, 2011). We combined in situ measurements with satellite data and trajectory calculations using the Chemical Lagrangian Model of the Stratosphere (CLaMS, McKenna et al, 2002; Pommrich et al, 2014) to analyse the origin of high ozone structures found in the middle and upper troposphere in Lhasa over the Tibetan Plateau in August 2013.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
