Abstract:
The variability and trend of ozone (O3) in the Upper troposphere and Lower Stratosphere (UTLS) over
the Asian region needs to be accurately quantifed. Ozone in the UTLS radiatively heats this region and
cools the upper parts of the stratosphere. This results in an impact on relative humidity, static stability
in the UTLS region and tropical tropopause temperature. A major challenge for understanding ozone
chemistry in the UTLS is sparse observations and thus the representation of precursor gases in model
emission inventories. Here, we evaluate ozonesonde measurements during August 2016 at Nainital,
in the Himalayas, against ozone from multiple reanalyses and the ECHAM6-HAMMOZ model. We
fnd that compared to measurements both reanalyses and ECHAM6-HAMMOZ control simulation
overestimate ozone mixing ratios in the troposphere (20 ppb) and in the UTLS (55 ppb). We performed
sensitivity simulations using the ECHAM6-HAMMOZ model for a 50% reduction in the emission of
(1) NOx and (2) VOCs. The model simulations with NOX reduction agree better with the ozonesonde
observations in the lower troposphere and in the UTLS. Thus, neither reanalyses nor ECHAM6 HAMMOZ results can reproduce observed O3 over the South Asian region. For a better representation
of O3 in the ECHAM6-HAMMOZ model, NOX emission should be reduced by 50% in the emission
inventory. A larger number of observations of ozone and precursor gases over the South Asian region
would improve the assessment of ozone chemistry in models.
