Comparison of ozone sonde measurements in the upper troposphere and lower Stratosphere at Nainital, India during StratoClim with renalysis and chemistry-climate model data

Abstract

AbstractThe variability and trend of ozone (O3) in the Upper troposphere and Lower Stratosphere (UTLS) over the Asian region needs to be accurately quantified. A major challenge for understanding ozone chemistry is sparse observations in the region 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 find 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 NOXreduction agree better with the ozonesonde observations in the lower troposphere and in the UTLS. Thus, neither reanalysis nor ECHAM6-HAMMOZ can reproduce observed O3over the South Asian region. For a better representation of O3in the ECHAM6-HAMMOZ model, NOXemission should be reduced by 50% in the emission inventory. A larger number of observations over the South Asian region would improve the assessment of ozone chemistry in models.