Isoprene Mixing Ratios Measured At Twenty Sites In China During 2012-2014: Comparison With Model Simulation

Measurement-model comparisons for various atmospheric species have been widely used for evaluating the reliability of model simulations, yet such comparisons are quite limited for atmospheric isoprene due to the lack of systematic observations over a large scale. Here, we collected ambient air samples concurrently at 20 sites in China during 2012-2014 and compared the observed isoprene mixing ratios with those simulated by coupling MEGAN v2.1 with the 3-D Regional chEmical trAnsport Model. The observed average isoprene concentration for all 1,731 samples is 0.35 +/- 0.03 ppbv, 13% higher than the model simulated average of 0.31 +/- 0.02 ppbv; while during the growing season, the simulated average (0.53 +/- 0.05 ppbv) is almost the same as the observed average (0.52 +/- 0.04 ppbv). The observed isoprene average level in the north (0.35 ppbv) is similar to that in the south (0.37 ppbv). However, the model simulated average in the south (0.53 ppbv) is similar to 4 times that in the north (0.14 ppbv). The model overestimated the observations at most southern sites but underestimated at most northern sites in the growing season, which might be resulted from inadequate characterization of isoprene-emitting land vegetation with fast afforestation in the north and rapid urbanization in the south. Compared to the model simulation, the observations revealed abnormally high isoprene levels in winter at some northern sites, largely due to nonbiogenic emissions, as evidenced by the enhancements of measured combustion tracers concurrent with the abnormally elevated isoprene levels.