Isoprene Mixing Ratios Measured at Twenty Sites in China During 2012–2014: Comparison With Model Simulation. Issue 24 (16th December 2020)

• Record Type: Journal Article
• Authors: Zhang, Yanli; Zhang, Ruixiong; Yu, Jianzhen; Zhang, Zhou; Yang, Weiqiang; Zhang, Huina; Lyu, Sujun; Wang, Yuesi; Dai, Wei; Wang, Yuhang; Wang, Xinming
• Is Part Of: Journal of geophysical research. Volume 125:Issue 24(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-16
• Subjects: ambient observation -- China -- Isoprene -- model of emissions of gases and aerosols from nature -- model simulation -- regional chEmical trAnsport model; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD033523
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: 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 ∼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. Plain Language Summary: Isoprene alone accounts for approximately one‐third of global emission of volatile organic compounds from both nature and human activities, yet in many parts of the world biogenic isoprene emission estimates have large uncertainties (reported isoprene emission estimates span 4–29 TgC y −1 in China), and narrowing these uncertainties is a challenging task. Here we collected ambient air samples concurrently at 20 sites over China during 2012–2014, and made measurement‐model comparison to check the emission estimates for isoprene, and found that although overall observed and predicted average isoprene levels matched well particularly during growing seasons, there exists a south‐north discrepancy that model simulated averages in the south were much higher than the north while their observed averages were quite near each other. Modeled values overestimated at most southern sites but underestimated at most northern sites, probably the fast afforestation in the north and rapid urbanization in the southeast were inadequately characterized in the model. Abnormally higher isoprene levels were observed in winter at some northern sites probably due to contribution from nonbiogenic sources. Our results highlight that high‐resolution PFT/LAI, field campaigns with higher spatial and temporal resolutions, as well as biomass burning activity data, are necessary for better observation‐model comparison. Key Points: Ambient isoprene mixing ratios observed at 20 sites across China during 2012–2014 are compared with the MEGAN‐REAM model simulation The model simulated averages in the south were much higher than those in north, while the observed averages were much more similar Abnormally high isoprene levels were observed in winter at some northern sites probably due to contributions from nonbiogenic sources