Abstract
Abstract. Satellite observations reveal that China has been leading the global greening trend in the past 2 decades. We assessed the impact of land cover change as well as climate variability on total biogenic volatile organic compound (BVOC) emission in China from 2001–2016. We found the greening trend in China is leading a national-scale increase in BVOC emission. The BVOC emission level in 2016 could be 11.7 % higher than that in 2001 because of higher tree cover fraction and vegetation biomass. On the regional scale, the BVOC emission level from 2013–2016 could be 8.6 %–19.3 % higher than that from 2001–2004 in hotspots including (1) northeastern China, (2) Beijing and its surrounding areas, (3) the Qin Mountains, (4) Yunnan Province, (5) Guangxi–Guangdong provinces, and (6) Hainan island because of the land cover change without considering the impact of climate variability. The comparison among different scenarios showed that vegetation changes resulting from land cover management are the main driver of BVOC emission change in China. Climate variability contributed significantly to interannual variations but not much to the changing trend during the study period. In the standard scenario, which considers both land cover change and climate variability, a statistically significant increasing trend can still be found in regions including Beijing and its surroundings, Yunnan Province, and Hainan island, and BVOC emission total amount in these regions from 2013–2016 is 11.0 %–17.2 % higher that from 2001–2004. We compared the long-term HCHO vertical columns (VC) from the satellite-based Ozone Monitoring Instrument (OMI) with the estimation of isoprene emission in summer. The results showed statistically significant positive correlation coefficients over the regions with high vegetation cover fractions. In addition, the isoprene emission and HCHO VC both showed statistically significant increasing trends in the south of China where these two variables have high positive correlation coefficients. This result may support our estimation of the variability and trends of BVOC emission in this region; however, the comparison still has large uncertainties since the chemical and physical processes, including transportation, diffusion and chemical reactions, were not considered. Our results suggest that the continued increase in BVOC will enhance the importance of considering BVOC when making policies for controlling ozone pollution in China along with ongoing efforts to increase the forest cover fraction.
Highlights
Biogenic volatile organic compounds (BVOCs) play an important role in air quality and the climate system due to their large emission amount and reactivity (Guenther et al, 1995, 2006)
There is no significant trend of BVOC emission for S3 or S4, with fixed land cover and annually updated meteorological conditions, which demonstrates that meteorology was not the direct driver of the BVOC emission trend in China during this period
The estimated total BVOC emission in S5 has a statistically significant increasing trend of 0.26 % yr−1 (p
Summary
Biogenic volatile organic compounds (BVOCs) play an important role in air quality and the climate system due to their large emission amount and reactivity (Guenther et al, 1995, 2006). A recent study by Chen et al (2018) concluded that the global isoprene emission decreased by 1.5 % because of the tree cover change from 2000–2015, but in China, the isoprene emitted by broadleaf trees and nontrees increased by 3.6 % and 5.4 %, respectively. These studies have limitations in representing annual changes of vegetation; e.g., Li and Xie (2014) used fixed leaf area index (LAI) input of the year 2003 over the whole study period of 1981–2003. We used the long-term OMI 2005– 2016 record to evaluate the interannual isoprene variability we estimated in China
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