北京森林BVOCs排放现状及动态变化特征分析

以北京地区森林植被为研究对象,基于森林资源清查蓄积资料和逐小时气象数据,采用光温影响模型对2000~2020年北京森林BVOCs排放量进行估算,并分析其对空气质量的影响.结果显示,2020年北京森林BVOCs排放量为39.57×10⁹g C,异戊二烯、单萜烯和OVOCs分别占72.19%、17.48%和10.32%,杨树、栎树等阔叶树是主要的异戊二烯排放源,油松等针叶树是主要的单萜烯排放源.2000~2020年森林BVOCs排放量从20.30×10⁹g C/a增加到39.57×10⁹g C/a,年平均增长率4.75%;BVOCs排放量的变化表现出明显阶段性特征,2000~2010年增长缓慢,2010~2020年出现大幅上升.20年间异戊二烯所占比重呈下降趋势,单萜烯和OVOCs所占比重则呈上升趋势;杨树对BVOCs排放量的贡献逐渐降低,栎树和其他阔叶树的贡献明显增加,北京新增森林更加注重物种多样化.2000~2020年,BVOCs的O₃生成潜势从181.76×10⁹g增加到331.07×10⁹g,异戊二烯占92.70%,是主要的贡献者;SOA生成潜势从1.11×10⁹g增加到2.65×10⁹g,单萜烯和异戊二烯分别占75.40%和24.60%.O₃生成潜势最大的树种是杨树,SOA生成潜势最大的树种是油松.森林BVOCs排放在夏季对O₃污染的贡献最大,未来绿化中应考虑优化树种组成.

The current status and characteristics of variations in forest BVOCs emissions in Beijing

Accurate estimation of biogenic volatile organic compounds (BVOCs) emissions is necessary for developing effective air pollution control measures. To understand the current status and characteristics of variations in forest BVOCs emissions in Beijing, historical BVOCs emission inventories for the period from 2000 to 2020 were developed based on the volume data of forest resources survey, hourly meteorological data and light-temperature model. The results show that the forest BVOCs emissions in 2020 were 39.57×10⁹g C, of which isoprene, monoterpene and other VOCs accounted for 72.19%, 17.48% and 10.32%, respectively. Broadleaf trees emitted the largest amount of isoprene and total BVOC emissions, while conifers made the largest monoterpene emission. Results show that Beijing’s annual forest BVOCs emissions had increased from 20.30×10⁹g C in 2000 to 39.57×10⁹g Cin 2020, with an annual average increase rate of 4.75%. Isoprene, monoterpene and other VOCs accounted for 64.54%, 22.28% and 13.16% of the total increment, respectively. In the past 20 years, the proportion of isoprene decreased, while the proportion of monoterpene and OVOCs increased. The contribution to the BVOCs emissions tended to decrease for poplar while to increase significantly for quercus and other broadleaf trees, indicating that the new afforestation in Beijing has led to a higher species diversity. From 2000 to 2020, the ozone formation potential of BVOCs had increased from 181.76×10⁹ to 331.07×10⁹g C, of which isoprene was the main contributor, accounting for 92.70%. The secondary organic aerosol formation potential of BVOCs had increased from 1.11×10⁹ to 2.65×10⁹g C, and the contribution of monoterpene and isoprene was 75.40% and 24.60%, respectively. Poplar exhibits the highest ozone formation potential, and Pinus tabulaetormis shows the highest secondary organic aerosol formation potential. The forest BVOCs emissions made relatively higher contribution to ozone pollution in summer. Therefore, tree species optimization should be considered to mitigate BVOCs emissions.