Estimation Of Biogenic VOCs Emissions In China Based On Remote Sensing Data

Volatile Organic Compounds (VOCs) are the general term of a series of hydrocarbons which widely exist in atmosphere, and they play an important role in process of some common air pollution, such as high concentrations of ozone, haze and photochemical smog. Biogenic VOCs (BVOCs) are especially essential for regional air quality and climate, because they are typically more reactive than anthropogenic VOCs (AVOCs) and have greater global emission. As a result, high-resolution, high time, high availability inventory of BVOCs emissions is significant for research and policy about regional air pollution and climate.In order to study emission features of BVOCs in China, the widely-used Model of Emissions of Gases and Aerosols from Nature (MEGAN) was adopted. Recent information on leaf area index (LAI) were based on the remote sensing data, and Up-to-date observations on emission factors were investigated from literature. It is assumed that January, April, July and October had the same pattern with winter, spring, summer and autumn, hourly BVOCs emissions of each grid in China in2010were calculated, with spatial grid resolution of10km. Spatial distribution and time changes of LAI were retrieved from2008～2010MODIS LAI database. MODIS LAI can tell the spatial distribution of vegetation growth, and show changes in a long period, which is a great advantage over the traditional ground surveys of gathering vegetation information. Lots of observations on emission factors from literature were collected, selected and processed to set up a reliable database for ISOP and MON, as while as Special Leaf Area (SLA).The results show that the annual amount BVOCs emissions in China was19.9×106t(C), with10.1×106t isoprene (ISOP), accounting for44.9%;5.5×106t monoterpene (MON),31.5%;4.3×106t other VOC (OVOC),23.6%. The southern of China emits more BOVCs than the northern part. High emission intensities above1500kg·km-2·a-1are usually found in forest along Xing’an Mountain, Changbai Mountain, Taihang-Luliang Mountain. Emission intensities are rather high near Tianshan in Xinjiang Province, while pretty low in southern Inner Mongolia, other parts of Xinjiang and Qinghai Province. BVOCs emission is strong in Qinling-Daba Mountain and south China, especially in Hainan Province and southwest forest areas, due to the high temperature, high precipitation and dense vegetation there. Total annual amount of BVOCs in Yunnan, Sichuan, Guangxi, Jiangxi, Inner Mongolia Province were relatively high, with Yunnan accounting for15%of total. Provinces of Yunnan, Fujian, Jiangxi, Guangxi and Guangdong show strong intensities of emissions than other part of China.Seasonal variations of BVOCs Emissions are very significant in China, and contributions of spring, summer, autumn and winter to the yearly total were14.8%、67.2%、14.3%and3.7%, respectively. Emission intensities are rather low in the north in winter, while they are relatively high all over China in summer, especially in northern mountain forest areas, southwest forest areas and south China. What’s more, BVOCs emissions show a diurnal variation. Plants stop emitting ISOP after sunset, and begin to emit at dawn. ISOP emissions reach peak at about13～14pm. MON and OVOC are released at night without solar radiation, and the intensities change as temperature changes. The lowest point shows at5-6am before dawn, and the peak at about15pm.We improved BVOCs inventory in China by retrieving LAI from remote sensing data and updating emission factors. The result may provide some reference for some research about regional air pollution and climate, and ozone control strategies. However, there are still high uncertainties due to inaccurate of emission factors, SLA, vegetation distribution database, remote sensing data, and model MEGAN itself, and those uncertainties will be focuses in future studies.