亚热带城乡复合系统BVOC排放清单——以台州地区为例

挥发性有机复合物(VOC)对大气的化学组成有重要的影响。植物排放的VOC(BVOC)比人为源VOC(AVOC)具有更高的反应活性。通过实地调查台州地区的植被构成和分布,综合BVOC排放速率的测定值和文献数值、当地气象资料等,研究了台州城市和周边地区的BVOC排放强度、时空格局及种类特征。结果表明,2009年台州地区的BVOC年排放量为4.6×1010 g C,其中异戊二烯、单萜和其他VOC所占的比重分别为93.8%、3.5%和2.7%。野外森林中毛竹林排放强度(133.8 t C.km-.2a-1)高出马尾松林、杉木林和常绿阔叶林(分别为0.9、0.8、0.6 t C.km-.2a-1)2个数量级,因此从改善大气质量角度考虑应当抑制毛竹林的扩张。城市行道树及河道树的BVOC排放强度为2.4 t C.km-.2a-1,公园及居民区绿地为1.6 t C.km-.2a-1,均高于野外除毛竹林外的其他植被类型。台州市区的主要树种中,垂柳、合欢、龙爪槐和枫香的单株排放强度较高,而香樟、广玉兰、银杏等单株排放强度相对较低。可优先选择这些排放强度低的树种用作城市绿化。研究结果也可为处在相近气候带的城市中绿化树种的选择和大气质量的改善提供科学依据。

An inventory of BVOC emissions for a subtropical urban-rural complex: Greater Taizhou Area

VOCs (volatile organic compounds) are believed to have close relationships with the chemical composition and physical characteristics of the atmosphere. Biogenic VOCs (BVOCs) are more reactive than anthropogenic VOCs (AVOCs), can contribute to tropospheric ozone and secondary particle formation, and have indirect effects on climate change. Estimates of regional BVOC emissions are thus crucial input parameters of air quality models. However, most of the BVOC inventory work has concentrated on natural habitats in Europe, North America and some tropical regions. Although an increasing number of studies are being carried out in tropical and mid-latitude regions throughout Asia in recent years, few studies are concerned with humid subtropical areas, especially in urban areas. Here, a field survey of vegetation composition and distribution was conducted in a subtropical urban-rural complex, Greater Taizhou Area (28°01'-29°20'N,120°17'-121°56'E), Zhejiang Province. Different models were developed and used to estimate leaf biomass of the main tree species. BVOC were divided into isoprene, monoterpenes and other VOCs (OVOCs) and different algorithms were used calculate them separately. The isoprene emission rate data of the main tree species in this area was identified using a plant enclosure approach followed by a GC-PID analysis, while other emission data was compiled from measurements available in China. Tree distribution information, leaf biomass, plant emissions, and meteorological data were combined to investigate the BVOC emission intensity, temporal and spatial patterns and species features in Greater Taizhou Area. Results showed that the annual BVOC emissions of Taizhou in 2009 is 4.6×10¹⁰ g C. Isoprene, total monoterpenes and OVOCs emissions account for 93.8%, 3.5% and 2.7%, respectively. In rural area, the emission intensity of bamboo forest (133.8 t C·km^-2·a^-1) is two orders of magnitude higher than those of Pinus massoniana forest, Cunninghamia lanceolata forest and evergreen broad-leaved forests (0.9, 0.8, 0.6 t C·km^-2·a^-1, respectively). So from the perspective of improving air quality, expansion of bamboo forests should be inhibited while increasing the proportion of evergreen broad-leaf forests. Within Taizhou city, the BVOC emission intensity of street and riparian trees is 2.4 t C·km^-2·a^-1, while the emission intensity of trees in parks and residential areas is 1.6 t C·km^-2·a^-1, both of which are higher than that of any rural forest types other than bamboo forest. Among the primary tree species within the built-up area, Salix babylonica, Albizia julibrissin, Sophora japonica and Liquidambar formosana exhibited high BVOC emission potential, while Cinnamomum camphora, Magnolia grandiflora and Ginkgo biloba have relatively low emission potential. There were no significant differences in the emission patterns between native and nonnative tree species in Taizhou area. Species with low BVOC emission potential should therefore be chosen for future in urban greening initiatives. The annual BVOC emissions of Taizhou are much higher than those of Beijing (1.6×10¹⁰ g C/a) and Hong Kong (1.6×10¹⁰ g C/a) because these areas vary in climate and vegetation characteristics. This study also provides a scientific basis for the selection of tree species and improvement of air quality in cities in similar climate zones as Taizhou.