| The worldwide urban population gets explored along with the acceleration of urbanization nowadays, percentage of urban residents increased from 10% in 1900 up to more than 50%, which will continue to increase in the next 50 years. Urban population in China increased from year to year since Reform and Opening up, it is forecasted that till 2020 half of the population will be settled in urban. Human health and well-beings are directly affected by urbanization, environmental issues caused by urbanization are drawing more attention than ever before from the Government as well as the general publics. VOCs (volatile organic compounds) were believed to have close relationships with the increment of ozone concentration in the atmosphere and haze days in urban. In the presence of sunlight and sufficient oxides of nitrogen, for example in polluted air, BVOCs can lead to the formation of O3, and it is believed that the increased haze days are having closely relationships with BVOC emissions. VOCs from anthropogenic sources (AVOCs) have been well studied, however, still little is known about VOC emissions from biogenic sources. BVOCs (biogenic VOCs) emitted from vegetation were estimated more than two times that emitted from anthropogenic sources. Here, we conduct the field survey of tree distribution and quantitation in Hangzhou and Taizhou, combined the mean BVOC emission rates of the local vegetation with meteorological data, estimate the BVOC emissions of the two urban-rural complex systems.The annual BVOC emission within the Hangzhou area is approximately 7.9x1010 g C, for which isoprene, monoterpenes, and other VOCs (OVOC) emissions account for 85%,8%, and 7%, respectively. Rural forests are the primary source of BVOC emissions in the region (99% accountability), of which bamboo forest (1.08×102 g C tree﹣1 yr﹣1) is the main contributor of isoprene emissions in Hanghzou. Within the rural area Cyclobalanopsis glauca, a native dominate species of humid subtropical evergreen broad-leaved forest regions, exhibited high emission potential (1.1 x 102 g C tree﹣1 yr﹣1) . Pinus massoniana, a native coniferous species, exhibited a relatively small emission potential of 38 g C tree﹣1 yr﹣1 , while Cunninghamia lanceolata, another native coniferous species, exhibited considerably lower potential (2.2 g C tree﹣1 yr﹣1 compared to the primary tree species found within the rural area. While in the city of Hangzhou, 70% of BVOC emissions derived from trees located in parkland and residential areas, and 30% derived from street trees. Among the primary species within Hangzhou, Salix babylonica exhibited the highest BVOC emission potential (2.7×103 g C tree﹣1 yr﹣1 followed by Liquidambar formosana (1.4×103 g C tree﹣1 yr﹣1and Albizzia jutibrissin (1.02x103gCtree﹣1 yr﹣1 .Annual BVOC emissions of Taizhou area is about 6.6×1010gCyr﹣1. Isoprene, total monoterpenes and OVOCs emissions account for 93%,4% and 3%, respectively. Forests are the main sources of BVOCs emission, of which bamboo forest contribute large amount of isoprene, while BVOC emissions within Taizhou city make a great contribution to the air pollution. And area average BVOC emissions of both the greespace types within Taizhou city are higher than that of the forest types (except bamboo forest). Within Taizhou city,68% of BVOC emissions derived from street trees and riparian trees,32% from parks and residential areas. Among the primary species of Taizhou, S. babylonica exhibited the highest BVOC emission potential, followed by A. jutibrissin (2.5x1O3g Ctree﹣1 yr﹣1 . Sophora japonica as the main ornamental tree species in Taizhou, has the BOVC emission potential slightly higher than L. formosana. The other two commonly seen tree species are P. elliottii and G. biloba, which exhibit the BVOC emission potentials as 8.1 g C tree﹣1 yr﹣1 and 4.6 g C tree﹣1 yr﹣1 , respectively.Both high and low emission species indicate that nonnative tree species showed no distinguishing emission patterns within the two areas. Among the four tree species possessing the highest emission potential in Hangzhou were the local tree species S. babylonica and L. formosana, which ranked as the top two, followed by the nonnative ornamental tree A. jutibrissin, the favored street tree species P. acerifolia, and the widely planted garden tree species P. elliottii. Moreover, the two nonnative tree species M. grandiflora and P. hindsii exhibited emission potentials between that of P. pubescens and Koelreuteria paniculata, the dominant native species of the rural bamboo forest and street trees within the Hangzhou area, respectively. The same situation exhibit in Taizhou area, where S. babylonica, S. japonica and P. elliottii are commonly seen native tree species which process the relatively high emission potentials, while the ornamental tree species A. jutibrissin have emission potential secondly only to S. babylonica. The other two nonnative tree species M. grandijlora and P. hindsii have similar emission rates with C. camphora and G. biloba.The annual area average BVOC emissions in GHA are 4.7 t C km﹣2 yr﹣1 , lower than that of Taizhou which is in the middle subtropical area (6.8 t C km﹣2 yr﹣1 . And the emission intensity of above two complex systems are lower than Hong Kong (7.8 t C km﹣2 yr﹣1 , which is located in the south of subtropical area. The emission intensities showed increasing as the latitude move south, which is closely related to the typical warm and humid climate and high diversity of vegetation of subtropical area.
|
PDF Full Text Request