上海中心城区二氧化碳通量特征分析

利用位于上海中心城区徐家汇站的涡动相关湍流通量资料,对该区域2012年12月至2013年11月二氧化碳（CO₂）通量的时间变化、空间分布特征、年总排放量进行分析。结果表明：中心城区徐家汇为CO₂通量的源区,CO₂通量的日变化呈现与交通流量相对应的双峰现象,冬季的通量值普遍小于其他季节,尤其在早高峰时段更为明显。节假日CO₂通量的早高峰效应并不明显,其峰值明显低于工作日,且有滞后的趋势。各方向CO₂通量大小与其周边下垫面情况密切相关,夏季白天在商业建筑密集区和主要道路处,CO₂通量明显高于其他季节。上海中心城区CO₂通量的年总排放量为44.5 kg/（m²·a）,高于国内外其他城市的市中心或高密度住宅区的数值,这主要和观测时段相对偏晚、植被覆盖率偏低、周边高层建筑和主干道偏多有关。     

Effects of an Urban Park and Residential Area on the Atmospheric CO2 Concentration and Flux in Seoul, Korea

The CO₂ concentrations and fluxes over an urban forest site (Namsan) and an urban residential region (Boramae) in Seoul, Korea, during the non-growing season (2–4 March 2011), the growing season (10–12 June 2011), and the late-growing season (22–24 September 2011) were analyzed. The CO₂ concentrations of two sites showed nearly the same diurnal variation, with a maximum value occurring during the night and a minimum value occurring during daytime, as well as the same seasonal variation, with a maximum value during the non-growing season (early spring) and a minimum value during the growing season (summer). The CO₂ flux over the urban forest did not show any typical diurnal variation during the non-growing season, but did show diurnal variation with a small positive value during the night and a large negative value during daytime in the growing and late-growing seasons due to photosynthesis in the urban forest. The CO₂ flux over the urban residential region showed a positive daily mean value for all periods, with large values during the non-growing season and small values during the growing season, and it also showed diurnal variation with two maxima at 0600–1000 LST and 1800–2400 LST, and two minima at 0300-0600 LST and 1100-1500 LST, and was strongly correlated with the use of liquefied natural gas for cooking and heating by surrounding houses.     

Numerical simulations of pollutant dispersion in an idealized urban area,for different meteorological conditions

In order to estimate the impacts of buildings on air pollution dispersion, numerical simulations are performed over an idealized urban area, modelled as regular rows of large rectangular obstacles. The simulations are evaluated with the results of the Mock Urban Setting Test (MUST), which is a near full-scale experiment conducted in Utah’s West Desert area: it consists of releases of a neutral gas in a field of regularly spaced shipping containers. The numerical simulations are performed with the model Mercure_Saturne, which is a three-dimensional computational fluid dynamics code adapted to atmospheric flow and dispersion simulations. It resolves complex geometries and uses, in this study, a k–∈ closure for the turbulence model. Sensitivity studies focus on how to prescribe the inflow conditions for turbulent kinetic energy. Furthermore, different sets of coefficients available in the literature for the k–∈ closure model are tested. Twenty MUST trials with different meteorological conditions are simulated and detailed analyses are performed for both the dynamical variables and average concentration. Our results show overall good agreement according to statistical comparison parameters, with a fraction of predictions for average concentration within a factor of two of observations of 67.1%. The set of simulations offers several inflow wind directions and allows us to emphasize the impact of elongated buildings, which create a deflection of the plume centerline relative to the upstream wind direction.