电力减排对华东空气质量影响的数值模拟研究

我国经济正处在高速发展时期,电力需求将持续增长,但以燃煤为主的电力工业带来的能源消耗和环境污染问题也不容忽视。为了进一步了解电力排放对华东空气质量的影响,本文应用中尺度大气动力-化学耦合模式WRF-Chem针对两种不同的电厂减排情景模拟分析了冬季华东地区主要污染物浓度变化量和分布情况,得到以下结论：(1)模式能较好模拟华东主要大气污染物的时间变化规律和空间分布特征;(2)华东冬季主要大气污染物浓度高值区为山东西部、安徽北部及长三角地区,冬季大气环流条件不利近地面污染物扩散,易造成污染物堆积;(3) 减排的敏感性试验表明：电厂排放减半时华东大部地区SO2、NO2的浓度降低约10~30%,关闭时约30~50%;PM2.5和PM10在江西和福建沿海一带减少较多,电厂排放减半时约5%,关闭时约10%;CO基本不受电厂减排影响,仅降低1~2%;而O3在电厂排放减半或关闭时在华东大部地区增加30%以上。     

Characteristics of clouds,precipitation, and latent heat in midlatitude frontal system mixed with dust storm from GPM satellite observations and WRF simulations

A heavy dust storm originating in Mongolia and Inner Mongolia traveled to Northeast China and met a midlatitude frontal system on May 3, 2017. The potential ice nuclei (IN) effects of mineral dust aerosols on the vertical structure of clouds, precipitation, and latent heat (LH) were studied using Global Precipitation Mission (GPM) satellite observations and Weather Research and Forecasting (WRF) model simulations. The WRF simulations correctly captured the main features of the system, and the surface rain rate distribution was positively correlated with data retrieved from the GPM Microwave Imager. Moreover, the correlation coefficient increased from 0.31 to 0.54 with increasing moving average window size. The WRF-simulated rainfall vertical profiles are generally comparable to the GPM Dual-Frequency Precipitation Radar (DPR) observations, particularly in low layers. The joint probability distribution functions of the rain rate at different altitudes from the WRF simulation and GPM observations show high positive correlation coefficients of ~0.80, indicating that the assumptions regarding the raindrop size distribution in the WRF model and DPR retrieval were consistent. Atmospheric circulation analysis and aerosol optical depth observations from the Himawari-8 satellite indicated that the dust storm entered only a narrow strip of the northwest edge of the frontal precipitation system. The WRF simulations showed that in carefully selected areas of heavy dust, dust can enhance the heterogeneous ice nucleation process and increase the cloud ice, snowfall, high-altitude precipitation rate, and LH rate in the upper layers. This effect is significant at temperatures of ?15 °C to ?38 °C and requires dust number concentrations exceeding 106 m?3. It is important to accurately classify the dusty region in this type of case study. In the selected vertical cross section, the WRF-simulated and DPR-retrieved LH have comparable vertical shapes and amplitudes. Both results reflect the structure of the tilted frontal surface, with positive LH above it and negative LH below it. The simulated area-averaged LH profiles show positive heating in the entire column, which is a convective-dominated region, and this feature is not significantly affected by dust. DPR-based LH profiles show stratiform-dominated or convective-dominated shapes, depending on the DPR retrieval product.     

Analysis of the causes of heavy aerosol pollution in Beijing,China: A case study with the WRF-Chem model

The causes and variability of a heavy haze episode in the Beijing region was analyzed. During the episode, the PM_2.5 concentration reached a peak value of 450 μg/kg on January 18, 2013 and rapidly decreased to 100 μg/kg on January 19, 2013, characterizing a large variability in a very short period. This strong variability provides a good opportunity to study the causes of the haze formation. The in situ measurements (including surface meteorological data and vertical structures of the winds, temperature, humidity, and planetary boundary layer (PBL)) together with a chemical/dynamical regional model (WRF-Chem) were used for the analysis. In order to understand the rapid variability of the PM_2.5 concentration in the episode, the correlation between the measured meteorological data (including wind speed, PBL height, relative humidity, etc.) and the measured particle concentration (PM_2.5 concentration) was studied. In addition, two sensitive model experiments were performed to study the effect of individual contribution from local emissions and regional surrounding emissions to the heavy haze formation. The results suggest that there were two major meteorological factors in controlling the variability of the PM_2.5 concentration, namely, surface wind speed and PBL height. During high wind periods, the horizontal transport of aerosol particles played an important role, and the heavy haze was formed when the wind speeds were very weak (less than 1 m/s). Under weak wind conditions, the horizontal transport of aerosol particles was also weak, and the vertical mixing of aerosol particles played an important role. As a result, the PBL height was a major factor in controlling the variability of the PM_2.5 concentration. Under the shallow PBL height, aerosol particles were strongly confined near the surface, producing a high surface PM_2.5 concentration. The sensitivity model study suggests that the local emissions (emissions from the Beijing region only) were the major cause for the heavy haze events. With only local emissions, the calculated peak value of the PM_2.5 concentration was 350 μg/kg, which accounted for 78% of the measured peak value (450 μg/kg). In contrast, without the local emissions, the calculated peak value of the PM_2.5 concentration was only 100 μg/kg, which accounted for 22% of the measured peak value.     

北京冬奥会和冬残奥会历史同期气溶胶污染的高空环流特征研究

通过分析北京和张家口地区长期地面气象资料、气溶胶浓度数据和探空数据,研究冬奥会和冬残奥会历史同期(2015—2019年的2月1日至3月20日)的气象条件和气溶胶污染过程,并利用数值模拟和客观环流分型方法,探究高空环流和区域输送的影响。结果表明,北京和张家口两地的气溶胶污染过程与近地面的暖、湿和小风条件有关。在850hPa高度,当两地受西北风影响时,近地面的气溶胶浓度较低。北京的重污染过程主要与850hPa高度的西南风有关,张家口的重污染则主要与850hPa高度的西南风和南风有关。虽然北京与张家口两市中心相距160多公里,但两地的气溶胶污染和位温垂直结构变化有很强的关联性。当华东地区存在较强的高压系统时,来自京津冀以南地区850hPa高度的暖空气会输送到北京和张家口,使两地同时出现高空增温现象,进而增强对流层下部的热力稳定度,不利于边界层的发展和污染物的垂直扩散。此外,当上述环流出现时,河北南部、山西北部和内蒙古中部等地区排放的污染物会通过输送过程影响北京。张家口地区海拔较高,除本地排放外,影响其空气质量的污染气团主要来自西部的上游地区。因此,当出现不利的高空环流形势时,除需要控制本地的...     

基于WRF-Chem的AOD预报在一次沙尘天气中的研究

气溶胶光学厚度(AOD)是表征大气气溶胶光学特征的最基本量;它可以用来推算大气气溶胶含量,是确定大气气溶胶辐射气候效应及大气污染程度的关键因子。利用WRF-Chem数值模式对我国北方2010年3月19~23日的一次沙尘天气过程进行了模拟分析,主要分析了模式对于AOD的预报能力。结果表明:模式对于气溶胶光学特性具有较好的模拟能力,模拟结果中AOD、PM2.5、PM10的时空分布具有很好的一致性。通过与MODIS AOD卫星资料和地基AERONET观测网站点实测数据进行对比分析,发现AOD模拟结果与卫星产品和站点实测数据较吻合,模式24 h预报能够较好地体现AOD随时间的变化特征。