中国黄海西岸海陆风循环结构研究

陆海风是由于海陆表面之间的比热容不同而导致的昼夜热量分布差异,从而在海岸附近引发的大气中尺度循环系统.本文利用多普勒风激光雷达Windcube100s首次对黄海西海岸的海陆风的循环结构进行了观测研究.在2018年8月31日至9月28日观测期间发现,海陆风发展高度一般在700 m至1300 m.海陆风转化持续的时间为6小时至8小时.在425m高度,海风水平风速出现最大值,平均为5.6 m s^(-1).陆风最大水平风速出现在370 m,约为4.5 ms^(-1).最大风切变指数在1300m处,为2.84;在陆风向海风转换过程中,最大风切变指数在700m处,为1.28.在同一高度上,风切变指数在海风盛行和陆风盛行时的差值范围为0.2-3.6,风切变能反映出海陆风的发展高度.

Optical Properties and Source Analysis of Aerosols over a Desert Area in Dunhuang,Northwest China

Aerosol observational data for 2012 obtained from Dunhuang Station of CARE-China（Campaign on Atmospheric Aerosol Research Network of China） were analyzed to achieve in-depth knowledge of aerosol optical properties over Dunhuang region. The results showed that the annual average aerosol optical depth（AOD） at 500 nm was 0.32 ± 0.06, and the ？ngstr？m exponent（α） was 0.73 ± 0.27. Aerosol optical properties revealed significant seasonal characteristics. Frequent sandstorms in MAM（March–April–May） resulted in the seasonal maximum AOD, 0.41 ± 0.04, and a relatively smaller αvalue, 0.44 ± 0.04. The tourism seasons, JJA（June–July–August） and SON（September–October–November） coincide with serious emissions of small anthropogenic aerosols. While in DJF（December–January–February）, the composition of the atmosphere was a mixture of dust particles and polluted aerosols released by domestic heating; the average AOD and αwere 0.29 ± 0.02 and 0.66 ± 0.17, respectively. Different air masses exhibited different degrees of influence on the aerosol concentration over Dunhuang in different seasons. During MAM, ranges of AOD（0.11–1.18） and α（0.06–0.82） were the largest under the dust influence of northwest-short-distance air mass in the four trajectories. Urban aerosols transported by northwest-short-distance air mass accounted for a very large proportion in JJA and the mixed aerosols observed in SON were mainly conveyed by air masses from the west. In DJF, the similar ranges of AOD and α under the three air mass demonstrated the analogous diffusion effects on regional pollutants over Dunhuang.

Transport Patterns and Potential Sources of Atmospheric Pollution during the ⅩⅩⅣ Olympic Winter Games Period

The attainment of suitable ambient air quality standards is a matter of great concern for successfully hosting the ⅩⅩⅣ Olympic Winter Games(OWG). Transport patterns and potential sources of pollutants in Zhangjiakou(ZJK) were investigated using pollutant monitoring datasets and a dispersion model. The PM_(2.5) concentration during February in ZJK has increased slightly(28%) from 2018 to 2021, mostly owing to the shift of main potential source regions of west-central Inner Mongolia and Mongolian areas(2015–18) to the North China Plain and northern Shanxi Province(NCPS) after 2018.Using CO as an indicator, the relative contributions of the different regions to the receptor site(ZJK) were evaluated based on the source-receptor-relationship method(SRR) and an emission inventory. We found that the relative contribution of pollutants from NCPS increased from 33% to 68% during 2019–21. Central Inner Mongolia(CIM) also has an important impact on ZJK under unfavorable weather conditions. This study demonstrated that the effect of pollution control measures in the NCPS and CIM should be strengthened to ensure that the air quality meets the standard during the ⅩⅩⅣ OWG.

Optical,Radiative and Chemical Characteristics of Aerosol in Changsha City,Central China

Industrial pollution has a significant effect on aerosol properties in Changsha City,a typical city of central China.Therefore,year-round measurements of aerosol optical,radiative and chemical properties from 2012 to 2014 at an urban site in Changsha were analyzed.During the observation period,the energy structure was continuously optimized,which was characterized by the reduction of coal combustion.The aerosol properties have obvious seasonal variations.The seasonal average aerosol optical depth(AOD)at 500 nm ranged from 0.49 to 1.00,single scattering albedo(SSA)ranged from 0.93 to 0.97,and aerosol radiative forcing at the top of the atmosphere(TOA)ranged from−24.0 to 3.8 W m^−2.The chemical components also showed seasonal variations.Meanwhile,the scattering aerosol,such as organic carbon,SO42−,NO3−,and NH4+showed a decrease,and elemental carbon increased.Compared with observation in winter 2012,AOD and TOA decreased by 0.14 and−1.49 W m^−2 in winter 2014.The scattering components,SO42−,NO3−and NH4+,decreased by 12.8μg m^−3(56.8%),9.2μg m^−3(48.8%)and 6.4μg m^−3(45.2%),respectively.The atmospheric visibility and pollution diffusion conditions improved.The extinction and radiative forcing of aerosol were significantly controlled by the scattering aerosol.The results indicate that Changsha is an industrial city with strong scattering aerosol.The energy structure optimization had a marked effect on controlling pollution,especially in winter(strong scattering aerosol).

Validation of MODIS C6 AOD Products Retrieved by the Dark Target Method in the Beijing–Tianjin–Hebei Urban Agglomeration,China

The quality of the MODIS C6 3-km and 10-km aerosol optical depth（AOD） products retrieved by the Dark Target（DT）method is discussed using ground-based observations in the Beijing–Tianjin–Hebei region from 1 August 2007 to 31 July2008. Good consistency exists between the 3-km and 10-km products and ground-based observations. The retrieval accuracy of the two products both show distinctive seasonality. The percentage falling within the expected error（EE） is largest in the winter, moderate in the spring and autumn, and smallest in the summer. A worse overestimation appears in the spring and summer（27%–66%）. However, the 3-km and 10-km products over different surfaces still exhibit obvious deviations. The 10-km product performs better in the large cities, while the 3-km product has advantages in the suburbs. In urban areas, the percentage falling within EE of the 3-km AOD product（18%–59%） is lower than that for the 10-km AOD product（31%–69%）. However, in suburban areas, the percentage falling within EE of the 3-km AOD product（61%–84%） is higher than for the 10 km AOD product（54%–83%）.The percentages falling within EE differ considerably when the AOD is greater than1.5（73% and 63% for the 3-km and 10-km products, respectively）. On the whole, the 3-km（10-km） AOD product performs better in suburban（urban） areas.

2014-2017年华北平原PM_(2.5)组分消光与能见度对比研究

华北平原大气污染与低能见度状况一直是人们关切的问题.本文通过分析2014-2017年PM_(2.5)化学成分的浓度和消光效果,研究了华北平原典型城市保定市的大气污染特征.结果表明,PM_(2.5)分的年均浓度显示下降趋势,水溶性无机离子,碳质气溶胶和金属元素分别减少了11μgm^(-3),23μg m^(-3)和1796 ngm^(-3).NH_(4)^(+),NO_(3)^(-)和SO_4^(2-)是PM_(2.5)污染的主要污染物,三者之和占总离子浓度的82.9%.基于IMPROVE方程对细颗粒物进行重构,在观测期间PM_(2.5)质量浓度平均为93±69μgm^(-1),春季,夏季,秋季和冬季的消光系数分别为373.8±233.6 Mm^(-1)±,405.3±300.1 Mm^(-1),554.3±378.2 Mm^(-1)和1005.2±750.3 Mm^(-1).硫酸铵,硝酸铵和有机物对消光的贡献最大,不同季节下占比达55%~77%.通过PM_(2.5)组分进行重构,利用IMPROVE算法计算得到Rb_(sca),用能见度测量值转换得到Vb_(sca),二者具有较高的相关性(r^(2)=0.84);但存在Vb_(sca)的高值被低估,Vb_(sca)的低值被高估的现象;特别是当Rb_(sca)>1123 Mm^(-1)(对应能见度约小于2.0 km)时,Vb_(sca)的值被低估了17.6%.高浓度PM_(2.5)和高湿度对IMPROVE算法结果有显著的影响.

Refractory black carbon aerosols in rainwater in the summer of 2019 in Beijing:Mass concentration,size distribution and wet scavenging ratio

Black carbon(BC)aerosols in the atmosphere play a significant role in climate systems due to their strong ability to absorb solar radiation.The lifetime of BC depends on atmospheric transport,aging and consequently on wet scavenging processes(in-cloud and below-cloud scavenging).In this study,sequential rainwater samples in eight rainfall events collected in 2 mm interval were measured by a tandem system including a single particle soot photometer(SP2)and a nebulizer.The results showed that the volume-weighted average(VWA)mass concentrations of refractory black carbon(rBC)in each rainfall event varied,ranging from 10.8 to 78.9μg/L.The highest rBC concentrations in the rainwater samples typically occurred in the first fraction from individual rainfall events.The geometric mean median mass-equivalent diameter(MMD)decreased under precipitation,indicating that rBC with larger sizes was relatively aged and preferentially removed by wet scavenging.A positive correlation(R2=0.73)between the VWA mass concentrations of rBC in rainwater and that in ambient air suggested the important contribution of scavenging process.Additionally,the contributions of in-cloud and below-cloud scavenging were distinguished and accounted for 74%and 26%to wet scavenging,respectively.The scavenging ratio of rBC particles was estimated to be 0.06 on average.This study provides helpful information for better understanding the mechanism of rBC wet scavenging and reducing the uncertainty of numerical simulations of the climate effects of rBC.

影响我国霾天气的多尺度过程

频发的霾天气是我国现阶段面临的最主要大气环境问题之一.霾期间高浓度大气细颗粒物(PM2.5)是多种物理化学过程综合影响的结果,包括排放、气-粒转化、大气边界层、局地环流、天气与气候等过程.上述过程的时空尺度跨越了几个数量级,在空间尺度上涵盖了纳米尺度至上千千米尺度.多尺度过程本身的复杂性以及不同过程之间的相互影响是目前大气环境领域面临的最严峻挑战,直接影响到对于霾天气形成机制的科学认识、预报技术与数值模式研发,以及相应的大气污染治理.文章综述了在影响我国霾天气的多尺度过程及其与气溶胶的相互作用领域取得的研究进展.研究表明:二次气溶胶已经成为我国大气气溶胶的主要部分,在霾过程后期,液相非均相过程对气-粒转化有重要贡献;PM2.5呈现多时间尺度周期性振荡,包括1,4~7以及40~60 d等,边界层、天气和气候等多尺度过程是造成上述周期性变化的主因;已有证据表明,我国高气溶胶已经影响到该区域大气光化学、大气边界层,甚至天气和气候过程.气溶胶与上述过程的相互作用进一步影响了气溶胶浓度及其空间分布,但是此问题极为复杂,尚存在很大不确定性.为此,今后需重点加强以下研究:加强包含气溶胶理化性质、大气光化学、气象要素在内的多要素协同观测,重点开展对流层内多要素协同垂直探测;增强跨学科领域研究,尤其是大气物理-大气化学-天气/气候等多学科间的交叉性研究;加强气溶胶与大气化学、边界层、天气气候等过程相互作用的数值模拟研究.

Simulating Aerosol Size Distribution and Mass Concentration with Simultaneous Nucleation,Condensation/Coagulation, and Deposition with the GRAPES–CUACE

A coupled aerosol–cloud model is essential for investigating the formation of haze and fog and the interaction of aerosols with clouds and precipitation. One of the key tasks of such a model is to produce correct mass and number size distributions of aerosols. In this paper, a parameterization scheme for aerosol size distribution in initial emission,which took into account the measured mass and number size distributions of aerosols, was developed in the GRAPES–CUACE [Global/Regional Assimilation and Pr Ediction System–China Meteorological Administration（CMA） Unified Atmospheric Chemistry Environment model]—an online chemical weather forecast system that contains microphysical processes and emission, transport, and chemical conversion of sectional multi-component aerosols. In addition, the competitive mechanism between nucleation and condensation for secondary aerosol formation was improved, and the dry deposition was also modified to be in consistent with the real depositing length. Based on the above improvements, the GRAPES–CUACE simulations were verified against observational data during 1–31 January 2013, when a series of heavy regional haze–fog events occurred in eastern China. The results show that the aerosol number size distribution from the improved experiment was much closer to the observation, whereas in the old experiment the number concentration was higher in the nucleation mode and lower in the accumulation mode. Meanwhile, the errors in aerosol number size distribution as diagnosed by its sectional mass size distribution were also reduced. Moreover, simulations of organic carbon, sulfate, and other aerosol components were improved and the overestimation as well as underestimation of PM2.5 concentration in eastern China was significantly reduced,leading to increased correlation coefficient between simulated and observed PM2.5 by more than 70%. In the remote areas where bad simulation results were produced previously, the correlation coefficient grew from 0.35 to 0.61, and the mean mass concentration went up from 43% to 87.5% of the observed value. Thus, the simulation of particulate matters in these areas has been improved considerably.