How aerosol direct effects influence the source contributions to PM2.5 concentrations over Southern Hebei, China in severe winter haze episodes

Beijing-Tianjin-Hebei area is the most air polluted region in China and the three neighborhood southern Hebei cities, Shijiazhuang, Xingtai, and Handan, are listed in the top ten polluted cities with severe PM2.5 pollution. The objective of this paper is to evaluate the impacts of aerosol direct effects on air aualitv over the southern Hebei cities, as well as the im0acts when considering those effects on source apportionment using three dimensional air quality models. The WRF/Chem model was applied over the East Asia and northern China at 36 and 12 km horizontal grid resolutions, respectively, for the period of January 2013, with two sets of simulations with or without aerosol-meteorology feedbacks. The source contributions of power plants, industrial, domestic, transportation, and agriculture are evaluated using the Brute-Force Method （BFM） under the two simulation configurations. Our results indicate that, although the increases in PM2.5 concentrations due to those effects over the three southern Hebei cities are only 3%-9% on monthly average they are much more significant under high PM2.5 Ioadmgs （-50 gg.m - when PM25 concentrations are higher than 400μg.m^-3）. When considering the aerosol feedbacks, the contributions of industrial and domestic sources assessed using the BFM will obviously increase （e.g., from 30% 34% to 32%-37% for industrial）, especiallY3under high PM2.5 loadings （e.g., from 36%-44% to 43%-47% for domestic when PM2.5〉400μg·m^-3）. Our results imply that the aerosol direct effects should not be ignored during severe pollution episodes, especially in short-term source apportionment using the BFM.

All-Sky Direct Radiative Effects of Urban Aerosols in Beijing and Shanghai, China

Aerosol particles can directly alter the radiation balance by scattering and absorbing incident solar radiation, thus decreasing the amount of light reaching the surface and increasing the fraction of diffuse radiation—the so-called ‘aerosol direct radiative effect'. Using the Moderate Resolution Imaging Spectroradiometer aerosol products, the aerosol direct radiative effects under all-sky conditions in Beijing and Shanghai in 2007 were explored in this study. The total shortwave radiation was calculated using the Fu-Liou radiative transfer model, with the influence of clouds taken into account through sunshine-duration data, and the diffuse radiation was calculated with radiation decomposition models. Good correlation between measured and calculated total radiation was obtained at both cities, with an R greater than 0.9, and thus this calculation method was adopted to derive aerosol direct radiative effects. The presence of aerosols caused the mean total and diffuse solar radiation reaching the surface to change by-19.9% and +27.4% in Beijing, respectively, and by-18.4% and +6.5% in Shanghai. It was also found that, despite the strong negative correlation between aerosol optical depth and total radiation change, the diffuse radiation changes were determined predominantly by clouds. The effects of such changes induced by aerosols on plant productivity should be further studied.

Direct Climatic Effect of Dust Aerosol in the NCAR Community Atmosphere Model Version 3 (CAM3)

Direct climate responses to dust shortwave and longwave radiative forcing （RF） are studied using the NCAR Community Atmosphere Model Version 3 （CAM3）. The simulated RF at the top of the atmosphere （TOA） is-0.45 W m-2 in the solar spectrum and ＋0.09 W m-2 in the thermal spectrum on a global average. The magnitude of surface RF is larger than the TOA forcing, with global mean shortwave forcing of-1.76 W m-2 and longwave forcing of ＋0.31 W m-2 . As a result, dust aerosol causes the absorption of 1.1 W m-2 in the atmosphere. The RF of dust aerosol is predicted to lead to a surface cooling of 0.5 K over the Sahara Desert and Arabian Peninsula. In the meantime, the upper troposphere is predicted to become warmer because of the absorption by dust. These changes in temperature lead to a more stable atmosphere, which results in increases in surface humidity. The upward sensible and latent heat fluxes at the surface are reduced, largely balancing the surface energy loss caused by the backscattering and absorption of dust aerosol. Precipitation is predicted to decrease moderately on a global scale.

Simulating Aerosol Optical Depth and Direct Radiative Effects over the Tibetan Plateau with a High-Resolution CAS FGOALS-f3 Model

Current global climate models cannot resolve the complex topography over the Tibetan Plateau(TP)due to their coarse resolution.This study investigates the impacts of horizontal resolution on simulating aerosol and its direct radiative effect(DRE)over the TP by applying two horizontal resolutions of about 100 km and 25 km to the Chinese Academy of Sciences Flexible Global Ocean-Atmosphere Land System(CAS FGOALS-f3)over a 10-year period.Compared to the AErosol RObotic NETwork observations,a high-resolution model(HRM)can better reproduce the spatial distribution and seasonal cycles of aerosol optical depth(AOD)compared to a low-resolution model(LRM).The HRM bias and RMSE of AOD decreased by 0.08 and 0.12,and the correlation coefficient increased by 0.22 compared to the LRM.An LRM is not sufficient to reproduce the aerosol variations associated with fine-scale topographic forcing,such as in the eastern marginal region of the TP.The difference between hydrophilic aerosols in an HRM and LRM is caused by the divergence of the simulated relative humidity(RH).More reasonable distributions and variations of RH are conducive to simulating hydrophilic aerosols.An increase of the 10-m wind speed in winter by an HRM leads to increased dust emissions.The simulated aerosol DREs at the top of the atmosphere(TOA)and at the surface by the HRM are–0.76 W m^(–2)and–8.72 W m^(–2)over the TP,respectively.Both resolution models can capture the key feature that dust TOA DRE transitions from positive in spring to negative in the other seasons.

Impact of Direct Radiative Forcing of Anthropogenic Aerosols on Diurnal Temperature Range in January in Eastern China

This study investigates the changes in January diurnal temperature range(DTR) in China during 1961-2000.The observed DTR changes during 1981-2000 relative to 1961-80 are first analyzed based on the daily temperature data at 546 weather stations.These observed DTR changes are classified into six cases depending on the changes in daily maximum and minimum temperatures,and then the occurrence frequency and magnitude of DTR change in each case are presented.Three transient simulations are then performed to understand the impact of greenhouse gases(GHGs) and aerosol direct forcing on DTR change:one without anthropogenic radiative forcing,one with anthropogenic GHGs,and another one with the combined forcing of GHGs and five species of anthropogenic aerosols.The predicted daily DTR changes during the years 1981-2000 are also classified into six cases and are compared with the observations.Results show that the previously proposed reason for DTR reduction,a stronger nocturnal warming than a daytime warming,explains only 19.8%of the observed DTR reduction days.DTR reductions are found to generally occur in northeastern China,coinciding with significant regional warming.The simulation with GHG forcing alone reproduces this type of DTR reduction with an occurrence frequency of 32.9%,which is larger than the observed value.Aerosol direct forcing reduces DTR mainly by daytime cooling.Consideration of aerosol cooling improves the simulation of occurrence frequencies of different types of DTR changes as compared to the simulation with GHGs alone,but it cannot improve the prediction of the magnitude of DTR changes.

Climate Responses to Direct Radiative Forcing of Anthropogenic Aerosols,Tropospheric Ozone,and Long-Lived Greenhouse Gases in Eastern China over 1951–2000

A unified chemistry-aerosol-climate model is applied in this work to compare climate responses to changing concentrations of long-lived greenhouse gases （GHGs, CO2, CH4, N2O）, tropospheric O3, and aerosols during the years 1951-2000. Concentrations of sulfate, nitrate, primary organic carbon （POA）, secondary organic carbon （SOA）, black carbon （BC） aerosols, and tropospheric 03 for the years 1950 and 2000 are obtained a priori by coupled chemistry-aerosol-GCM simulations, and then monthly concentrations are interpolated linearly between 1951 and 2000. The annual concentrations of GHGs are taken from the IPCC Third Assessment Report. BC aerosol is internally mixed with other aerosols. Model results indicate that the sinmlated climate change over 1951-2000 is sensitive to anthropogenic changes in atmospheric components. The predicted year 2000 global mean surface air temperature can differ by 0.8℃ with different forcings. Relative to the climate simulation without changes in GHGs, O3, and aerosols, anthropogenic forcings of SO4^2-, BC, BC＋SO4^2-, BC＋SO4^2- ＋POA, BC＋SO4^2- ＋POA＋SOA＋NO3^-, O3, and GHGs are predicted to change the surface air temperature averaged over 1971-2000 in eastern China, respectively, by -0.40℃, ＋0.62℃, ＋0.18℃, ＋0.15℃, -0.78℃, ＋0.43℃, and ＋0.85℃, and to change the precipitation, respectively, by -0.21, ＋0.07, -0.03, ＋0.02, -0.24, -0.08, and ＋0.10 mm d^-1. The authors conclude that all major aerosols are as important as GHGs in influencing climate change in eastern China, and tropospheric O3 also needs to be included in studies of regional climate change in China.

气溶胶效应对北京一次暴雨过程影响的数值模拟研究

人为气溶胶对夏季强降水有重要影响,但其影响程度和相关机理仍具有极大不确定性。以2020年8月12—13日发生在北京的一次区域性暴雨过程为例,利用耦合了气溶胶-气象相互作用的WRF-Chem模式,基于敏感性试验探究了气溶胶直接效应、间接效应与总效应对此次暴雨过程的影响及机制。结果表明:(1)降水第一阶段(8月12日15∶00—18∶00)(北京时,下同),由于气溶胶对太阳辐射的消光及对云粒子的影响,气溶胶直接效应、间接效应和总效应均使得北京城区小时雨强减少,最大依次减少6 mm·h^(-1)、1 mm·h^(-1)和4 mm·h^(-1)。(2)降水第二阶段(8月12日20∶00—13日04∶00),气溶胶直接和间接效应也均使北京城区小时雨强减少,最大均减少约4 mm·h^(-1),气溶胶总效应对小时雨强影响不大,但使降水时间滞后。总体上,气溶胶直接效应使暖云过程增强、冷云过程减弱,从而减少降水并使第二阶段强降水过程提前;气溶胶间接效应使雨滴的有效半径降低,从而降低碰并过程,减少降水,并推迟第二阶段强降水的发生时间;气溶胶总效应对降水的影响是气溶胶直接和间接效应共同的非线性影响结果,在降水第一阶段以直接效应为主,第二阶段则以间接效应为主。

近60年西安日照时数变化特征及其影响因子分析

利用常规气象观测资料和MODIS卫星C5气溶胶产品,分析了近60年西安日照时数变化特征及其相关影响因子。结果表明,西安日照时数在1981-2001年之间存在明显的下降趋势,以春、夏季日照时数下降最为明显,秋、冬季次之。渭南、华县的日照时数变化表明,西安及其以东地区的日照时数存在区域性下降,且3个城市的日照时数下降百分率存在明显的相关性。而华山(海拔2064.9m)的日照时数在近几十年中并未出现明显的增加或减少趋势,因此,影响西安及其东部日照时数下降的原因很可能位于近地面2km以下。通过分析气溶胶光学厚度、总云量、低云量和降水量的变化,发现关中东部地区的气溶胶光学厚度明显高于西部地区,高浓度的气溶胶并未导致西安、渭南、华县3个城市的总云量、低云量和降水量的增加,相反云量和降水量均呈现弱的区域性下降趋势。因此,西安及其以东地区日照时数的区域性下降不是气溶胶的间接效应引起的,很可能是在地形和盛行风向的共同作用下导致气溶胶在关中东部地区堆积而产生的直接辐射效应所致。

硫酸盐气溶胶直接辐射效应对东亚副热带季风进程的影响

本文利用全球气候—大气化学模式CAM5并结合NCEP/NCAR(National Centers for Environmental Prediction/National Center for Atmospheric Research)1950～2009年再分析资料,讨论硫酸盐气溶胶直接辐射效应对东亚副热带季风爆发、发展和结束进程的影响。模拟结果表明:硫酸盐气溶胶通过直接辐射效应引起东亚大陆大部分地区近地面降温,进而降低了中纬度东亚大陆与西太平洋之间的纬向热力对比,延迟春初、提早夏末海陆纬向热力差异逆转时间,由此引发东亚副热带季风爆发时间延后了4候左右,结束时间提前了3候左右;减小的海陆热力差异导致东亚大陆偏南风减弱、东亚季风减弱以及季风降水的区域调整。我们通过NCEP/NCAR再分析资料分析亦发现,1980年以后中纬度东亚大陆与西太平洋之间的纬向热力差异逆转时间比1980年以前在春初延迟、夏末提前,导致了副热带季风爆发时间比1980年之前延后,结束时间提前,东亚大陆偏南风减弱,副热带夏季风系统性减弱,硫酸盐直接辐射效应可能是造成这一结果的原因之一。以往的观测和模拟都表明,由于人为活动的增加,导致1980年后东亚大陆硫酸盐气溶胶负荷较之前大幅增加,而东亚夏季风减弱,本文的研究进一步确认了两者间关系。

气溶胶直接气候效应对天津气象和空气质量的影响

基于在线大气化学模式WRF/chem,发挥其在线模式的优势,假设是否考虑气溶胶直接气候效应2种情况,模拟2015年全年天津地区气象场和空气质量的演变,并与观测实况比较,定量剖析天气-气溶胶-天气-空气质量之间的相互关系.结果表明:2015年气溶胶直接气候效应导致天津地面太阳辐射下降27.42W/m^2,气温下降0.21℃,风速减少1.1%,相对湿度增加1.4%,边界层高度下降6.3%,气象条件向不利于大气污染扩散方向转变,由于上述作用的存在,2015年PM_(2.5)质量浓度增加3μg/m^3,PM_(10)增加5.5μg/m^3,SO_2增加1.2μg/m^3,同时由于气溶胶影响光化学条件导致的O_3质量浓度减少1.4μg/m^3.气溶胶直接气候效应形成天气-气溶胶-天气-气溶胶之间的循环作用并不是线性的,重污染天气显著强于清洁日和平均条件,从而导致重污染天气空气质量的进一步恶化.

气象—化学双向耦合模式(WRF-NAQPMS)研制及其在京津冀秋季重霾模拟中的应用

为解析大气污染物与气象的双向反馈机制及其对气象和环境的影响,建立基于Mie散射理论的气溶胶—光学性质模块,研制气象-化学双向耦合器,以嵌套网格空气质量预报模式NAQPMS(Nested Air Quality Prediction Modeling System)为基础,建立了NAQPMS和中尺度气象模式WRF(Weather Research and Forecasting Model)的双向耦合模式(WRF-NAQPMS)。利用此模式数值模拟了2013年9月27日至10月1日的北京-天津-河北地区一次秋季严重灰霾过程。结果表明,考虑气溶胶辐射反馈的双向耦合模式模拟的气象要素和细颗粒物(PM2.5)浓度与观测结果更为一致。灰霾期间,气溶胶直接辐射效应显著改变了边界层气象要素,北京-天津-河北地区地面接收的太阳短波辐射减少25%,2 m高度的温度平均下降1°C,湍流动能下降20%,10 m高度的风速降低超过0.2 m/s,边界层高度下降25%,使得边界层大气更加静稳,进而造成了重污染地区污染进一步加剧,如石家庄近地面细颗粒物浓度增加可达30%。分析表明灰霾与边界层气象要素之间存在一种正反馈机制,采用该机制的双向耦合模式有利于准确模拟和预报灰霾污染过程。

人为气溶胶对中国东部冬季风影响的模拟研究

采用美国国家大气研究中心(NCAR)的公共大气模式CAM5.1研究了人为气溶胶排放增加对中国东部冬季风的影响,同时通过对比中国东部地区不同人为气溶胶排放源的敏感性试验结果,探讨了人为硫酸盐、黑碳及总人为气溶胶(硫酸盐+黑碳)增加对东亚冬季风的影响。结果表明:冬季硫酸盐气溶胶排放增加的直接和第一间接效应减少了到达地表的短波辐射通量,引起了陆地地表和对流层低层降温,海平面气压升高,增加了海陆间气压梯度,使得东亚冬季风增强。其第二间接效应导致中国南部大尺度降水率减少;黑碳气溶胶排放增加导致到达地表的短波辐射通量减少和大气中短波辐射通量增加,其半直接效应部分抵消了直接效应,故地表温度变化微小且不显著。加热的对流层低层导致中国南部对流活动和对流降水率增加;总人为气溶胶排放增加导致的大气温度变化表现为弱的降温作用,引起中国北部对流和大尺度降水率减少,而南部对流降水率增加。总人为气溶胶和黑碳气溶胶排放增加是导致中国北(南)部的东亚冬季风增强(减弱)的重要因素。

亚洲地区碳气溶胶的时空特征及其直接气候效应

利用耦合了陆面和化学过程的区域气候模式Reg CM4.0,对2000—2008年亚洲地区碳气溶胶的时空分布特征及其直接气候效应进行了模拟研究。结果表明:碳气溶胶在冬夏两季主要分布于印度半岛和我国中东部地区,其中印度半岛东北部和四川盆地地区为主要的大值区。夏季随着亚洲季风的爆发和雨季的到来,碳气溶胶的含量和分布范围较冬季有明显的减弱和北移。冬季碳气溶胶对整个亚洲地区的地表主要起冷却作用,而夏季在我国的四川盆地、华北和华南等地则出现了升温现象,这种局部升温现象与黑碳的"半直接效应"密切相关。碳气溶胶对降水影响的空间分布呈现出明显的地域不一致性,对南亚夏季风有一定的增强作用。东亚和南亚地区对碳气溶胶的气候响应存在较大差异,主要表现在夏季南亚地区低层降温、中高层增温,而东亚地区的增温却主要集中在低层。

人为气溶胶的直接辐射效应及其对南亚冬季风的影响

运用区域气候模式RegCM4.0(Regional Climate Model Verson 4.0)耦合入一个化学过程,对硫酸盐、黑碳、有机碳这3种人为气溶胶的时空分布特征和直接辐射效应进行了数值模拟,进而研究了气溶胶对南亚冬季风的影响。结果表明:光学厚度和地表短波辐射强迫的时空变化可能主要受硫酸盐气溶胶的影响。在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,大气层顶和地表的负短波辐射强迫分布与气溶胶分布基本一致,地表辐射强迫强度绝对值比大气层顶辐射强迫强度绝对值大得多。相关分析和合成分析表明:在南亚夏季风向冬季风转换时期和南亚冬季风盛行时期,南亚人为气溶胶主要分布区中的气溶胶柱浓度含量与南亚冬季风的建立和强度有反相关关系。这与气溶胶吸收太阳辐射,从而引起气温和位势高度的变化有关。

基于MODIS数据的长三角地区气溶胶直接辐射效应研究

以长三角地区为研究区,基于MODIS卫星遥感数据和6S大气辐射传输模型,模拟计算长三角地区地表和大气层顶的气溶胶直接辐射效应(aerosol direct radiation effect,ADRE),并利用南京信息工程大学北辰楼站点CE-318实测数据进行精度验证,在此基础上分析长三角地区气溶胶直接辐射效应的时空分布特征。结果表明,利用MODIS数据反演的地表ADRE、大气层顶ADRE与实测值的拟合精度R2分别为0.92和0.95。在空间上,地表与大气层顶直接辐射效应值的分布区域与变化趋势在整体上趋于一致,其绝对值均呈现北高南低的态势,地表ADRE为-31.60^-20.54 W·m-2、大气层顶ADRE为-3.48^-2.61 W·m-2之间的ADRE绝对值高值区主要集中在北部,尤其在江苏南部的苏州、无锡和常州地区,气溶胶辐射效应显著增大;在时间上,ADRE绝对值的年变化呈波动下降趋势,地表和大气层顶ADRE均值分别在-21.78^-5.94和-2.45^-0.73 W·m-2之间。其中江苏、上海地区气溶胶辐射效应的季节性变化明显,浙江地区辐射效应的季节性差异较小,地表ADRE变化范围大多分布在-10~0 W·m-2区间,大气层顶ADRE变化范围大多分布在-1~0 W·m-2区间。

东亚地区人为气溶胶直接辐射强迫及其气候效应的数值模拟

利用耦合化学过程的区域气候模式RegCM3,模拟研究3种主要人为排放气溶胶(硫酸盐、黑碳、有机碳)对东亚区域气候的影响。计算分析近20 a来3种气溶胶的时空分布、综合辐射强迫作用及其对地面气温和降水的影响。模拟结果表明:3种气溶胶冬夏季分布有所不同,冬季气溶胶大值区主要分布在南方地区,而夏季大值区北移;气溶胶短波辐射强迫在大气层顶和地面均为负值;气溶胶的加入对东亚地区地表气温有明显影响,冬季降温中心位于四川盆地,夏季降温大值区位于华北地区。气溶胶直接气候效应使得冬季东亚大部分地区降水减少,夏季东亚地区降水与中国南方地区夏季气溶胶浓度有较好的相关关系,中国东部雨带有南移趋势。

中国区域气溶胶对东亚夏季风的可能影响(I):硫酸盐气溶胶的影响

利用NCAR的新一代GCM CAM3.0模式离线耦合一个气溶胶同化系统,模拟研究了中国区域硫酸盐气溶胶的直接气候效应对东亚夏季风及其降水的影响。结果显示:中国区域硫酸盐气溶胶引起全球平均的直接辐射强迫为-0.25W/m2,中国内陆约25°N以北普遍降温,而海表温度升高。由此导致海陆温差缩小,东亚夏季风强度减弱,中国地区季风降水明显减少,而尤以积云降水减少起主要作用。硫酸盐气溶胶对中国地区的对流活动起抑制作用。

近50年来鄂尔多斯地面太阳辐射的变化及与相关气象要素的联系

根据部分气象台站1961—2006年期间的观测资料,分析了鄂尔多斯高原地面太阳辐射的年变化和年际变化特征,也联系该地区云量、降雨日数、能见度、沙尘暴日数和相对湿度等相关气象要素的资料的变化,分析了该地区太阳辐射变化的可能原因以及这些变化对该地区太阳能资源利用的影响。结果表明:鄂尔多斯高原地面太阳辐射的年变化与该地区天文辐射的变化基本一致,夏季的云量对太阳辐射的削弱作用最强,春季的沙尘气溶胶和较多的中高云量使该地区散射辐射的比例明显增加,而直接辐射的比例明显减少;近46年鄂尔多斯高原的地面太阳辐射量和直射比均呈总体减少的趋势,但在1992年以后略微增加。因太阳辐射变化的原因十分复杂,进一步更深入的研究是需要的。

基于MODIS和AERONET的气溶胶地表直接辐射效应评价

气候变化背景下进一步开展高污染地区气溶胶直接辐射效应的研究,对于该地区的大气环境监测、气候变化评估以及农业生产布局等具有重要意义。利用全球气溶胶监测网(AERONET)多年观测资料以及MODIS地表反照率数据,借助6S(Second Simulation of a Satellite Signal in the Solar Spectrum)辐射传输模式,定量评估2001年1月-2016年12月中国AERONET北京、香河和太湖3个典型高污染站点多年晴空条件下的气溶胶直接辐射效应。结果表明:(1)各个高污染站点气溶胶PM2.5质量浓度季节变化特征差异明显,秋冬污染较为严重,其中高值主要集中在1月、2月、11月和12月;(2)与无气溶胶影响相比,气溶胶致使各站点地表直接辐射年际变化较明显。在气溶胶影响下,北京、香河和太湖3个站点2001-2016年地表日平均直接辐射年际变化较明显,均呈波动增加趋势,且香河站日平均直接辐射增加最大(621.14W·m-2),太湖站次之(743.29W·m-2),北京站最小(488.14W·m-2)。(3)气溶胶影响下各站点地表直接辐射明显降低,且气溶胶对各站点影响差异较大。2001-2016年,北京、太湖和香河站年平均地表直接辐射分别降低32.29%、24.01%和15.07%。其中,气溶胶对北京站的地表直接辐射影响最大,香河站最小。(4)近15a来,北京、香河和太湖3个站点气溶胶地表辐射效应均呈现增加趋势。

硫酸盐气溶胶直接和间接辐射气候效应的模拟研究

将大气化学模式引入到区域气候模式中 ,实现同步计算大气化学成分和气象要素 ,以中国地区 1994年 1、4、7、10月为研究对象 ,模拟了 4个月的气候变化 ,通过分析发现 :硫酸盐气溶胶的直接和间接辐射效应都使大气顶产生负的辐射强迫 ,使地面气温下降 ;间接效应的引入加剧了辐射强迫和地面降温 ,是一个不可忽视的重要过程 。