Simulation of the Radiative Effect of Black Carbon Aerosols and the Regional Climate Responses over China

As part of the development work of the Chinese new regional climate model (RIEMS), the radiative process of black carbon (BC) aerosols has been introduced into the original radiative procedures of RIEMS, and the transport model of BC aerosols has also been established and combined with the RIEMS model. Using the new model system, the distribution of black carbon aerosols and their radiative effect over the China region are investigated. The influences of BC aerosole on the atmospheric radiative transfer and on the air temperature, land surface temperature, and total rainfall are analyzed. It is found that BC aerosols induce a positive radiative forcing at the top of the atmosphere (TOA), which is dominated by shortwave radiative forcing. The maximum radiative forcing occurs in North China in July and in South China in April. At the same time, negative radiative forcing is observed on the surface. Based on the radiative forcing comparison between clear sky and cloudy sky, it is found that cloud can enforce the TOA positive radiative forcing and decrease the negative surface radiative forcing. The responses of the climate system in July to the radiative forcing due to BC aerosols are the decrease in the air temperature in the middle and lower reaches of the Changjiang River and Huaihe area and most areas of South China, and the weak increase or decrease in air temperature over North China. The total rainfall in the middle and lower reaches of the Changjiang River area is increased, but it decreased in North China in July.

SIMULATION OF SPATIO-TEMPORAL DISTRIBUTION CHARACTERISTICS AND RADIATIVE FORCING OF ORGANIC CARBON AEROSOLS IN CHINA

The International Centre for Theoretical Physics(ICTP,Italy) Regional Climate Model version 3.0(RegCM3) is used to simulate spatio-temporal distribution characteristics and radiative forcing(RF) of organic carbon(OC) aerosols in and around China.The preliminary simulation results show that OC aerosols are mostly concentrated in the area to the south of Yellow River and east of Tibetan Plateau.There is a decreasing trend of column burden of OC aerosols from south to north in China.The maximum value of column burden of OC aerosols is above 3 mg/m2 and located in the central and southern China,southeastern Tibet,and southwestern China's Yunnan,Guizhou,Sichuan provinces.The simulation on the seasonal variation shows that the maximum value of column burden of OC aerosols appears in winter and the secondary value is in spring and the minimum in summer.The RF of OC aerosols which varies seasonally is negative at the top of the atmosphere(TOA) and surface.The spatio-temporal characteristics of the RF of OC aerosols are basically consistent with that of IPCC,implying the high accuracy of the parameterization scheme for OC aerosols in RegCM3.

Seasonal variation of atmospheric elemental carbon aerosols at Zhongshan Station,East Antarctica

Elemental carbon(or black carbon)(EC or BC)aerosols emitted by biomass burning and fossil fuel combustion could cause notable climate forcing.Southern Hemisphere biomass burning emissions have contributed substantially to EC deposition in Antarctica.Here,we present the seasonal variation of EC determined from aerosol samples acquired at Zhongshan Station(ZSS),East Antarctica.The concentration of EC in the atmosphere varied between 0.02 and 257.81 ng·m^(-3)with a mean value of 44.87±48.92 ng·m^(-3).The concentration of EC aerosols reached its peak in winter(59.04 ng·m^(-3))and was lowest(27.26 ng·m^(-3))in summer.Back trajectory analysis showed that biomass burning in southern South America was the major source of the EC found at ZSS,although some of it was derived from southern Australia,especially during winter.The 2019–2020 Australian bush fires had some influence on EC deposition at ZSS,especially during 2019,but the contribution diminished in 2020,leaving southern South America as the dominant source of EC.

MORPHOLOGY OF BLACK CARBON AEROSOLS AND UBIQUITY OF 50-NANOMETER BLACK CARBON AEROSOLS IN THE ATMOSPHERE

Different-sized aerosols were collected by an Andersen air sampler to observe the detailed morphology of the black carbon （BC） aerosols which were separated chemically from the other accompanying aerosols, using a Scanning Electron Microscope equipped with an Energy Dispersive X-ray Spectrometer （SEM-EDX）. The results indicate that most BC aerosols are spherical particles of about 50 nm in diameter and with a homogeneous surface. Results also show that these particles aggregate with other aerosols or with themselves to form larger agglomerates in the micrometer range. The shape of these 50-nm BC spherical particles was found to be very similar to that of BC particles released from petroleum-powered vehicular internal combustion engines. These spherical BC particles were shown to be different from the previously reported fullerenes found using Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry （MALDI-TOF-MS）.

Modeled Influence of East Asian Black Carbon on Inter-Decadal Shifts in East China Summer Rainfall

Two inter-decadal shifts in East China summer rainfall during the last three decades of the 20th century have been identified.One shift occurred in the late 1970s and featured more rainfall in the Yangtze River valley and prolonged drought in North China.The other shift occurred in the early 1990s and featured increased rainfall in South China.The role of black carbon(BC) aerosol in the first shift event is controversial,and it has not been documented for the second event.In this study,the authors used Geophysical Fluid Dynamics Laboratory's(GFDL's) atmospheric general circulation model known as Atmosphere and Land Model(AM2.1) ,which has been shown to capture East Asian climate variability well,to investigate these issues by conducting sensitive experiments with or without historical BC in East Asia. The results suggest that the model reproduces the first shift well,including intensified rainfall in the Yangtze River and weakened monsoonal circulation.However,the model captures only a fraction of the observed variations for the second shift event.Thus,the role of BC in modulating the two shift events is different,and its impact is relatively less important for the early 1990s event.

Characterization of Black Carbon in the Ambient Air of Agra,India:Seasonal Variation and Meteorological Influence

This study characterizes the black carbon in Agra, India home to the Taj Mahal--and situated in the lndo-Gangetic basin. The mean black carbon concentration is 9.5 μg m-3 and, owing to excessive biomass/fossil fuel combustion and automobile emissions, the concentration varies considerably. Seasonally, the black carbon mass concentration is highest in winter, probably due to the increased fossil fuel consumption for heating and cooking, apart from a low boundary layer. The nocturnal peak rises prominently in winter, when the use of domestic heating is excessive. Meanwhile, the concentration is lowest during the monsoon season because of the turbulent atmospheric conditions and the process of washout by precipitation. The ratio of black carbon to brown carbon is less than unity during the entire study period, except in winter （December）. This may be because that biomass combustion and diesel exhaust are major black carbon contributors in this region, while a higher ratio in winter may be due to the increased consumption of fossil fuel and wood for heating purposes. ANOVA reveals significant monthly variation in the concentration of black carbon; plus, it is negatively correlated with wind speed and temperature. A high black carbon mass concentration is observed at moderate （1-2 m s-1） wind speed, as compared to calm or turbulent atmospheric conditions.

THE DIRECT EFFECTS OF AEROSOLS AND DECADAL VARIATION OF GLOBAL SEA SURFACE TEMPERATURE ON THE EAST ASIAN SUMMER PRECIPITATION IN CAM3.0

Using the CAM3.0 model, we investigated the respective effects of aerosol concentration increasing and decadal variation of global sea surface temperature(SST) around year 1976/77 on the East Asian precipitation in boreal summer. By doubling the concentration of the sulfate aerosol and black carbon aerosol separately and synchronously in East Asia(100-150 °E, 20-50 °N), the climate effects of these aerosols are specifically investigated. The results show that both the decadal SST changing and aerosol concentration increasing could lead to rainfall decreasing in the center of East Asia, but increasing in the regions along southeast coast areas of China. However, the different patterns of rainfall over ocean and lower wind field over Asian continent between aerosol experiments and SST experiments in CAM3.0 indicate the presence of different mechanisms. In the increased aerosol concentration experiments, scattering effect is the main climate effect for both sulfate and black carbon aerosols in the Eastern Asian summer. Especially in the increased sulfate aerosol concentration experiment, the climate scattering effect of aerosol leads to the most significant temperature decreasing, sinking convection anomalies and decreased rainfall in the troposphere over the central part of East Asia. However, in an increased black carbon aerosol concentration experiment, weakened sinking convection anomalies exist at the southerly position. This weakened sinking and its compensating rising convection anomalies in the south lead to the heavy rainfall over southeast coast areas of China. When concentrations of both sulfate and black carbon aerosols increase synchronously, the anomalous rainfall distribution is somewhat like that in the increased black carbon concentration aerosol experiment but with less intensity.

Examination of the Quality of GOSAT/CAI Cloud Flag Data over Beijing Using Ground-based Cloud Data

It has been several years since the Greenhouse Gases Observing Satellite （GOSAT） began to observe the distribution of CO2 and CH4 over the globe from space. Results from Thermal and Near-infrared Sensor for Carbon Observation-Cloud and Aerosol Imager （TANSO-CAI） cloud screening are necessary for the retrieval of CO2 and CH4 gas concentrations for GOSAT TANSO-Fourier Transform Spectrometer （FTS） observations. In this study, TANSO-CAI cloud flag data were compared with ground-based cloud data collected by an all-sky imager （ASI） over Beijing from June 2009 to May 2012 to examine the data quality. The results showed that the CAI has an obvious cloudy tendency bias over Beijing, especially in winter. The main reason might be that heavy aerosols in the sky are incorrectly determined as cloudy pixels by the CAI algorithm. Results also showed that the CAI algorithm sometimes neglects some high thin cirrus cloud over this area.

MODELING OF ORGANIC CARBON AEROSOL DISTRIBUTIONS OVER EAST ASIA IN THE SPRINGTIME

The Models-3 Community Multi-scale Air Quality (CMAQ) modeling system coupled with the Regional Atmospheric Modeling System (RAMS) is applied to East Asia to investigate the transport and evolution processes of organic carbon (OC) aerosols in the springtime of 2001. The simulated OC mixing ratios are compared with ground level observations at three remote sites in Japan during the Aerosol Characterization Experiment Asia (ACE-Asia) field campaign. It is found that the modeled OC concentrations are generally in good agreement with the observed ones, and the model reproduces the time variations in OC mixing ratios reasonably well. Model results show that high levels (larger than 16 mg.m-2) of column burden of OC aerosols concentrated in the middle reaches of Yangtse River and southern China, and that in most regions of China to the south of Yellow River the column burden was over 7 mg.m-2, while the isopleth of 4 mg.m-2 extended to the inner area of northwestern Pacific Ocean.

Observation of black carbon aerosol in Beijing, 2003

The objective of this study was to determine the black carbon concentration in Beijing in 2003.The aerosol properties were measured using an Aethalometer and a tapered element oscillating microbalance(TEOM)on the roof of the Physics Building of Peking University(39.99°N,116.31°E)from July to August 2003 and from November 2003 to January 2004.The average black carbon(BC)concentrations in the summer and winter were 8.80 and 11.4μg/m3,respectively.During winter,two different cyclone cut offs were installed at the inlet of an aethalometer.The BC mass concentration in TSP,PM_(10),and PM_(2.5)were obtained.The results indicated that in winter aerosol,90%of BC exited in PM_(10)and 82.6%of BC exited in PM_(2.5).The BC in PM_(10)accounted for 5.11%of the PM_(10)mass.