Aerosol composition,sources,and secondary processing during autumn at a regional site in the Beijing-Tianjin-Hebei region

Air pollution is serious during autumn in the Beijing-Tianjin-Hebei(BTH)region,but there are few studies that have utilized real-time observations and source apportionment of the autumn submicron aerosols in this region.In this study,a quadrupole aerosol chemical speciation monitor(Q-ACSM)was deployed for the real-time measurement of the non-refractory compositions of submicron aerosols(NR-PM1)at a regional site(Xianghe)from October 3 to November 14,2017.The results showed that nitrate was the largest inorganic aerosol,and the oxygenated organic aerosol(OOA)was the largest organic aerosol in Xianghe.Hydrocarbon-like OA(HOA)was the largest organic aerosol When the NR-PM1 mass concentrations increased from the lowest to the highest bins,nitrate and biomass burning OA(BBOA)showed increasing trends in the suburban area.Enhanced nitrate formation during the pollution epi-sodes resulted from both photochemical and aqueous processing.To reduce the particulate matter(PM2.5)concentrations and eliminate heavy pollution episodes,control measures should focus on reducing NO_(x),NH_(3),and volatile organic compound(VOCs)emissions.

Hygroscopic growth of aerosol scattering coefficient:A comparative analysis between urban and suburban sites at winter in Beijing

A humidity controlled inlet system was developed to measure the hygroscopic growth of aerosol scattering coefficient in conjunction with nephelometry at an urban site of Chinese Academy of Meteorological Sciences (CAMS) in Beijing and a rural site at Shangdianzi Regional Background Air Pollution Monitoring Station (SDZ) outside Beijing during winter, from December 2005 to January 2006. Measurements were carried out at a wavelength of 525 nm with an Ecotech M9003 nephelometer. The hygroscopic growth function (or factor) of the aerosol scattering coefficient f(RH) increased continuously with increasing relative humidity (RH) and showed no obvious "step-like" deliquescent behavior at both sites during the experiment. The average growth factor f(RH) at the SDZ site could reach 1.5 when RH increased from less than 40% to 92%, and to 2.1 at the CAMS site when RH increased from less than 40% to 93%. The average hygroscopic growth factor at a relative humidity of 80%, f(RH = 80 ± 1%), was found to be about 1.26 ± 0.15 at CAMS and 1.24 ± 0.11 at SDZ. Further analysis indicated that under relatively polluted conditions, the average hygroscopic growth factor was higher at the CAMS site than that at the SDZ site. However, under relatively clean air conditions, the difference between the two sites was small, showing a hygroscopic growth behavior similar to those of burning biomass or blowing dust. These results reflected the different characteristics of aerosol types at the two sites.

PM_(2.5) and PM_(10-2.5) chemical composition and source apportionment near a Hong Kong roadway

Twenty-four-hour PM_(2.5) and PM_(10) samples were collected simultaneously at a highly trafficked roadside site in Hong Kong every sixth day from October 2004 to September 2005.The mass concentrations of PM_(2.5),PM_(10-2.5)(defined as PM_(10)- PM_(2.5)),organic carbon(OC),elemental carbon(EC),water-soluble ions,and up to 25 elements were determined.Investigation of the chemical compositions and potential sources revealed distinct differences between PM_(2.5) and PM_(10-2.5).The annual average mass concentrations were 55.5±25.5 and 25.9±15.7 ug/m^3 for PM_(2.5) and PM_(10-2.5),respectively.EC,OM(OM =OC×1.4),and ammonium sulfate comprised over ~82% of PM_(2.5),accounting for^29%,~27%,and ~25%,respectively,of the PM_(2.5) mass.Low OC/EC ratios(less than 1) for PM_(2.5) suggested that fresh diesel-engine exhaust was a major contributor.Seven sources were resolved for PM_(2.5) by positive matrix factorization(PMF) model,including vehicle emissions(~29%),secondary inorganic aerosols(~27%),waste incinerator/biomass burning(~23%),residual oil combustion(~10%),marine aerosols(~6%),industrial exhaust(~4%),and resuspended road dust(~1%).EC and OM comprised only ~19%of PM_(10-2.5).The average OC/EC ratio of PM_(10-2.5) was 7.8±14.2,suggesting that sources other than vehicular exhaust were important contributors.The sources for PM_(10-2.5) determined by the PMF model included ~20%traffic-generated resuspension(e.g.,tire dust/brake linear/petrol evaporation),~17% locally resuspended road dust,~17% marine aerosols,~12% secondary aerosols/field burning,and ~11%vehicle emissions.

Chemical properties and origin of dust aerosols in Beijing during springtime

Ground observation of dust aerosols was conducted in Beijing in the spring of 2005 in order to investigate the element composition and origin of mineral dust. Mass concentrations of most mineral elements of particles increased during dust events. Mineral elements were predominant in the sums of total element loadings in both dusty and non-dusty days. Mg, Si, Fe, Al or Ti can be used as an indicator of dust out?ow; Cl can be viewed as an evidence of dust particles mixing with anthropogenic emissions. Mineral and pollutant elements showed a bimodal mass particle-size distribution (MSD) in non-dusty days, and a trimodal distribution in dusty days, but their peak concentrations fell in different size stages. Zn and S were mainly enriched in fine particles, whereas Cl was enriched in medium particles, but most mineral elements and Cu were enriched in coarse particles. Mineral elements were dominated by crustal material in dusty even non-dusty days, but pollutant elements were from non-crustal material including local and remote sources. Back trajectory analysis indicated that dust particles in Beijing mainly originated from the Gobi and desert regions of Mongolian and northern China.

Impacts of aerosol chemical compositions on optical properties in urban Beijing,China

The optical properties of aerosols and their chemical composition,including water-soluble ions,organic carbon(OC),and elemental carbon(EC) in PM_(2.5) and PM_(10),were measured from 26 May to 30 June of 2012 at an urban site in Beijing.The daily average concentrations of PM_(2.5) and PM_(10) were 103.2 and 159.6 μg/m^3,respectively.On average,the OC and EC contributed 20.1% and 4.3% ,respectively,to PM_(2.5) and 16.3% and3.9% ,respectively,to PM_(10).Secondary ions(SO_4^(2-),NO_3^-,and NH_4^+) dominated the water-soluble ions and accounted for 57.9% and 62.6% of PM_(2.5) and PM_(10),respectively.The wind dependence of PM_(2.5),OC,SO_4^(2-),and NO_3^- implied that the pollution sources mainly came from south and southeast of Beijing during the summer.The monthly mean values of the scattering coefficient(σ_(sc)) and absorption coefficient(σ_(ab)) at525 nm were 312.9 and 28.7 Mm^(-1),respectively,and the mean single-scattering albedo(ω) was 0.85.The wind dependence of σ_(sc) revealed that this value was mainly influenced by regional transport during the summer,and the relationship between σ_(ab) and wind indicated that a high σ_(ab) resulted from the joint effects of local emissions and regional transport.The reconstructed σ_(sc) that was derived from the revised IMPROVE equation agreed well with the observations.The contribution of different chemical species toσ_(sc) was investigated under different pollution levels,and it was found that secondary inorganic aerosols accounted for a large part of σ_(sc) during pollution episodes(35.7% ),while organic matter was the main contributor to σ_(sc) under clean conditions(33.6% ).

Molecular distribution and seasonal variation of hydrocarbons in PM_(2.5) from Beijing during 2006

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Atmospheric Pb levels over Mount Qomolangma region

The Pb spectral concentration of atmospheric aerosol samples observed over Mount Qomolangma site (28°11′ 33″ N, 86°49′ 59″ E, 4950 m ASL) in 2002 was 13.3 ng/m3, about 4.5 times higher than that in 2000. The Pb spectral distribution showed three peaks, located at <0.25 m, 0.5-1 m, and 4-8 m in diameters. The peaks for <0.25 m and 0.25-0.5 m may be due to long-distant transport, while that for 4-8 m probably results from local floating dust. The atmospheric Pb concentration over Mount Qomolangma was lower than that of South Pole, most of the urban areas, and desert areas in the northern hemisphere. The enrichment factors for fine and coarse particles of atmospheric Pb in 2002 over Mount Qomolangma were 413.2 and 62.6, respectively, in support of the slight atmospheric pollution with Pb over the Qinghai-Tibetan Plateau.

Optical properties and chemical composition of PM_(2.5) in Shanghai in the spring of 2012

The semi-diurnal mean aerosol mass concentration, chemical composition, and optical properties of PM2.5were investigated in Shanghai during the spring of 2012. Slight pollution was observed during the study period. The average PM2.5 concentration was 64.11 土 22.83(xg/m3. The mean coefficients of extinction,scattering, and absorption at 532 nm were 125.9 士 78.5,91.1 士 56.3,and 34.9 士 23.6 Mm-1, respectively. A relatively low mean single scattering albedo at 532 nm(0.73 士 0.04) and low level of elemental carbon(EC,2.67 士 1.96 |xg/m3) suggested that the light absorption was enhanced due to the internal mixing of the EC.Sulfate contributed the most to aerosol light scattering in Shanghai. The chemical composition of PM2.5was dominated by particulate organic matter, sulfate, nitrate, ammonium, and EC. Anthropogenic sources made a significant contribution to the emission and loading of the particulate pollutants. A relatively good correlation between the aerosol chemical composition and the cloud condensation nuclei(CCN) activation indicated that aerosol chemistry is an important factor that influences the saturated hygroscopicity and growth of the aerosol.

Source,route and effect of Asian sand dust on environment and the oceans

We summarize in this overview achievements in current research frontiers in Asian sand dust with emphasis on the method for sand dust research,the sources of sand dust aerosols,emission of sand dust,mechanism of sand dust weather,chemical transformation during transport,and influences on climatic environment and oceans.Our main results show that most of Asian sand dust comes from Mongolia,the Gobi Desert,arid and semiarid desert areas in northwest China,which is divided into initial sources and enhanced sources.Half of the global production of dust originates from Asian dust source regions.Asian dust weather is so immense that it can cover a 5-7-day journey from the sources to the Korean Peninsula,Japan Islands,and the Pacific Ocean to even impact North America.Asian dust weather plays an active role in the biogeochemical cycles of trace elements in the mid-latitude Northern Hemisphere.

COMPARISON OF SIMULATING MINERAL DUST AEROSOLS IN EAST ASIA BY TWO EMISSION SCHEMES

Two common surface-dust emission schemes using critical wind speed and friction velocity were com-pared with the regional climate model RegCM3 in East Asia. In the comparison, transport of mineral dust and its distri-bution were simulated from March to April, 2001. Simulation results were also compared with TOMS aerosol index, showing that obvious differences exist in dust emission quantity and its column burden simulated by the dust emission schemes of friction velocity and wind speed criteria. The results obtained by the wind speed criterion are higher than that by friction velocity, bringing forth the problem whether or not the dust emission scheme matches the model. The obvious difference in the two schemes also explains the uncertainty of simulating mineral dust aerosol by modeling.

Simulation of the direct effects of dust aerosol on climate in East Asia

The results from some general circulation models show distinct radiative forcing(RF) by dust aerosol,which potentially has an effect on climate change.The direct RF and regional climatic effects of dust aerosol over the East Asian region are investigated in this study using NCAR's Community Atmospheric Model version 3.1.The negative RF at the top of the atmosphere(TOA) and the surface(SRF) has been revealed except for some high-albedo regions,which leads to a decrease in the surface air temperature and brings an increase of atmospheric radiative heating under both clear-and all-sky conditions.The decrease in the surface air temperature can be found over a wide region that includes the Indian peninsula and northwest China.It accompanies an increase in eastern China and the Korean peninsula,and temperature changes are not limited to regions with a large dust optical depth.A belt of vapor increase is revealed from the Indian peninsula extending east to northern China,while vapor content evidently deceases in southwest China.An increase in precipitation can also be found in the belt of increased vapor accompanying the reduction of precipitation across the regions to the south of 30oN.The pattern of rainfall change helps to offset the trend of increasing wetness in the south and increasing dryness in the north of China in recent years.