Variation of sulfate aerosol concentrations over the western Pacific and their effect on clouds, radiation and precipitation

Under bilateral cooperation between the United States of America and the People's Republic of China, a series of research cruises were conducted over the western Pacific Ocean. It was found that a) the non-sea-salt sulfate aerosol particles are the major source of cloud condensation nuclei, b) the population of clouds and the total albedo are proportional to the concentration of condensation nuclei and consequently to the concentration of the non-sea-salt aerosol particles, and c) the amount of rainfall is inversely proportional to the concentration of non-sea-salt sulfate aerosol particles. It seems that anthropogenic sulfate aerosol particles affect the regional planetary albedo and climate and that the contribution from biogenically derived sulfate aerosol particles is of lesser importance.

CHARACTERISTICS OF BOUNDARY LAYER AND ITS EFFECTS ON ATMOSPHERIC AEROSOL CONCENTRATIONS IN DONGGUAN, GUANGDONG

The structure of atmospheric boundary layer determines the ability of atmospheric dispersion and has an essential impact on airborne aerosols.In this paper,the data of a radio sounding experiment held in Dongguan National Meteorological Observation Station,which is in a coastal city in Pearl River Delta,as well as the data of atmospheric aerosols,were utilized in order to analyze the characteristics of atmospheric boundary layer and its effects on surface aerosol concentrations.The results are showed at follows:the local circulations,associated with dominant winds,made complex structures of atmospheric layers,as the cold air and systematic winds weakened in the end of a cold air event.Weakened wind shears and inversion layers,especially a strong near-surface inversion layer,remarkably diminished the atmospheric diffusion abilities and facilitated an especially high concentration of surface aerosols.The convergence line or weak shear line of sea breeze in the ground level helps weaken the atmospheric diffusion abilities and results in atmospheric aerosols accumulation.

Effect of Varying Aerosol Concentrations and Relative Humidity on Visibility and Particle Size Distribution in Urban Atmosphere

Atmospheric aerosol concentrations have been found to change constantly due to the influence of source,winds and human activities over short time periods.This has proved to be a constraint to the study of varied aerosol concentrations in urban atmosphere alongside changing relative humidity and how it affects visibility and aerosol particle size distribution.In this research simulation was carried out using Optical Properties of Aerosols and Clouds(OPAC 4.0)average concentration setup for relative humidity(RH)0-99%at visible wavelength 0.4-0.8μm to vary the concentrations of three aerosol components:WASO(Water-soluble),INSO(Insoluble)and SOOT.The Angstrom exponents(α),the curvatures(α2)and atmospheric turbidities(β)were obtained from the regression analysis of Kaufman’s first and second order polynomial equations for visibility.The research determined the mean exponent of the aerosol size growth curve(μ)from the effective hygroscopic growth(geff)and the humidification factors(γ)from visibility enhancement f(RH,λ).The mean exponent of aerosol size distributions(υ)was determined fromμandγ.The results showed that with varied WASO,INSO and SOOT concentrations respectively at different RH,aerosol particle size distributions showed bimodal characteristics with dominance of fine mode particles.Hazy atmospheric conditions prevailed with increasing turbidity.

VERTICAL DISTRIBUTION OF ATMOSPHERIC AEROSOL CONCENTRATION AT XIANGHE

This paper summarizes atmospheric aerosol concentrations of 5 stratospheric balloon soundings during the period from 1984 to 1994. Aerosol-rich layers in the troposphere were detected and the causes were analyzed. The main results are as follows: (1) the vertical distribution of the atmospheric aerosol is affected by atmospheric dynamic processes, humidity, etc.; (2) the tropospheric column concentrations of aerosol were 72.2×105, 20.2×105, 20.7×105 and 34.4×105 cm-2 and occupying 81%, 61% and 60% of the 0-to-30 km aerosol column, on Aug. 23, 1984, Aug. 22, 1993, Sept. 12, 1993 and Sept. 15, 1994, respectively; (3) the effect of volcano eruption was still evident in the aerosol profiles, 28 and 27 months after the El Chichon and Pinatubo eruption; (4) the aerosol concentration in the troposphere did not decrease at all heights as atmospheric aerosol model.

Ground-Based In Situ Measurements of Near-Surface Aerosol Mass Concentration over Anantapur:Heterogeneity in Source Impacts

Surface measurements of aerosol physical properties were made at Anantapur （14.62°N, 77.65°E, 331 m a.s.l）, a semiarid rural site in India, during August 2008-July 2009. Measurements included the segregated sizes of aerosolsas as well as total mass concentration and size distributions of aerosols measured at low relative humidity （RH〈75%） using a Quartz Crystal Microbalance （QCM） in the 25-0.05 um aerodynamic diameter range. The hourly average total surface aerosol mass concentration in a day varied from 15 to 70 ug m-3, with a mean value of 34.02±9.05 ug m-3 for the entire study period. A clear diurnal pattern appeared in coarse, accumulation and nucleation-mode particle concentrations, with two local maxima occurring in early morning and late evening hours. The concentration of coarse-mode particles was high during the summer season, with a maximum concentration of 11.81±0.98 ug m-3 in the month of April, whereas accumulationmode concentration was observed to be high in the winter period contributed 〉68% to the total aerosol mass concentration. Accumulation aerosol mass fraction, Af （= Ma/Mt） was highest during winter （mean value of Af -0.80） and lowest （Af - 0.64） during the monsoon season. The regression analysis shows that both Reff and Rm are dependent on coarse-mode aerosols. The relationship between the simultaneous measurements of daily mean aerosol optical depth at 500 nm （AOD500） and PM2.5 mass concentration （[PM2.5]） shows that surface-level aerosol mass concentration increases with the increase in columnar aerosol optical depth over the observation period.

Preliminary study on concentrations and size distribution of marine aerosols over the East China Sea

In summer and winter, 1987,and in spring and autumn, 1988, the concentrations and size distribution of marine aerosols were measured over the East China Sea and the South Japan Sea. This paper deals with the study on the seasonal variation of the marine aerosols with the meteorological parameters, the differences and the relations between the marine and continental aerosols. The results show that the marine aerosol concentrations and size distribution over the East China Sea have distinct seasonal change characteristics, which may be attributed to the East Asian atmospheric circulation. The size distribution is discussed by using a three-parameter size distribution model.

Simulated seasonal variations in nitrogen wet deposition over East Asia

The regional air quality modeling system Regional Atmospheric Modeling System–Community Multiscale Air Quality was applied to estimate the spatial distribution and seasonal variation in nitrogen wet deposition over East Asia in 2010. The simulated results were evaluated by comparing modeled precipitation rates and ion concentrations, such as ammonium（NH_4~＋）, nitrate（NO_3^-）, and sulfate, in rainwater, against observations obtained from Acid Deposition Monitoring Network in East Asia and meteorological stations in China. Comparison of simulated and observed precipitation showed that the modeling system can reproduce seasonal precipitation patterns reasonably well. For major ion species, the simulated results in most cases were in good agreement with those observed. Analysis of the modeled wet deposition distributions indicated that China experiences noticeable variation in wet deposition patterns throughout the year. Nitrogen wet deposition（NH_4~＋ ＋ NO_3^-） during summer and spring accounted for 71% of the annual total（3.9 Tg N yr^（-1））, including 42.7% in summer. Precipitation plays a larger role in the seasonal variation of wet deposition; whereas, aerosol concentrations affect its distribution patterns. In China, the amount of annual nitrogen wet deposition ranged from 1 to 18 kg N ha^（-1）. Nitrogen in wet deposition was mainly in the form of NH_4~＋, accounting for 65.76% of the total amount, and the molar ratio of NH_4~＋∕NO_3^- was mostly more than 1, indicating a relatively larger effect from agricultural activities.

A model for aerosol mass concentration using an optical particle counter

A model for measuring aerosol mass concentration by an optical particle counter is presented using the conception of the average mass. In this model, to understand the meaning of the pulse height distribution of particles which is used to inverse mass concentration, the relationship among intensity distribution in the optical sensing volume, particle shape, and the pulse height distribution is discussed. To solve the instability of the equivalent factor, a novel two-step calibration method is proposed. The experimental results demonstrate that mass concentrations calculated by the model are in good agreement with those measured by a norm-referenced instrument. For samples of soot and air, the slopes of fitting lines of data points are 0.9582 and 0.9220, and the correlation coefficients are 0.9991 and 0.9965, respectively.

Development of a portable reference aerosol generator （PRAG） for calibration of particle mass concentration measurements

The tapered element oscillating microbalance with filter dynamics measurement system （TEOM-FDMS） is an instrument commonly employed by the French air quality monitoring network. This instrument is currently calibrated with calibration weights traceable to SI but having value and mass differences between each of them that are not representative of real atmospheric particle mass measurements. Moreover, these calibration weights do not allow detection of any technical problems associated with either the TEOM-FDMS sampling system upstream of the mass measurement or the intrinsic TEOM-FDMS filtration system. Therefore, a calibration method was developed using a portable reference aerosol generator （PRAG） that produces known and stable particle mass concentrations over time. Here, we present the characterization of the PRAG system in terms of a reference range of particle masses between 30 - 10 and 3456 ± 83 μg at three sampling times. Its coupling with the TEOM-FDMS and a global comparison between the defined reference range of particle masses and the measured masses obtained with each TEOM-FDMS implicated in this study are also presented.

Origin of high particle number concentrations reaching the St. Louis, Midwest Supersite

Ultrafine particles are associated with adverse health effects. Total Particle Number Concentration（TNC） of fine particles were measured during 2002 at the St. Louis — Midwest supersite. The time series showed overall low level with frequent large peaks. The time series was analyzed alongside criteria pollutant measurements and meteorological observations. Multiple regression analysis was used to identify further contributing factors and to determine the association of different pollutants with TNC levels. This showed the strong contribution of sulfur dioxide（SO2） and nitrogen oxides（NO x） to high TNC levels. The analysis also suggested that increased dispersion resulting from faster winds and higher mixing heights led to higher TNC levels. Overall, the results show that there were intense particle nucleation events in a SO2 rich plume reaching the site which contributed around 29% of TNC. A further 40% was associated with primary emissions from mobile sources. By separating the remaining TNC by time of day and clear sky conditions,we suggest that most likely 8% of TNC are due to regional nucleation events and 23% are associated with the general urban background.

Evaluation of the influence of El Niño–Southern Oscillation on air quality in southern China from long-term historical observations

Previous studies demonstrated that the El Niño–Southern Oscillation(ENSO)could modulate regional climate thus influencing air quality in the low-middle latitude regions like southern China.However,such influence has not been well evaluated at a long-term historical scale.To filling the gap,this study investigated two-decade(2002 to 2020)aerosol concentration and particle size in southern China during the whole dynamic development of ENSO phases.Results suggest strong positive correlations between aerosol optical depth(AOD)and ENSO phases,as low AOD occurred during El Niño while high AOD occurred during La Niña event.Such correlations are mainly attributed to the variation of atmospheric circulation and precipitation during corresponding ENSO phase.Analysis of the angstrom exponent(AE)anomalies further confirmed the circulation pattern,as negative AE anomalies is pronounced in El Niño indicating the enhanced transport of sea salt aerosols from the South China Sea,while the La Niña event exhibits positive AE anomalies which can be attributed to the enhanced import of northern fine anthropogenic aerosols.This study further quantified the AOD variation attributed to changes in ENSO phases and anthropogenic emissions.Results suggest that the long-term AOD variation from 2002 to 2020 in southern China is mostly driven(by 64.2%)by the change of anthropogenic emissions from 2002 to 2020.However,the ENSO presents dominant influence(70.5%)on year-to-year variations of AOD during 2002–2020,implying the importance of ENSO on varying aerosol concentration in a short-term period.