Lidar Measurements of Aerosols in the Tropical Atmosphere

Measurements of atmospheric aerosols and trace gases using the Laser radar (lidar) techniques, have been in pro-gress since 1985 at the Indian Institute of Tropical Meteorology, Pune (18o32’N, 73o51’E, 559 m AMSL), India. These observations carried out during nighttime in the lower atmosphere (up to 5.5 km AGL), employing an Argon ion / Helium-Neon lidar provided information on the nature, size, concentration and other characteristics of the constituents present in the tropical atmosphere. The time-height variations in aerosol concentration and associated layer structure exhibit marked differences between the post-sunset and pre-sunrise periods besides their seasonal va-riation with maximum concentration during pre-monsoon / winter and minimum concentration during monsoon months. These observations also revealed the influence of the terrain of the experimental site and some selected me-teorological parameters on the aerosol vertical distributions. The special observations of aerosol vertical profiles ob-tained in the nighttime atmospheric boundary layer during October 1986 through September 1989 showed that the most probable occurrence of mixing depth lies between 450 and 550 m, and the multiple stably stratified aerosol lay-ers present above the mixing depth with maximum frequency of occurrence at around 750 m. This information on nighttime mixing depth / stable layer derived from lidar aerosol observations showed good agreement with the height of the ground-based shear layer / elevated layer observed by the simultaneously operated sodar at the lidar site.     

Effects of tropospheric aerosols on the solar radiative heating in a clear atmosphere

Summary The broadband solar absorptivity concept is employed to parameterize the aerosol absorption effect. The solar radiation model developed by Liou and his associates was modified to incorporate the parameterization of solar radiative transfer in an aerosol layer. Comparison of the results from this method with other schemes exhibits close agreement. A Sahara dust storm case was also chosen to test the performance of the present model, and the computed heating rate profiles agree well with calculations based on optical properties derived from observations for both clear and dust cases. In general, enhanced heating due to aerosol absorption of solar flux occurs particularly in the lower troposphere (below 5 km). The heating rate is independent of the scattering partition factor (), but the planetary albedo increases with . Further study shows that the aerosol heating is sensitive to the surface albedo (r _s ) and to the cosine of the solar zenith angle (µ ₀). The decrease inr _s and/or increase inµ ₀ lower the solar heating rate, the planetary albedo and the atmospheric absorptivity, but raise the surface absorptivity due to reduced multiple reflection between the atmosphere and surface.With 9 Figures     

北京城区北部冬、夏季大气颗粒物化学成分和粒度分布

1987年1,3月和6,8月在北京师范大学主楼顶上,用单孔级联碰撞采样器收集了大气颗粒物样品,用PIXE方法进行了分析,得到了冬、夏季19种元素的浓度和粒度分布,并对大气颗粒物中元素的主要来源进行了探讨。     

Correlation of atmospheric visibility with chemical composition of Kaohsiung aerosols

The objective of this study was to investigate the correlation of visibility with chemical composition of Kaohsiung aerosols. Daytime visibility was observed around noon at two observation sites in metropolitan Kaohsiung, Taiwan in the years of 1999 and 2000. Both seasonal and diurnal variation patterns of visibility were observed in the region. Ambient aerosols were sampled and analyzed for 11 constituents, including water-soluble ionic species (Cl⁻, NO₃⁻, SO₄⁻², NH₄⁺, K⁺, Na⁺, Ca⁺², and Mg⁺²) and carbonaceous contents (OC, EC, and TC), to characterize the chemical composition of Kaohsiung aerosols. Furthermore, a stepwise multiple linear regression model was developed to elucidate the influence of aerosol species on visibility impairments. The results showed that sulfate was the dominant species that affected both light scattering coefficient and visibility. On average, the percentage contributions of visibility degrading species to light scattering coefficient were 29% for sulfate, 28% for nitrate, 22% for total carbon, and 21% for PM_2.5-remainder. An empirical regression model of visibility based on sulfate, nitrate, and relative humidity was also developed. The model showed that sulfate in PM_2.5 was the most sensitive species to visibility variation, suggesting that the reduction of sulfate in PM_2.5 could effectively improve the visibility of metropolitan Kaohsiung. During the investigation period, an event of Asian dusts intruded metropolitan Kaohsiung and dramatically increased the aerosol loadings, especially in the coarse particles. However, local visual air quality did not degrade accordingly during the Asian dust event because both visibility and light scattering coefficient are affected mainly by the fine particles. The results are discussed in detail in the paper.     

Correlation of atmospheric visibility with chemical composition of Kaohsiung aerosols

The objective of this study was to investigate the correlation of visibility with chemical composition of Kaohsiung aerosols. Daytime visibility was observed around noon at two observation sites in metropolitan Kaohsiung, Taiwan in the years of 1999 and 2000. Both seasonal and diurnal variation patterns of visibility were observed in the region. Ambient aerosols were sampled and analyzed for 11 constituents, including water-soluble ionic species (Cl⁻, NO₃⁻, SO₄⁻², NH₄⁺, K⁺, Na⁺, Ca⁺², and Mg⁺²) and carbonaceous contents (OC, EC, and TC), to characterize the chemical composition of Kaohsiung aerosols. Furthermore, a stepwise multiple linear regression model was developed to elucidate the influence of aerosol species on visibility impairments. The results showed that sulfate was the dominant species that affected both light scattering coefficient and visibility. On average, the percentage contributions of visibility degrading species to light scattering coefficient were 29% for sulfate, 28% for nitrate, 22% for total carbon, and 21% for PM_2.5-remainder. An empirical regression model of visibility based on sulfate, nitrate, and relative humidity was also developed. The model showed that sulfate in PM_2.5 was the most sensitive species to visibility variation, suggesting that the reduction of sulfate in PM_2.5 could effectively improve the visibility of metropolitan Kaohsiung. During the investigation period, an event of Asian dusts intruded metropolitan Kaohsiung and dramatically increased the aerosol loadings, especially in the coarse particles. However, local visual air quality did not degrade accordingly during the Asian dust event because both visibility and light scattering coefficient are affected mainly by the fine particles. The results are discussed in detail in the paper.     

Formation and chemical composition of atmospheric aerosols in an equatorial forest area

The physical properties and the chemical composition of atmospheric aerosols have been studied in an equatorial region in the southern Congo (Africa). Field experiments were conducted between 1978 and 1983 in the equatorial forest of the Mayombe during periods where the influence of biomass burning was minimum. The results indicate that the forest is a net source of both fine particles resulting primarily from gas-to-particle conversion and coarse particles produced by mechanical processes. Carbonaceous matter is the major component of these biogenic particles but the forest is also a significant source of sulfate, nitrate, ammonium and potassium. Half of this carbon is attached to submicron particles and likely derives from organic gaseous precursors naturally emitted by the local biosphere.Presented at the international Symposium Influence of marine and terrestrial biosphere on the chemical composition of the atmosphere, held in Mainz, F.R.G., on 16–22 March 1986.     

A comparison analysis of chemical composition of aerosols in the dust and non-dust periods in Beijing

Dust events occurred frequently in Beijing in recent years. In this work, 120 aerosol samples werecollected in two typical dust events (21-22 March and 15 May) and a non-dust period in Beijing fromMarch to May 2001. Samples were analyzed for major elemental components by the Proton Induced X-ray Emission (PIXE) method. Results show that the enrichment factors of crustal elements such as Mg,A1, and Ti had little differences between the dust period and the non-dust period in Beijing, while theenrichment factors of other elements that have a relation to anthropogenic emissions were very low duringthe dust period. The results derived by using multivariate factor analysis from the observation data showthat the sources such as soil dust, industry, and fuel combustion were among the major contributors tothe particles in Beijing.     

Chemical components of lower tropospheric aerosols in the high arctic: Six years of observations

Six years of observations (1980 to 1986) of the composition of lower tropospheric aerosols at Alert on northern Ellesmere Island in the Canadian high Arctic yield insight into the seasonal variation of Arctic air pollutants as well as of substances of natural origin. A principal component analysis of 138 observations of 21 aerosol constituents (major ions, metals, nonmetallic trace elements) for the most polluted period of December to April identified not only a soil, sea salt and anthropogenic aerosol component, but also one associated with photochemical reactions in the atmosphere that occur at polar sunrise. Depending on the source of their gaseous precursors, elements in the photochemical component can be natural or anthropogenic in origin. For instance, SO₄ ^2-, existing mostly as H₂SO₄, originates probably from both anthropogenic and natural sources while Br^– is likely of marine origin. In contrast, SO₄ ^2- in the anthropogenic component has the stoichiometry of NH₄HSO₄. In the winter months, over 90% of Arctic SO₄ ^2- is in the anthropogenic and photochemical components.In winter, a substantial portion (11 to 35%) of Na⁺ is associated with the anthropogenic aerosol component suggesting either that marine aerosols have been physically or chemically modified by interactions with air pollution or that there are anthropogenic sources of Na⁺.The aerosol soil component is controlled by both local and distant dust sources. During a year, it has two peaks at Alert, one in April/May coinciding with the Asian dust storm season and one in September.There is a marked difference in the seasonal variation of particulate Br^– and iodine concentrations in the air. Both have a peak in April/May associated with polar sunrise and, hence, photochemical reactions in the atmosphere. However, iodine also peaks in early fall. This may be a product of biogenic iodine emissions to the atmosphere during secondary blooms in northern oceans in late summer.Presented at the Second Conference on Baseline Observations in Atmospheric Chemistry (SABOAC II) in Melbourne, Australia, November 1988     

Chemical characterization of water-soluble aerosols in different residential environments of semi aridregion of India

This paper deals with the atmospheric concentrations of PM₅ and PM_2.5 particulate matter and its water soluble constituents along with the size distribution of ions and spatial variation at three different residential environments in a semiarid region in India. Samples were collected from the indoors and outdoors of urban, rural and roadside sites of Agra during October 2007–March 2008. The mean concentrations of PM_2.5 indoors and outdoors were 178 μgm⁻³ and 195 μgm⁻³ while the mean concentrations of PM₅ indoors and outdoors were 231.8 μgm⁻³ and 265.2 μgm⁻³ respectively. Out of the total aerosol mass, water soluble constituents contributed an average of 80% (33% anions, 50% cations) in PM₅ and 70% (29% anions, 43% cations) in PM_2.5. The indoor–outdoor ratio of water soluble components suggested additional aerosol indoor sources at rural and roadside sites. Indoor–outdoor correlations were also determined which show poor relationships among concentrations of aerosol ions at all three sites. Univariate Pearson correlation coefficients among water soluble aerosols were determined to evaluate the relationship between aerosol ions in indoor and outdoor air.     

Chemical composition of dew in Amman, Jordan

Twenty-six dew samples were collected on a glass surface from an urbanized area in Amman city during the period October 1999 to June 2000. They were analyzed for the major ions (Cl, SO₄, NO₃, Ca, Mg, Na, K and NH₄) in addition to three heavy metals (Pb, Cd and Co). Rain samples were collected for the same period and compared to the chemical constituents of dew.It was found that both rain and dew samples were of almost neutral acidity due to the buffering effect of CaCO₃. Dew composition was mainly from CaSO₄ solution due to conversion of CaCO₃ to CaSO₄ when left exposed to a sulfate-rich atmosphere. The total dissolved solids were higher in dew than rain samples of the same period. This was attributed to higher evaporation effect on dew than rain.The heavy metal content in dew is highest during the cold winter season (December–March) due to excess fossil fuel combustion for heating purposes in this period. The heavy metal content in dew was lower than that for rain during the same period because of the shorter period of dew formation than rainwater.     

Size distribution and chemical composition of summer aerosols over Southern Ocean and the Antarctic region

Journal of Atmospheric Chemistry - The size distribution of atmospheric aerosols together with their composition, sources and sinks, is a key element in understanding aerosol effects on the...     

Chemical composition of precipitation and snow cover in the Primorsky krai

The chemical composition ofprecipitation from May 2012 to March 2013 and snow cover in the south of the Primorsky krai are studied. The measured parameters are pH and the concentration of principal ions, dissolved organic carbon, silicon, and metals in the samples of precipitation and snow cover taken in Vladivostok and in the background area of the Sikhote-Alin mountain range. Data from Primorskaya, Ternei, and Sadgorod stations are presented for comparison.     

2017年5—7月内蒙古中东部地区气象干旱及环流特征分析

利用内蒙古自治区116个气象站1981—2017年5—7月逐日降水量、平均气温观测资料和逐日综合气象干旱指数(MCI)监测值。美国NCEP/NCAR 1981—2017年5—7月平均再分析资料等,分析了2017年5—7月内蒙古中东部地区发生的大范围持续气象干旱的气候背景、季风和大气环流特点等,得出:(1)2017年5—7月内蒙古中东部地区降水量异常偏少,气温异常偏高,且持续时间长,影响严重,是近36a来少有的。(2)北极涛动指数维持正位相,冷空气活动势力弱,欧亚地区盛行纬向环流;青藏高原高度场持续偏高,印缅槽持续偏弱;太平洋副热带高压强度偏强、面积偏大、西伸脊点偏西;南海夏季风较常年偏弱,我国主雨带位置偏南。大气环流的异常分布和共同影响,使得内蒙古中东部地区长时段处于高温的环流影响下,没有系统性的西南水汽输送,出现了大范围持续异常高温少雨天气,导致内蒙古中东部地区持续重旱。     

Size distribution and chemical composition of marine aerosols: a compilation and review

Some 30 years of physical and chemical marine aerosol data are reviewed to derive global‐size distribution parameters and inorganic particle composition on a coarse 15°×15° grid. There are large gaps in geographical and seasonal coverage and chemical and physical aerosol characterisation. About 28% of the grid cells contain physical data while there are compositional data in some 60% of the cells. The size distribution data were parametrized in terms of 2 submicrometer log‐normal distributions. The sparseness of the data did not allow zonal differentiation of the distributions. By segregating the chemical data according to the major aerosol sources, sea salt, dimethylsulfide, crustal material, combustion processes and other anthropogenic sources, much information on mass concentrations and contribution of natural and anthropogenic sources to the marine aerosol can be gleaned from the data base. There are significant meridional differences in the contributions of the different sources to the marine aerosol. Very clearly, we see though that the global marine surface atmosphere is polluted by anthropogenic sulfur. Only in the case of sulfur components did the coverage allow the presentation of very coarse seasonal distributions which reflect the spring blooms in the appropriate parts of the oceans. As an example of the potential value in comparing the marine aerosol data base to chemical transport models, global seasonal meridional MSA distributions were compared to modelled MSA distributions. The general good agreement in mass concentrations is encouraging while some latitudinal discrepancies warrant further investigations covering other aerosol components such as black carbon and metals.