Exhibitors—1967 APCA Annual Meeting

In recent years there has been considerable use of optical observations to determine the aerosol mass loading of the atmosphere. Nephelometer measurements of the scattering coefficient have been used for the local volume mass loading, and the turbidity of the atmosphere determined by the Volz sun photometer has been related to the vertical mass loading. This paper analyses various approaches to measuring the mass loading, and presents improved relationships between the optical observations and the aerosol mass loading.     

Signs of a negative trend in the MODIS aerosol optical depth over the Southern Balkans

A negative trend is being revealed in the MODIS aerosol optical depth [AOD] observed over the Southern Balkan/Eastern Mediterranean region. Collection 005 MODIS/Terra and MODIS/Aqua AOD at 470 nm measurements were evaluated against Brewer ground-based measurements over Thessaloniki, Greece and CIMEL ground-based measurements of AOD over Heraklion, Crete. A detailed study of the monthly, seasonal and inter-annual variability of the MODIS/Terra and MODIS/Aqua AOD values over selected locations around the Balkan Peninsula showed that the higher mean AOD values occurred in the spring and summer months, whereas the lowest were found in the winter-time. For all seasons, the highest AODs were observed for the northern-most latitudes with a marked decrease towards the southern-most sites. A statistically significant decreasing trend in aerosol load in the region over all sites as derived from the MODIS/Terra measurements gave the highest per annum change seen for the summer months to be ?4.09 ± 2.34%, and the lowest for the winter months as ?2.55 ± 4.36%, which also shows the higher variability.     

The effect of aerosol optical depth on rainfall with reference to meteorology over metro cities in India

Rainfall is a key link in the global water cycle and a proxy for changing climate; therefore, proper assessment of the urban environment’s impact on rainfall will be increasingly important in ongoing climate diagnostics and prediction. Aerosol optical depth (AOD) measurements on the monsoon seasons of the years 2008 to 2010 were made over four metro regional hotspots in India. The highest average of AOD was in the months of June and July for the four cities during 3 years and lowest was in September. Comparing the four regions, Kolkata was in the peak of aerosol contamination and Chennai was in least. Pearson correlation was made between AOD with climatic parameters. Some changes in the parameters were found during drought year. Temperature, cloud parameters, and humidity play an important role for the drought conditions. The role of aerosols, meteorological parameters, and their impacts towards the precipitation during the monsoon was studied.     

Seasonal variability of aerosol optical properties over Beijing

The knowledge of aerosol properties at local and regional scale is important in understanding of the global climate change. In this study, the aerosol optical properties over Beijing have been presented from the Aerosol Robotic Network (AERONET) measurements during 2002–2007. The aerosol optical depth (AOD) showed a distinct seasonal variation with high values in spring (March–May) and summer (June–August). The magnitude of Ångström exponent (α) was found to be relatively high throughout the year and the highest values (1.27) occurred in summer and the lowest (1.0) in spring. The water vapor retrieved from AERONET was found to be highest (2.60 cm) in summer. The fine modes of aerosol volume size distributions showed the highest peak around radius 0.15 μm in spring, autumn (September–November) and winter (December–February), and radius 0.19 μm in summer. The coarse modes showed the maxima peak at radius 3.0 μm in all seasons. The asymmetry factor (g) has considered as 0.65 at 440, 675, 870 and 1020 nm over Beijing in climate and radiation models. The average values of the single scattering albedo (SSA) at the four wavelengths were taken as 0.89, 0.91, 0.87 and 0.86 in spring, summer, autumn and winter, respectively. Both real and imaginary parts of the refractive index showed low wavelength dependence. The highest averages of real (1.52) and imaginary parts (0.0165) were found in spring and winter respectively in the wavelength range of 440–1020 nm. The aerosol properties over Beijing were found to highly dependent on season, and changes in aerosol properties were mainly attributed to the presence of dust as the main component during the spring season and the dominance of anthropogenic pollutants during the winter season.     

Impact of the mixing boundary layer on the relationship between PM2.5 and aerosol optical thickness

The purpose of this paper is to study the relationship between columnar aerosol optical thickness and ground-level aerosol mass. A set of Sun photometer, elastic backscattering lidar and TEOM measurements were acquired during April 2007 in Lille, France. The PM2.5 in the mixed boundary layer is estimated using the lidar signal, aerosol optical thickness, or columnar integrated Sun photometer size distribution and compared to the ground-level station measurements. The lidar signal recorded in the lowest level (240 m) is well correlated to the PM2.5 (R² = 0.84). We also show that the correlation between AOT-derived and measured PM2.5 is significantly improved when considering the mixed boundary layer height derived from the lidar. The use of the Sun photometer aerosol fine fraction volume does not improve the correlation.     

Shortwave radiative forcing efficiency of urban aerosols--a case study using ground based measurements

Aerosols reduce the surface reaching solar flux by scattering the incoming solar radiation out to space. Various model studies on climate change suggest that surface cooling induced by aerosol scattering is the largest source of uncertainty in predicting the future climate. In the present study measurements of aerosol optical depth (AOD) and its direct radiative forcing efficiency has been presented over a typical tropical urban environment namely Hyderabad during December, 2003. Measurements of AOD have been carried out using MICROTOPS-II sunphotometer, black carbon aerosol mass concentration using Aethalometer, total aerosol mass concentration using channel Quartz Crystal Microbalance (QCM) Impactor Particle analyser and direct normal solar irradiance using Multifilter Rotating Shadow Band Radiometer (MFRSR). Diurnal variation of AOD showed high values during afternoon hours. The fraction of BC estimated to be approximately 9% in the total aerosol mass concentration over the study area. Results of the study suggest -62.5 Wm(-2) reduction in the ground reaching shortwave flux for every 0.1 increase in aerosol optical depth. The results have been discussed in the paper.     

西安市及周边地区MODIS气溶胶光学厚度与PM10浓度关系模型研究

西安是空气污染监控和防治有代表性的西部大型城市。研究了西安市及周边地区上空气溶胶光学厚度与PM10浓度的关系模型。利用2011—2012年MODIS卫星气溶胶光学厚度（AOD）遥感产品,通过数据匹配,利用地面气象观测站点的能见度数据和相对湿度数据对AOD产品进行垂直标高订正和湿度订正,2项订正显著提高了AOD和地面PM10浓度的相关性,相关系数从0．36提高到0．65,按季节分类统计和订正春至冬四季的相关系数分别为0．57、0．71、0．62和0．87,夏季和冬季的订正更为有效,可用性更高,这可能由于受到不同季节气溶胶来源和特征的影响。为研究中国西部大型城市,特别是西安市空气环境监测和区域联防联控提供了一种有效方法。     

Aerosol composition and sources in Urban areas in India

The elemental composition of aerosols over four cities in India was determined by EDXRF over a 1-year period and the results are presented. The crustal element levels in air in all the cities are found to be similar to those reported for urban areas elsewhere in the world while that of anthropogenic elements are lower. The aerosol compositions show a seasonal variation. The levels of crustal elements are higher during summer and decrease with rainfall. The anthropogenic elements are generally higher during winter. The lead levels are essentially from non-auto exhaust sources such as refuse burning, smelter etc., and in three of the cities they are strongly correlated to zinc. The crustal elements are from local soils and no significant crust-air fractionation is seen. Factor analysis of the data suggests between four and six aerosol source types for the four cities. Soil dust accounts for the major fraction of the measured mass. About 68–80 % of the aerosol mass comprising the residuals seems to consist of C, O₂ and N, in particular, which were not measured.     

Investigations of an intense aerosol loading during 2007 cyclone SIDR – A study using satellite data and ground measurements over Indian region

Tropical cyclones are prominent weather systems characterized by high atmospheric pressure gradients and wind speeds. Intense tropical cyclones occur in India during the pre-monsoon (spring), early monsoon (early summer), or post-monsoon (fall) periods. Originating in both the Bay of Bengal (BoB) and the Arabian Sea (AS), these tropical cyclones often attain velocities of more than 100 km h^?1 and are notorious for causing intense rain and storm surge as they cross the Indian coast. In this study, we examine the changes in the aerosol properties associated with an intense tropical cyclone “SIDR”, that occurred during 11–16 November 2007 over BoB. This cyclone, accompanied with very strong surface winds reaching 223 km h^?1, caused extensive damage over Bangladesh. Ground-based measurements of Aerosol Optical Depth (AOD) in the neighboring urban environment of Hyderabad, India, showed significant variations due to changes in wind velocity and direction associated with the cyclone passage. The Terra-MODIS and AVHRR satellite images showed prevalence of dust particles mixed with emissions from anthropogenic sources and biomass-burning AS, while the aerosol loading over BoB was significantly lower. The positive values of Aerosol index (AI) obtained from the Ozone Monitoring Instrument (OMI) suggested the presence of an elevated aerosol layer over the West coast of India, AS and Thar Desert during and after the cyclone episode. Meteorological parameters from the MM5 mesoscale model were used to study the variations in winds associated with the cyclonic activity. Particulate matter loading over the region during the cyclone period increased by ～45% with an accompanying decrease in columnar aerosol optical depth. The variations in Angstrom parameters suggested coarse-mode particle loading due to dust aerosols as observed in satellite data.     

Simulation of aerosol direct radiative forcing with RAMS-CMAQ in East Asia

The air quality modeling system RAMS-CMAQ is developed to assess aerosol direct radiative forcing by linking simulated meteorological parameters and aerosol mass concentration with the aerosol optical properties/radiative transfer module in this study. The module is capable of accounting for important factors that affect aerosol optical properties and radiative effect, such as incident wave length, aerosol size distribution, water uptake, and internal mixture. Subsequently, the modeling system is applied to simulate the temporal and spatial variations in mass burden, optical properties, and direct radiative forcing of diverse aerosols, including sulfate, nitrate, ammonium, black carbon, organic carbon, dust, and sea salt over East Asia throughout 2005. Model performance is fully evaluated using various observational data, including satellite monitoring of MODIS and surface measurements of EANET (Acid Deposition Monitoring Network), AERONET (Aerosol Robotic Network), and CSHNET (Chinese Sun Hazemeter Network). The correlation coefficients of the comparisons of daily average mass concentrations of sulfate, PM2.5, and PM10 between simulations and EANET measurements are 0.70, 0.61, and 0.64, respectively. It is also determined that the modeled aerosol optical depth (AOD) is in congruence with the observed results from the AERONET, the CSHNET, and the MODIS. The model results suggest that the high AOD values ranging from 0.8 to 1.2 are mainly distributed over the Sichuan Basin as well as over central and southeastern China, in East Asia. The aerosol direct radiative forcing patterns generally followed the AOD patterns. The strongest forcing effect ranging from −12 to −8 W m⁻² was mainly distributed over the Sichuan Basin and the eastern China’s coastal regions in the all-sky case at TOA, and the forcing effect ranging from −8 to −4 W m⁻² could be found over entire eastern China, Korea, Japan, East China Sea, and the sea areas of Japan     

西安市及周边地区MODIS气溶胶光学厚度与PM10浓度关系模型研究简

西安是空气污染监控和防治有代表性的西部大型城市。研究了西安市及周边地区上空气溶胶光学厚度与PM₁₀浓度的关系模型。利用2011—2012年MODIS卫星气溶胶光学厚度（AOD）遥感产品,通过数据匹配,利用地面气象观测站点的能见度数据和相对湿度数据对AOD产品进行垂直标高订正和湿度订正,2项订正显著提高了AOD和地面PM₁₀浓度的相关性,相关系数从0.36提高到0.65,按季节分类统计和订正春至冬四季的相关系数分别为0.57、0.71、0.62和0.87,夏季和冬季的订正更为有效,可用性更高,这可能由于受到不同季节气溶胶来源和特征的影响。为研究中国西部大型城市,特别是西安市空气环境监测和区域联防联控提供了一种有效方法。     

Physical features of the atmospheric aerosol determined with an aureolemeter and a FSSP probe in the Mediterranean Lampedusa island

In order to investigate the influence of the atmospheric aerosol on the ultraviolet radiation on earth, the measurement campaign Photochemical Activity and Ultraviolet Radiation (PAUR II) Modulation was carried out in the central Mediterranean Sea during the period May–June 1999. Two sites were chosen for measurements: the island of Crete (Greece), and the island of Lampedusa (Italy). The aerosol features over the Lampedusa island, as well as the dust coming from Sahara desert, were investigated by measurements of direct and diffuse solar irradiance carried out with an aureolemeter. The columnar volume size distributions of the aerosol showed a four-modal shape in a less turbid atmosphere when the aerosol optical depth was less than 0.2 at λ=500 nm, and a tri-modal shape in a turbid atmosphere when the aerosol optical depth at the same wavelength was greater than 0.5; the background aerosol turned out to be mainly composed of sea salt. The increase of the aerosol optical depth and of the particles density with radius about 1 μm has been found to be strictly related to the passage of Saharan dust in the time periods 14–22 May and 1–3 June, 1999. The columnar volume of particles obtained by the aureolemeter has been compared with the columnar volume of particles retrieved by in situ measurements carried out with a forward scattering spectrometer probe (FSSP) aboard a light aircraft flying over the island. Although the above two techniques refer to aerosol columns of different height and operate with different resolutions, their relevant results are in good agreement, especially during days with lower aerosol content. The two volume radius distributions have been also compared and their behaviours show a satisfactory agreement, mainly for particles with radius greater than 1 μm.     

Seasonal and monthly variations of columnar aerosol optical properties over east Asia determined from multi-year MODIS,LIDAR, and AERONET Sun/sky radiometer measurements

Multi-year records of MODIS, micro-pulse lidar (MPL), and aerosol robotic network (AERONET) Sun/sky radiometer measurements were analyzed to investigate the seasonal, monthly and geographical variations of columnar aerosol optical properties over east Asia. Similar features of monthly and seasonal variations were found among the measurements, though the observational methodology and periods are not coincident. Seasonal and monthly cycles of MODIS-derived aerosol optical depth (AOD) over east Asia showed a maximum in spring and a minimum in autumn and winter. Aerosol vertical extinction profiles measured by MPL also showed elevated aerosol loads in the middle troposphere during the spring season. Seasonal and spatial distributions were related to the dust and anthropogenic emissions in spring, but modified by precipitation in July–August and regional atmospheric dispersion in September–February. All of the AERONET Sun/sky radiometers utilized in this study showed the same seasonal and monthly variations of MODIS-derived AOD. Interestingly, we found a peak of monthly mean AOD over industrialized coastal regions of China and the Yellow Sea, the Korean Peninsula, and Japan, in June from both MODIS and AERONET Sun/sky radiometer measurements. Especially, the maximum monthly mean AOD in June is more evident at the AERONET urban sites (Beijing and Gwangju). This AOD June maximum is attributable to the relative contribution of various processes such as stagnant synoptic meteorological patterns, secondary aerosol formation, hygroscopic growth of hydrophilic aerosols due to enhanced relative humidity, and smoke aerosols by regional biomass burning.     

Visibility trends in Korea during the past two decades

Temporal trends and spatial distributions of visibility measured by the human eye over 60 stations in Korea between 1980 and 2000 are analyzed and discussed. Generally, visibility is lowest on winter mornings and highest on summer afternoons throughout Korea. Visibility in Seoul is now in an increasing trend while it has decreased nationwide, especially in clean coastal areas. Spatial distribution of visibility in the 1990s was related negatively to that of relative humidity (RH). However, visibility generally decreased despite an overall decrease in RH throughout the country. Air pollutants should have played a role in this dissonant variation, particularly in relatively clean areas and on summer afternoons. It was interpreted that the visibility increase in major metropolitan areas, including the greater Seoul area, in the 1990s was caused mainly by the reduction in pollutant emissions by rigorous government policy. But the effect of the emission reduction was manifested with decreasing RH.     

Visibility Trends in Korea during the Past Two Decades

Abstract

Temporal trends and spatial distributions of visibility measured by the human eye over 60 stations in Korea between 1980 and 2000 are analyzed and discussed. Generally, visibility is lowest on winter mornings and highest on summer afternoons throughout Korea. Visibility in Seoul is now in an increasing trend while it has decreased nationwide, especially in clean coastal areas. Spatial distribution of visibility in the 1990s was related negatively to that of relative humidity (RH). However, visibility generally decreased despite an overall decrease in RH throughout the country. Air pollutants should have played a role in this dissonant variation, particularly in relatively clean areas and on summer afternoons. It was interpreted that the visibility increase in major metropolitan areas, including the greater Seoul area, in the 1990s was caused mainly by the reduction in pollutant emissions by rigorous government policy. But the effect of the emission reduction was manifested with decreasing RH.     

Impact of stratospheric volcanic aerosols on climate: Evidence for aerosol shortwave and longwave forcing in the Southeastern U.S.

Major volcanic eruptions inject massive amounts of dust and gases into the lower stratosphere and upper troposphere. Stratospheric volcanic aerosols can scatter incoming solar radiation to space, increasing planetary albedo, reducing the total amount of solar energy reaching the troposphere and the earth's surface, and decreasing the daytime maximum temperature (aerosol shortwave forcing). They can also absorb and scatter outgoing terrestrial longwave radiation, increasing the nighttime minimum surface temperature (longwave forcing). However, persuasive evidence of climate response to this forcing has thus far been lacking. Here we examine patterns of annual and seasonal variations in mean maximum and minimum temperature trend during the periods 1992–1994 and 1985–1987 relative to that during the period 1988–1990 at 47 stations in the southeastern U.S. for evidence of such climate responses. The stratospheric volcanic aerosol optical depths over the southeastern U.S. during the period 1985–1994 were inferred from the Stratospheric Aerosol and Gases Experiment (SAGE) 11 satellite extinction measurement. After the long-term trend signals are removed, it is shown that the dominant decreasing trend of mean maximum temperature and the dominant increasing trend of mean minimum temperature over periods 1992–1994 and 1985–1987 relative to that over the period 1988–1990 are consistent with the distribution of stratospheric volcanic aerosols and predictions from aerosol radiative forcing in the southeastern U.S.     

African dust contributions to mean ambient PM10 mass-levels across the Mediterranean Basin

Data on mass-levels of PM₁₀ measured at regional background sites across the Mediterranean Basin, available from Airbase (European Environmental Agency) and from a few aerosol research sites, are compiled. PM₁₀ levels increase from north to south and west to east of the Basin. These variations are roughly coincident with the PM₁₀ African mineral dust load. However, when subtracting the African dust from mean PM₁₀ levels using a consistent methodology, the PM₁₀ background levels are still 5–10 μg m^?3 higher in the Eastern Basin (EMB) when compared with those in the Western (WMB), mainly due to the higher anthropogenic and sea spray loads.As regards for the seasonal trends, these are largely driven by the occurrence of African dust events, resulting in a spring-early summer maximum over the EMB, and a clear summer maximum in the WMB, although in this later region the recirculations of aged air masses play an important role. Furthermore, a marked seasonal trend is still evident when subtracting the African dust load. This is characterised by a high summer maximum (driven by low precipitation, high insolation) and a winter minimum (intense synoptic winds).Important inter-annual variations in the dust contribution are detected, more evident in the southern sites. These differences are generally associated with the occurrence of extreme dust events. Generally, the years with higher dust contributions over the EMB correspond with lower contributions over the WMB, and vice versa.The characterization of individual particles, collected in both basins during African dust events, by scanning electron microscopy reveals only slight differences between them. This fact probably reflects the high degree of mixture of mineral dust from different sources before the transport towards the receptor sites.     

Fine particulate matter and visibility in the Lake Tahoe Basin: chemical characterization, trends, and source apportionment

Speciated PM2.5 (particulate matter with an aerodynamic diameter相似文献   

Characterization of aerosols and its radiative impacts over urban and rural environments--a case study from Hyderabad and Srisailam

In the troposphere anthropogenic aerosol emissions are increasing in recent decades, which can influence the earth's climate. The present study addresses the characterization of aerosols and their radiative impacts over urban (Hyderabad) and rural (Srisailam) environments by using aerosol optical depth (AOD) measurements from MICROTOPS-II sunphotometer. AOD measurements over the urban site showed high values compared to the rural site. Over the urban environment aerosol forcing at the surface is as high as -42 W m(-2) and at the top of the atmosphere (TOA) is +10 W m(-2) whereas at the rural environment aerosol forcing at the surface has been observed to be -11 W m(-2) and at TOA it is observed to be +5.7 W m(-2). The difference between TOA and the surface forcing over the urban environment is +32 W m(-2) and over the rural environment is +5.3 W m(-2), which shows the absorption capacity of the respective atmospheres.