The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on cli- mate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. ...The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on cli- mate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. A multi-wavelength （405 rim, 532 nm, 780 nm） aerosol absorption meter based on photoacoustic spectroscopy （PAS） invovling a single cylin- drical acoustic resonator is developed for measuring the aerosol optical absorption coefficients （OACs）. A sensitivity of 1.3 Mm-l （at 532 nm） is demonstrated. The aerosol absorption meter is successfully tested through measuring the OACs of atmospheric nigrosin and ambient aerosols in the suburbs of Hefei city. The absorption cross section and absorption Angstrom exponent （AAE） for ambient aerosol are determined for characterizing the component of the ambient aerosol.展开更多
Seasonal variation of the Tianjin coastal atmospheric aerosol opticalproperties are important for improving the atmosphere correction precision of marinesatellite and learning the environment of the boundary between t...Seasonal variation of the Tianjin coastal atmospheric aerosol opticalproperties are important for improving the atmosphere correction precision of marinesatellite and learning the environment of the boundary between the Bohai Sea and theland. In this paper, the aerosol optical data of Tianjin coastal area from April 2010 toMay 2011 were observed by using the CE317 Solar Photometer, and the aerosol opticalproperties were analyzed. The results show that: Aerosol Optical Thickness (AOT)spectra are basically in accord with Angstrom relationship; there are three basic typesof AOT daily variations, which are rising type, levelling type, and declining type; inTianjin Coastland, the mean value of AOT is highest in autumn, which is 0.686. Thevalue is lower in spring and summer, and hits the lowest point in winter. Angstromexponent α increases successively from spring, summer, autumn to winter. Due to thedusty, the angstrom exponent α in spring is lowest, the mean of which is 0.854.Compared with Qingdao Coastland, the atmospheric aerosol optical properties presentcharacteristics of regionality.展开更多
The uncertainty in the quantification of aerosol properties such as concentration, size, and composition, spatially and temporally makes regional studies important. Therefore, this study presents seasonal variations o...The uncertainty in the quantification of aerosol properties such as concentration, size, and composition, spatially and temporally makes regional studies important. Therefore, this study presents seasonal variations of aerosol optical properties over Ilorin (8䓠'N, 4䓢'E), Nigeria. Long-term (1998-2013) records of aerosol optical depth (AOD) and angstrom exponent α, from ground-based Aerosol Robotic Network (AERONET) are used to study the seasonal variability, characteristics and types of aerosol. The study showed that seasonal variations (Harmattan and Summer) result in different aerosol concentration, characteristics, and types. The magnitude and sensitivity of AOD to wavelength are found low in Summer with significant increase during Saharan dust transport season (Harmattan). The average mean AODs are 0.73 ± 0.50, 0.97 ± 0.52 and 0.46 ± 0.29 with corresponding mean angstrom of 0.66 ± 0.36, 0.68 ± 0.34, and 0.64 ± 0.37 for the entire period, Harmattan and Summer seasons. High frequency of occurrence of angstrom exponent below 1 (78% and 81%) which were observed during Harmattan and Summer indicates that the particles are generally coarse in mode. The results revealed that for both Harmattan and Summer seasons, the dominant aerosol was dust (DA) with frequency of occurrence of 82% and 79%. However, mixed aerosol (MIXA) (14.4%) is the second dominant case during Harmattan while in Summer maritime aerosol (MA) (9.1%) associated with transport due to southwesterly trade wind is the second dominant aerosol. This conclusion is supported by size distribution data for the study site which showed that large volume of aerosol particle size are enclosed in largely coarse mode range in all seasons. A 7-day back trajectory seasonal frequency plot sourced from the Hysplit Single Particles Lagrangian Integrated Trajectory model (Hysplit_4 model) shows that dust are transported from the Sahara during north-easterly trade wind flow while the observed marine aerosols are conveyed by the southwesterly trade wind influences to the study site.展开更多
Recent vigorous industrialization and urbanization in Shandong Peninsula,China,have resulted in the emission of heavy anthropogenic aerosols over the region.The annual means of aerosol optical depth(AOD),Angstrom expo...Recent vigorous industrialization and urbanization in Shandong Peninsula,China,have resulted in the emission of heavy anthropogenic aerosols over the region.The annual means of aerosol optical depth(AOD),Angstrom exponent(α),single-scattering albedo(SSA),aerosol direct radiative forcing(ARF),surface radiative forcing(SRF),and top-of-the atmospheric radiative forcing(TOA) recorded during 2004–2011 were respectively 0.67±0.19,1.25±0.24,0.93±0.03,47±9 W m-2,-61±9 W m-2,and-14±8 W m-2.The aerosol optical properties and ARF characteristics showed remarkable seasonal variations due to cycle changes in the aerosol components and dominance type.The atmosphere-surface system was cooled by ARF in all years of the study due to anthropogenic sulfate and nitrate emission and sea salt aerosols.The magnitude of TOA cooling was larger in summer(-15±17 W m-2) and autumn(-12±7 W m-2) than that in spring(-8±4 W m-2) and winter(-9±10 W m-2).展开更多
Neural network analysis based on Growing Hierarchical Self-Organizing Map (GHSOM) is used to examine Spatial-Temporal characteristics in Aerosol Optical Depth (AOD), Ångström Exponent (ÅE)...Neural network analysis based on Growing Hierarchical Self-Organizing Map (GHSOM) is used to examine Spatial-Temporal characteristics in Aerosol Optical Depth (AOD), Ångström Exponent (ÅE) and Precipitation Rate (PR) over selected East African sites from 2000 to 2014. The selected sites of study are Nairobi (1°S, 36°E), Mbita (0°S, 34°E), Mau Forest (0.0° - 0.6°S;35.1°E - 35.7°E), Malindi (2°S, 40°E), Mount Kilimanjaro (3°S, 37°E) and Kampala (0°N, 32.1°E). GHSOM analysis reveals a marked spatial variability in AOD and ÅE that is associated to changing PR, urban heat islands, diffusion, direct emission, hygroscopic growth and their scavenging from the atmosphere specific to each site. Furthermore, spatial variability in AOD, ÅE and PR is distinct since each variable corresponds to a unique level of classification. On the other hand, GHSOM algorithm efficiently discriminated by means of clustering between AOD, ÅE and PR during Long and Short rain spells and dry spell over each variable emphasizing their temporal evolution. The utilization of GHSOM therefore confirms the fact that regional aerosol characteristics are highly variable be it spatially or temporally and as well modulated by PR received over each variable.展开更多
Aerosol Optical Thickness （AOT）, water vapor content and derived Angstrom exponent acquired by a CIMEL sun photometer in Beijing are analyzed. Monthly means computed from quality-assured daily means, seasonal trends...Aerosol Optical Thickness （AOT）, water vapor content and derived Angstrom exponent acquired by a CIMEL sun photometer in Beijing are analyzed. Monthly means computed from quality-assured daily means, seasonal trends and inter-annual variations are presented and discussed. Summer has the highest seasonal average AOT at 440 nm （τa440）, Angstrom exponent （α440-870） and water vapor content with the values 0.93, 1.34 and 3.0 cm, respectively. The second highest seasonal average τa440 appears in spring with the largest variation of α440-870 and minimum α440-870 0.99 due to the impact of coarse particles. The minimum seasonal average τa440 （0.44） and water vapor content （0.4 cm） appear in winter. The annual average τa440 , α440-870 and water vapor content for about 4-year observation period are 0.70, 1.19 and 1.4 cm, respectively. All monthly average Angstrom exponents are within 0.8-1.4. which indicates aerosol in Beijing is a very complex mixture of both fine- and coarse-mode particles （from anthropogenic influence and natural mineral dust）.展开更多
The optical properties of aerosol as well as their impacting factors were investigated at a suburb site in Nanjing during autumn from 14 to 28 November 2012. More severe pollution was found together with lower visibil...The optical properties of aerosol as well as their impacting factors were investigated at a suburb site in Nanjing during autumn from 14 to 28 November 2012. More severe pollution was found together with lower visibility. The average scattering and absorption coefficients（B sca and B abs） were 375.7 ± 209.5 and 41.6 ± 18.7 Mm^（-1）, respectively. Higher ？ngstr？m absorption and scattering exponents were attributed to the presence of more aged aerosol with smaller particles. Relative humidity（RH） was a key factor affecting aerosol extinction. High RH resulted in the impairment of visibility, with hygroscopic growth being independent of the dry extinction coefficient. The hygroscopic growth factor was 1.8 ± 1.2 with RH from 19% to 85%.Light absorption was enhanced by organic carbon（OC）, elemental carbon（EC） and EC coatings,with contributions of 26%, 44% and 75%（532 nm）, respectively. The B sca and B abs increased with increasing N_（100）（number concentration of PM_（2.5）with diameter above 100 nm）, PM_1 surface concentration and PM_（2.5）mass concentration with good correlation.展开更多
This work aims to analyze the spatial and temporal variability of aerosol optical depth （AOD） from 2000 to 2012 in the Changjiang River Delta （CRD）, China. US Terra satellite moderate resolution imaging spectrorad...This work aims to analyze the spatial and temporal variability of aerosol optical depth （AOD） from 2000 to 2012 in the Changjiang River Delta （CRD）, China. US Terra satellite moderate resolution imaging spectroradiometer （MODIS） AOD and Angstrom exponent （a） data constitute a baseline, with the empirical orthogonal functions （EOFs） method used as a major data analysis method. The results show that the maximum value of AOD observed in June is 1.00±0.12, and the lowest value detected in December is 0.40±0.05. AOD in spring and summer is higher than in autumn and winter. On the other hand, the a-value is lowest in spring （0.86±0.10）, which are affected by coarse particles. High a-value appears in summer （1.32±0.05）, which indicate that aerosols are dominated by fine particles. The spatial distribution of AOD has a close relationship with terrain and population density. Generally, high AODs are distributed in the lowlying plains, and low AODs in the mountainous areas. The spatial and temporal patterns of seasonal AODs show that the first three EOF modes cumulatively account for 77% of the total variance. The first mode that explains 67% of the total variance shows the primary spatial distribution of aerosols, i.e., high AODs are distributed in the northern areas and low AODs in the southern areas. The second mode （7%） shows that the monsoon climate probably plays an important role in modifying the distribution of aerosols, especially in summer and winter. In the third mode （3%）, this distribution of aerosols usually occurs in spring and winter when the prevailing northwestern or western winds could bring aerosol particles from the inland areas into thecentral regions of the CRD.展开更多
基金supported by the Open Research Fund of Key Laboratory of Atmospheric Composition and Optical Radiation,Chinese Academy of Sciencesthe National Natural Science Foundation of China(Grant Nos.41175036 and 41205120)
文摘The atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on cli- mate. Accurate measurement is highly desired for the study of the radiative budget of the Earth. A multi-wavelength （405 rim, 532 nm, 780 nm） aerosol absorption meter based on photoacoustic spectroscopy （PAS） invovling a single cylin- drical acoustic resonator is developed for measuring the aerosol optical absorption coefficients （OACs）. A sensitivity of 1.3 Mm-l （at 532 nm） is demonstrated. The aerosol absorption meter is successfully tested through measuring the OACs of atmospheric nigrosin and ambient aerosols in the suburbs of Hefei city. The absorption cross section and absorption Angstrom exponent （AAE） for ambient aerosol are determined for characterizing the component of the ambient aerosol.
基金supported by Science Foundation for The Excellent Youth Scholars of Tianjin
文摘Seasonal variation of the Tianjin coastal atmospheric aerosol opticalproperties are important for improving the atmosphere correction precision of marinesatellite and learning the environment of the boundary between the Bohai Sea and theland. In this paper, the aerosol optical data of Tianjin coastal area from April 2010 toMay 2011 were observed by using the CE317 Solar Photometer, and the aerosol opticalproperties were analyzed. The results show that: Aerosol Optical Thickness (AOT)spectra are basically in accord with Angstrom relationship; there are three basic typesof AOT daily variations, which are rising type, levelling type, and declining type; inTianjin Coastland, the mean value of AOT is highest in autumn, which is 0.686. Thevalue is lower in spring and summer, and hits the lowest point in winter. Angstromexponent α increases successively from spring, summer, autumn to winter. Due to thedusty, the angstrom exponent α in spring is lowest, the mean of which is 0.854.Compared with Qingdao Coastland, the atmospheric aerosol optical properties presentcharacteristics of regionality.
文摘The uncertainty in the quantification of aerosol properties such as concentration, size, and composition, spatially and temporally makes regional studies important. Therefore, this study presents seasonal variations of aerosol optical properties over Ilorin (8䓠'N, 4䓢'E), Nigeria. Long-term (1998-2013) records of aerosol optical depth (AOD) and angstrom exponent α, from ground-based Aerosol Robotic Network (AERONET) are used to study the seasonal variability, characteristics and types of aerosol. The study showed that seasonal variations (Harmattan and Summer) result in different aerosol concentration, characteristics, and types. The magnitude and sensitivity of AOD to wavelength are found low in Summer with significant increase during Saharan dust transport season (Harmattan). The average mean AODs are 0.73 ± 0.50, 0.97 ± 0.52 and 0.46 ± 0.29 with corresponding mean angstrom of 0.66 ± 0.36, 0.68 ± 0.34, and 0.64 ± 0.37 for the entire period, Harmattan and Summer seasons. High frequency of occurrence of angstrom exponent below 1 (78% and 81%) which were observed during Harmattan and Summer indicates that the particles are generally coarse in mode. The results revealed that for both Harmattan and Summer seasons, the dominant aerosol was dust (DA) with frequency of occurrence of 82% and 79%. However, mixed aerosol (MIXA) (14.4%) is the second dominant case during Harmattan while in Summer maritime aerosol (MA) (9.1%) associated with transport due to southwesterly trade wind is the second dominant aerosol. This conclusion is supported by size distribution data for the study site which showed that large volume of aerosol particle size are enclosed in largely coarse mode range in all seasons. A 7-day back trajectory seasonal frequency plot sourced from the Hysplit Single Particles Lagrangian Integrated Trajectory model (Hysplit_4 model) shows that dust are transported from the Sahara during north-easterly trade wind flow while the observed marine aerosols are conveyed by the southwesterly trade wind influences to the study site.
基金supported by the National Natural Science Foundation of China(41222033,41375036,and 41105103)and the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA05100102 and XDB05020103)
文摘Recent vigorous industrialization and urbanization in Shandong Peninsula,China,have resulted in the emission of heavy anthropogenic aerosols over the region.The annual means of aerosol optical depth(AOD),Angstrom exponent(α),single-scattering albedo(SSA),aerosol direct radiative forcing(ARF),surface radiative forcing(SRF),and top-of-the atmospheric radiative forcing(TOA) recorded during 2004–2011 were respectively 0.67±0.19,1.25±0.24,0.93±0.03,47±9 W m-2,-61±9 W m-2,and-14±8 W m-2.The aerosol optical properties and ARF characteristics showed remarkable seasonal variations due to cycle changes in the aerosol components and dominance type.The atmosphere-surface system was cooled by ARF in all years of the study due to anthropogenic sulfate and nitrate emission and sea salt aerosols.The magnitude of TOA cooling was larger in summer(-15±17 W m-2) and autumn(-12±7 W m-2) than that in spring(-8±4 W m-2) and winter(-9±10 W m-2).
基金This work was supported by the National Council for Science and Technology Grant funded by the Government of Kenya(NCST/ST&I/RCD/4TH call PhD/201).
文摘Neural network analysis based on Growing Hierarchical Self-Organizing Map (GHSOM) is used to examine Spatial-Temporal characteristics in Aerosol Optical Depth (AOD), Ångström Exponent (ÅE) and Precipitation Rate (PR) over selected East African sites from 2000 to 2014. The selected sites of study are Nairobi (1°S, 36°E), Mbita (0°S, 34°E), Mau Forest (0.0° - 0.6°S;35.1°E - 35.7°E), Malindi (2°S, 40°E), Mount Kilimanjaro (3°S, 37°E) and Kampala (0°N, 32.1°E). GHSOM analysis reveals a marked spatial variability in AOD and ÅE that is associated to changing PR, urban heat islands, diffusion, direct emission, hygroscopic growth and their scavenging from the atmosphere specific to each site. Furthermore, spatial variability in AOD, ÅE and PR is distinct since each variable corresponds to a unique level of classification. On the other hand, GHSOM algorithm efficiently discriminated by means of clustering between AOD, ÅE and PR during Long and Short rain spells and dry spell over each variable emphasizing their temporal evolution. The utilization of GHSOM therefore confirms the fact that regional aerosol characteristics are highly variable be it spatially or temporally and as well modulated by PR received over each variable.
基金This research is supported by a China-France PRA project, the National Science Foundation of China （40250120071）the Chinese Academy of Sciences （2003-2-9）
文摘Aerosol Optical Thickness （AOT）, water vapor content and derived Angstrom exponent acquired by a CIMEL sun photometer in Beijing are analyzed. Monthly means computed from quality-assured daily means, seasonal trends and inter-annual variations are presented and discussed. Summer has the highest seasonal average AOT at 440 nm （τa440）, Angstrom exponent （α440-870） and water vapor content with the values 0.93, 1.34 and 3.0 cm, respectively. The second highest seasonal average τa440 appears in spring with the largest variation of α440-870 and minimum α440-870 0.99 due to the impact of coarse particles. The minimum seasonal average τa440 （0.44） and water vapor content （0.4 cm） appear in winter. The annual average τa440 , α440-870 and water vapor content for about 4-year observation period are 0.70, 1.19 and 1.4 cm, respectively. All monthly average Angstrom exponents are within 0.8-1.4. which indicates aerosol in Beijing is a very complex mixture of both fine- and coarse-mode particles （from anthropogenic influence and natural mineral dust）.
基金supported by the Commonwealth Program of Environment Protection Department of China (No.201409027-05)the National Natural Science Foundation of China (No.21577065)+2 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Postgraduate Innovation Foundation of Jiangsu Province (No.CXZZ11_0611)the International ST Cooperation Program of China (ISTCP) (No.2014DFA90780)
文摘The optical properties of aerosol as well as their impacting factors were investigated at a suburb site in Nanjing during autumn from 14 to 28 November 2012. More severe pollution was found together with lower visibility. The average scattering and absorption coefficients（B sca and B abs） were 375.7 ± 209.5 and 41.6 ± 18.7 Mm^（-1）, respectively. Higher ？ngstr？m absorption and scattering exponents were attributed to the presence of more aged aerosol with smaller particles. Relative humidity（RH） was a key factor affecting aerosol extinction. High RH resulted in the impairment of visibility, with hygroscopic growth being independent of the dry extinction coefficient. The hygroscopic growth factor was 1.8 ± 1.2 with RH from 19% to 85%.Light absorption was enhanced by organic carbon（OC）, elemental carbon（EC） and EC coatings,with contributions of 26%, 44% and 75%（532 nm）, respectively. The B sca and B abs increased with increasing N_（100）（number concentration of PM_（2.5）with diameter above 100 nm）, PM_1 surface concentration and PM_（2.5）mass concentration with good correlation.
文摘This work aims to analyze the spatial and temporal variability of aerosol optical depth （AOD） from 2000 to 2012 in the Changjiang River Delta （CRD）, China. US Terra satellite moderate resolution imaging spectroradiometer （MODIS） AOD and Angstrom exponent （a） data constitute a baseline, with the empirical orthogonal functions （EOFs） method used as a major data analysis method. The results show that the maximum value of AOD observed in June is 1.00±0.12, and the lowest value detected in December is 0.40±0.05. AOD in spring and summer is higher than in autumn and winter. On the other hand, the a-value is lowest in spring （0.86±0.10）, which are affected by coarse particles. High a-value appears in summer （1.32±0.05）, which indicate that aerosols are dominated by fine particles. The spatial distribution of AOD has a close relationship with terrain and population density. Generally, high AODs are distributed in the lowlying plains, and low AODs in the mountainous areas. The spatial and temporal patterns of seasonal AODs show that the first three EOF modes cumulatively account for 77% of the total variance. The first mode that explains 67% of the total variance shows the primary spatial distribution of aerosols, i.e., high AODs are distributed in the northern areas and low AODs in the southern areas. The second mode （7%） shows that the monsoon climate probably plays an important role in modifying the distribution of aerosols, especially in summer and winter. In the third mode （3%）, this distribution of aerosols usually occurs in spring and winter when the prevailing northwestern or western winds could bring aerosol particles from the inland areas into thecentral regions of the CRD.
