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Effect of Meteorological Factors on PM2.5 during July to September of Beijing
Available online at www.sciencedirect.com
Procedia Earth and Planetary Science 2 (2011) 272 – 277
The Second International Conference on Mining Engineering and Metallurgical Technology
Effect of Meteorological Factors on PM2.5 during July to September of Beijing PU Wei-wei, ZHAO Xiu-juan, ZHANG Xiao-ling, MA Zhi-Qiang Institute of Urban Meteorology,China Meteorological Administration,Beijing 100089,China
Abstract
In order to investigate the effect of meteorological factors on PM2.5 in Beijing, the continuous observation data which from July to September of 2006-2008 of Baolian and Shangdianzi stations are used to analyze. The result showed that: the transportation of southerly wind aggravated the fine particulate pollution degree of urban, and it is also the primary reason of the pollution in rural area. PM2.5 concentration decreased as the northerly wind increased in both urban and rural areas. This indicates that the northerly wind is relatively clear, can dilute and disperses the pollutants in the Beijing area, but the southerly wind play the opposite role. Hourly precipitation above 1 mm can eliminate PM2.5 effetely. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering Keywords: PM2.5;wind direction; wind speed; precipitation
Introduction Particulate matter, one of the major air pollutants in most cities in China, has become the dominant pollutant in Beijing [1]. PM2.5 is relatively small size of Particulate matter. As fine particles, PM2.5 is most harmful to human health and hazardous to the environment [2, 3]. Moreover, PM2.5 can considerably reduce atmospheric visibility [4, 5]. Thus, research on this type of particulate matter has received increasing attention. In Beijing, the area allocated for buildings has been increasing annually since the 1990s. By the end of 2009, vehicle ownership has risen to approximately 4 million; as a result, motor vehicle emissions have become a major source of PM2.5 in Beijing [6]. In this study, the mass concentration of PM2.5 has been measured continuously at an urban site and a rural site in Beijing for
1878–5220 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeps.2011.09.043
273
PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
three years (2006—2008). Using these observations, we analyze the characteristics of particulate matter in Beijing before and after the Olympic Games.
1. Materials and methods PM2.5 concentrations are monitored at Baolian (urban station, 39q56cN, 116q17cE, 75.0 m) and the Shangdianzi regional atmospheric background station (rural station, 40q39cN, 117q07cE, 293.9 m). Both stations use a TEOM 1400a (R&P Company) to monitor PM2.5 concentrations. The filter loading percentage and flow rates of TEOM are checked once a week, and the filter is replaced when the filter loading percentage is greater than 30%.
2. Influence of wind direction on PM2.5 concentration in the Beijing area Previous studies [7] show exchange of atmospheric pollutants between Beijing and surrounding areas. The main factors that affect the amount of pollutant transport and dispersion are wind direction and speed. To further discuss the effect of wind on the spread and transmission of pollutants in the Baolian and Shangdianzi areas, we choose the 1500 m altitude wind for statistical analysis. The terrain in Beijing is special, whose ground wind is vulnerable to the local valley wind circulation [8]. The altitude chosen is located at the top of the boundary layer, and can effectively indicate the changes in weather systems. The present study excludes the days of precipitation and uses July to September 2006–2008 sounding data (08:00 and 20:00 h daily) from the Nanjiao observatory of Beijing. The PM2.5 concentrations values during the corresponding periods are taken into analyze. Figure 1 describes the influence of wind direction on the concentration of PM2.5 at Baolian and Shangdianzi stations.
80 100
(b)
(a)
70
3
PM2.5(ȝg/m )
60
3
PM2.5(ȝg/m )
80
60
50
40
40
30
20
0
45
90
135
180
225
wind direction (deg)
270
315
20 0
45
90
135
180
225
270
315
wind direction (deg)
Fig.1 The influence of wind direction on the concentration of PM2.5 at Baolian (a) and Shangdianzi (b) stations
The comparison of the PM2.5 concentrations at different wind directions and a 1500 m altitude shows that there were high concentrations of PM2.5 at the southwest and south wind directions, reaching 98.6 and 90.1ȝg/m3, respectively. These are followed by the east, southeast, and west wind directions.
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PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
Concentrations at the remaining directions were low. The concentration at the north wind direction was lowest (52.5 ȝg/m3). Thus, when wind from the 1500 m altitude comes from the E-W direction, the city is vulnerable to particulate pollution. Wind direction can be ascertained by statistical frequency, and our analysis reveals that the frequency of the southwest wind was 26.6%, which corresponds to the highest level of particulate pollution among the eight wind directions. The frequency of the south wind was 12.1%; adding this to the frequency of the southwest wind makes up 40% of the total. Figure 2 also shows that at different wind directions, the PM2.5 concentrations of Shangdianzi station were similar to that of the Baolian station. The highest average concentration was observed at the southwest wind direction (74.1ȝg/m3) and the lowest at the north wind direction (26.6ȝg/m3). On the basis of wind direction frequency, it determine that the southwest direction had the highest frequency (25.6%), followed by the south direction (13.7%). Southerly wind that prevailed over Beijing from July to September transported the pollutants that were generated from the south of Tianjin, the southern part of Hebei Province, and some cities in Shanxi Province to Beijing. Furthermore, the blocking effect of the northern mountainous area aided the accumulation of pollutants in the Beijing area, and facilitated particulate pollution. The pollutants transported by the southerly wind not only exacerbated pollution from fine particulate matter, but also caused the emergence of fine particulate pollutants in the surrounding regional areas.
3. Influence of wind speed on PM2.5 concentration in the Beijing area Obvious differences in the concentrations of fine particulates with wind directions were observed as well. Wind direction determines the transport direction of pollutants, and wind speed determines the degree of pollutant dilution and dispersion. To analyze the effect of wind speed on PM2.5 concentration, we examine the changes in classification statistics for the wind speed of the southerly (90°0.05). These results may be attributed to the local pollution sources in urban areas, which also play an important role along with external pollutants. The actual pollutant concentration is the integrated effect of external and local sources, resulting in imperceptible relationship between the southerly wind speed and PM2.5 concentration. Figure 2 also shows that the PM2.5 concentration decreased as the northerly wind increased (p<0.05) in both urban and rural areas. This indicates that the northerly wind is relatively clear, can dilute and disperses the pollutants in the Beijing area.
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PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
200
160
Southerly wind
Northerly wind
140
160
120
140
100
PM2.5(ȝg/m ˅
120
3
3
PM2.5(ȝg/m )
180
100 80
80 60 40 20
60
0
40
(a)
20 0
2
4
6
8
(b)
-20
10
0
2
4
wind 亢䗳speed ˄m/s (m/s) ˅ 140
6
8
10
12
m/s˅(m/s) 亢 䗳 ˄speed wind
Southerly wind
Northerly wind
80
120
60 3
PM2.5(ȝg/m )
80
3
PM2.5(ȝg/m )
100
60 40
40
20
20 0
0
(c)
-20 0
2
4
6
8
10
(d) 0
wind speed (m/s) ˅ 亢䗳 ˄m/s
2
4
6
8
10
12
˅ 亢䗳 ˄m/s wind speed (m/s)
Fig.2 The influence of wind speed on the concentration of PM2.5 at Baolian (a, b) and Shangdianzi(c, d) stations
4. Effects of precipitation on PM2.5 concentration Precipitation plays a role in cleaning and washing pollutants out of air through the clear or wet deposition process. Thus, it is an important factor in maintaining the atmospheric composition. Eighty percent of the annual precipitation in Beijing is observed during the flood season (June to September) [9]. The wet deposition of atmospheric pollutants caused by precipitation is the primary means by which pollutants are removed. The role that wet deposition plays in relation to the concentration of pollutants cannot be disregarded. Therefore, analyzing the effect of precipitation on PM2.5 concentration from July to September is necessary. Table 1 presents classified statistics of the increase in PM2.5 concentration in 160 hours after precipitation in the Shangdianzi station. Precipitation was distributed widely, as proven by the distribution of hourly precipitation. However, most were concentrated in value less than 1 mm. Hourly precipitations above 1 mm accounted for only approximately 20% of the total. When the PM2.5 concentration increased, the corresponding precipitation was, in most cases, less than 1 mm. The sample size accounts for 81.3% of the total sample size. The samples whose hourly rainfall amount is less than
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PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
0.5 mm account for 66.3% of the total. This means that low rainfall amount only slightly clears particulates. With the increase in humidity however, the PM2.5 concentration increased. In addition, the initial pollutant concentration had a direct influence on the removal amount. The variations in the initial PM2.5 concentration show that at an hourly precipitation of less than 2 mm, the scope of the changes in initial concentration was relatively large. At an hourly precipitation of above 2 mm, the initial PM2.5 concentration was relatively low (the initial concentration of 100.25 ȝg/m3 occurred only once; most concentration levels were less than 30.0 ȝg/m3). In this particular situation, there were fewer particles in the atmosphere, the capture rate of precipitation was relatively low, and the changes in concentration are not obvious. In cases where fine particle concentration or precipitation volume was low, precipitation scavenging was relatively weak. The analysis in Figure 3 shows that most precipitation with no elimination effect was below 1 mm. The present study defines hourly precipitation above 1 mm as effective precipitation.
Table1 Graduation statistics of the increase of PM2.5 concentration after precipitation at Shangdianzi station
Hourly precipitation ˄mm˅
Sample size
The range of initial concentration of PM2.5˄ȝg/m3˅
The average of initial concentration of PM2.5˄ȝg/m3˅
<=0.5
106
1.5—156.33
35.8
66.3
0.5—1
24
2.64—105.17
26.4
15.0
1—2
13
1.5—108
27.9
8.1
2—3
5
7—17.4
13.3
3.1
3—4
4
9.5—100.25
47.3
2.5
4—5
3
6.33—14.08
11.2
1.9
>5
5
11.58—33.75
18.5
3.1
Ratio ˄%˅
5. Conclusions Effect of meteorological factors on PM2.5 in Beijing during July to September is analyzed. The following conclusions are drawn. The pollutants transported by the southerly wind not only increased fine particulate pollution in urban area, but also contributed to fine particulate pollution in the rural area. Meanwhile, the urban pollution source played a key role in Beijing; the actual concentration of pollutants in urban areas is the combined result of external sources and local sources. PM2.5 concentration decreased as the northerly wind increased in both urban and rural areas. This indicates that the northerly wind is relatively clear, can dilute and disperses the pollutants in the Beijing area. When the hourly precipitation reached more than 1 mm, the fine particles removed from the atmosphere effectively.
PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
Acknowledgment This research was supported by Beijing Natural Science Foundation(8092010)and Special Fund for Meteorological Research in the Public Interest(GYHY200806027)
Reference [1] Yu Shuqiu, Xu Xiangde, Lin Xuechun. Temporal and Spatial Characteristics of Air Pollution in Beijing. Journal of Applied Meteorological Science, 2002, 13(Special issue):92~99. (in Chinese) [2]Pope C.A., Burnett R., M.J, T., et al. Lung Cancer, Cardiopulmonary Mortality, and Long-term Exposure to Fine Particulate Air Pollution. Journal of the American Medical Association, 2002, 287(9):1132~1141. [3]Chan Y.C., Simpson R.W., Mctainsh G.H., et al. Source Apportionment of Visibility Degradation Problems Brisbane (Australia) Using Multiple Linear Regression Techniques. Atmospheric Environment, 1999, 33 (19): 3237~3250. [4]Yu Fenglian, Liu Dongxian, Hu Ying. The Effect of Aerosol on Visibility of City. Meteorological Science and Technology, 2002, 30(6):379 ~383. (in Chinese) [5]Song Yu, Tang Xiaoyan, Fang Chen, et al. Relationship between the Visibility Degradation and Particle Pollution in Beijing. Acta Scientiae Circumstantiae, 2003, 468~471. (in Chinese) [6]Yu Song, Xiaoyan Tang, Shaodong Xie, et al. Source apportionment of PM2.5 in Beijing in 2004. Journal of Hazardous Materials, 2007,146 (1-2):124~130. (in Chinese) [7]Ren Zhenhai, Huang Meiyuan, Dong Baoqun, et al. Studies on Transport of Acid Substance in China. Beijing, China, 1995. (in Chinese) [8] Zhao Xiujuan, Zhang Xiaoling, Xu Xiaofeng et al. Seasonal and diurnal variations of ambient PM2.5 concentration in urban and rural environments in Beijing . Atmospheric Environment, 2009, 43(18): 2893~2900. [9]Sun Zhenhua, Feng Shaoyuan, Yang Zhongshan, et al. Primary Analysis of the Precipitation Characteristics for Beijing during the Period from 1950 to 2005. Journal of Irrigation and Drainage, 2007, 26(2):12~16. (in Chinese)
277
Procedia Earth and Planetary Science 2 (2011) 272 – 277
The Second International Conference on Mining Engineering and Metallurgical Technology
Effect of Meteorological Factors on PM2.5 during July to September of Beijing PU Wei-wei, ZHAO Xiu-juan, ZHANG Xiao-ling, MA Zhi-Qiang Institute of Urban Meteorology,China Meteorological Administration,Beijing 100089,China
Abstract
In order to investigate the effect of meteorological factors on PM2.5 in Beijing, the continuous observation data which from July to September of 2006-2008 of Baolian and Shangdianzi stations are used to analyze. The result showed that: the transportation of southerly wind aggravated the fine particulate pollution degree of urban, and it is also the primary reason of the pollution in rural area. PM2.5 concentration decreased as the northerly wind increased in both urban and rural areas. This indicates that the northerly wind is relatively clear, can dilute and disperses the pollutants in the Beijing area, but the southerly wind play the opposite role. Hourly precipitation above 1 mm can eliminate PM2.5 effetely. © 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Society for Resources, Environment and Engineering Keywords: PM2.5;wind direction; wind speed; precipitation
Introduction Particulate matter, one of the major air pollutants in most cities in China, has become the dominant pollutant in Beijing [1]. PM2.5 is relatively small size of Particulate matter. As fine particles, PM2.5 is most harmful to human health and hazardous to the environment [2, 3]. Moreover, PM2.5 can considerably reduce atmospheric visibility [4, 5]. Thus, research on this type of particulate matter has received increasing attention. In Beijing, the area allocated for buildings has been increasing annually since the 1990s. By the end of 2009, vehicle ownership has risen to approximately 4 million; as a result, motor vehicle emissions have become a major source of PM2.5 in Beijing [6]. In this study, the mass concentration of PM2.5 has been measured continuously at an urban site and a rural site in Beijing for
1878–5220 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeps.2011.09.043
273
PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
three years (2006—2008). Using these observations, we analyze the characteristics of particulate matter in Beijing before and after the Olympic Games.
1. Materials and methods PM2.5 concentrations are monitored at Baolian (urban station, 39q56cN, 116q17cE, 75.0 m) and the Shangdianzi regional atmospheric background station (rural station, 40q39cN, 117q07cE, 293.9 m). Both stations use a TEOM 1400a (R&P Company) to monitor PM2.5 concentrations. The filter loading percentage and flow rates of TEOM are checked once a week, and the filter is replaced when the filter loading percentage is greater than 30%.
2. Influence of wind direction on PM2.5 concentration in the Beijing area Previous studies [7] show exchange of atmospheric pollutants between Beijing and surrounding areas. The main factors that affect the amount of pollutant transport and dispersion are wind direction and speed. To further discuss the effect of wind on the spread and transmission of pollutants in the Baolian and Shangdianzi areas, we choose the 1500 m altitude wind for statistical analysis. The terrain in Beijing is special, whose ground wind is vulnerable to the local valley wind circulation [8]. The altitude chosen is located at the top of the boundary layer, and can effectively indicate the changes in weather systems. The present study excludes the days of precipitation and uses July to September 2006–2008 sounding data (08:00 and 20:00 h daily) from the Nanjiao observatory of Beijing. The PM2.5 concentrations values during the corresponding periods are taken into analyze. Figure 1 describes the influence of wind direction on the concentration of PM2.5 at Baolian and Shangdianzi stations.
80 100
(b)
(a)
70
3
PM2.5(ȝg/m )
60
3
PM2.5(ȝg/m )
80
60
50
40
40
30
20
0
45
90
135
180
225
wind direction (deg)
270
315
20 0
45
90
135
180
225
270
315
wind direction (deg)
Fig.1 The influence of wind direction on the concentration of PM2.5 at Baolian (a) and Shangdianzi (b) stations
The comparison of the PM2.5 concentrations at different wind directions and a 1500 m altitude shows that there were high concentrations of PM2.5 at the southwest and south wind directions, reaching 98.6 and 90.1ȝg/m3, respectively. These are followed by the east, southeast, and west wind directions.
274
PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
Concentrations at the remaining directions were low. The concentration at the north wind direction was lowest (52.5 ȝg/m3). Thus, when wind from the 1500 m altitude comes from the E-W direction, the city is vulnerable to particulate pollution. Wind direction can be ascertained by statistical frequency, and our analysis reveals that the frequency of the southwest wind was 26.6%, which corresponds to the highest level of particulate pollution among the eight wind directions. The frequency of the south wind was 12.1%; adding this to the frequency of the southwest wind makes up 40% of the total. Figure 2 also shows that at different wind directions, the PM2.5 concentrations of Shangdianzi station were similar to that of the Baolian station. The highest average concentration was observed at the southwest wind direction (74.1ȝg/m3) and the lowest at the north wind direction (26.6ȝg/m3). On the basis of wind direction frequency, it determine that the southwest direction had the highest frequency (25.6%), followed by the south direction (13.7%). Southerly wind that prevailed over Beijing from July to September transported the pollutants that were generated from the south of Tianjin, the southern part of Hebei Province, and some cities in Shanxi Province to Beijing. Furthermore, the blocking effect of the northern mountainous area aided the accumulation of pollutants in the Beijing area, and facilitated particulate pollution. The pollutants transported by the southerly wind not only exacerbated pollution from fine particulate matter, but also caused the emergence of fine particulate pollutants in the surrounding regional areas.
3. Influence of wind speed on PM2.5 concentration in the Beijing area Obvious differences in the concentrations of fine particulates with wind directions were observed as well. Wind direction determines the transport direction of pollutants, and wind speed determines the degree of pollutant dilution and dispersion. To analyze the effect of wind speed on PM2.5 concentration, we examine the changes in classification statistics for the wind speed of the southerly (90°
275
PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
200
160
Southerly wind
Northerly wind
140
160
120
140
100
PM2.5(ȝg/m ˅
120
3
3
PM2.5(ȝg/m )
180
100 80
80 60 40 20
60
0
40
(a)
20 0
2
4
6
8
(b)
-20
10
0
2
4
wind 亢䗳speed ˄m/s (m/s) ˅ 140
6
8
10
12
m/s˅(m/s) 亢 䗳 ˄speed wind
Southerly wind
Northerly wind
80
120
60 3
PM2.5(ȝg/m )
80
3
PM2.5(ȝg/m )
100
60 40
40
20
20 0
0
(c)
-20 0
2
4
6
8
10
(d) 0
wind speed (m/s) ˅ 亢䗳 ˄m/s
2
4
6
8
10
12
˅ 亢䗳 ˄m/s wind speed (m/s)
Fig.2 The influence of wind speed on the concentration of PM2.5 at Baolian (a, b) and Shangdianzi(c, d) stations
4. Effects of precipitation on PM2.5 concentration Precipitation plays a role in cleaning and washing pollutants out of air through the clear or wet deposition process. Thus, it is an important factor in maintaining the atmospheric composition. Eighty percent of the annual precipitation in Beijing is observed during the flood season (June to September) [9]. The wet deposition of atmospheric pollutants caused by precipitation is the primary means by which pollutants are removed. The role that wet deposition plays in relation to the concentration of pollutants cannot be disregarded. Therefore, analyzing the effect of precipitation on PM2.5 concentration from July to September is necessary. Table 1 presents classified statistics of the increase in PM2.5 concentration in 160 hours after precipitation in the Shangdianzi station. Precipitation was distributed widely, as proven by the distribution of hourly precipitation. However, most were concentrated in value less than 1 mm. Hourly precipitations above 1 mm accounted for only approximately 20% of the total. When the PM2.5 concentration increased, the corresponding precipitation was, in most cases, less than 1 mm. The sample size accounts for 81.3% of the total sample size. The samples whose hourly rainfall amount is less than
276
PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
0.5 mm account for 66.3% of the total. This means that low rainfall amount only slightly clears particulates. With the increase in humidity however, the PM2.5 concentration increased. In addition, the initial pollutant concentration had a direct influence on the removal amount. The variations in the initial PM2.5 concentration show that at an hourly precipitation of less than 2 mm, the scope of the changes in initial concentration was relatively large. At an hourly precipitation of above 2 mm, the initial PM2.5 concentration was relatively low (the initial concentration of 100.25 ȝg/m3 occurred only once; most concentration levels were less than 30.0 ȝg/m3). In this particular situation, there were fewer particles in the atmosphere, the capture rate of precipitation was relatively low, and the changes in concentration are not obvious. In cases where fine particle concentration or precipitation volume was low, precipitation scavenging was relatively weak. The analysis in Figure 3 shows that most precipitation with no elimination effect was below 1 mm. The present study defines hourly precipitation above 1 mm as effective precipitation.
Table1 Graduation statistics of the increase of PM2.5 concentration after precipitation at Shangdianzi station
Hourly precipitation ˄mm˅
Sample size
The range of initial concentration of PM2.5˄ȝg/m3˅
The average of initial concentration of PM2.5˄ȝg/m3˅
<=0.5
106
1.5—156.33
35.8
66.3
0.5—1
24
2.64—105.17
26.4
15.0
1—2
13
1.5—108
27.9
8.1
2—3
5
7—17.4
13.3
3.1
3—4
4
9.5—100.25
47.3
2.5
4—5
3
6.33—14.08
11.2
1.9
>5
5
11.58—33.75
18.5
3.1
Ratio ˄%˅
5. Conclusions Effect of meteorological factors on PM2.5 in Beijing during July to September is analyzed. The following conclusions are drawn. The pollutants transported by the southerly wind not only increased fine particulate pollution in urban area, but also contributed to fine particulate pollution in the rural area. Meanwhile, the urban pollution source played a key role in Beijing; the actual concentration of pollutants in urban areas is the combined result of external sources and local sources. PM2.5 concentration decreased as the northerly wind increased in both urban and rural areas. This indicates that the northerly wind is relatively clear, can dilute and disperses the pollutants in the Beijing area. When the hourly precipitation reached more than 1 mm, the fine particles removed from the atmosphere effectively.
PU Wei-wei et al. / Procedia Earth and Planetary Science 2 (2011) 272 – 277
Acknowledgment This research was supported by Beijing Natural Science Foundation(8092010)and Special Fund for Meteorological Research in the Public Interest(GYHY200806027)
Reference [1] Yu Shuqiu, Xu Xiangde, Lin Xuechun. Temporal and Spatial Characteristics of Air Pollution in Beijing. Journal of Applied Meteorological Science, 2002, 13(Special issue):92~99. (in Chinese) [2]Pope C.A., Burnett R., M.J, T., et al. Lung Cancer, Cardiopulmonary Mortality, and Long-term Exposure to Fine Particulate Air Pollution. Journal of the American Medical Association, 2002, 287(9):1132~1141. [3]Chan Y.C., Simpson R.W., Mctainsh G.H., et al. Source Apportionment of Visibility Degradation Problems Brisbane (Australia) Using Multiple Linear Regression Techniques. Atmospheric Environment, 1999, 33 (19): 3237~3250. [4]Yu Fenglian, Liu Dongxian, Hu Ying. The Effect of Aerosol on Visibility of City. Meteorological Science and Technology, 2002, 30(6):379 ~383. (in Chinese) [5]Song Yu, Tang Xiaoyan, Fang Chen, et al. Relationship between the Visibility Degradation and Particle Pollution in Beijing. Acta Scientiae Circumstantiae, 2003, 468~471. (in Chinese) [6]Yu Song, Xiaoyan Tang, Shaodong Xie, et al. Source apportionment of PM2.5 in Beijing in 2004. Journal of Hazardous Materials, 2007,146 (1-2):124~130. (in Chinese) [7]Ren Zhenhai, Huang Meiyuan, Dong Baoqun, et al. Studies on Transport of Acid Substance in China. Beijing, China, 1995. (in Chinese) [8] Zhao Xiujuan, Zhang Xiaoling, Xu Xiaofeng et al. Seasonal and diurnal variations of ambient PM2.5 concentration in urban and rural environments in Beijing . Atmospheric Environment, 2009, 43(18): 2893~2900. [9]Sun Zhenhua, Feng Shaoyuan, Yang Zhongshan, et al. Primary Analysis of the Precipitation Characteristics for Beijing during the Period from 1950 to 2005. Journal of Irrigation and Drainage, 2007, 26(2):12~16. (in Chinese)
277