The Characteristics of Air Pollution and its Control Under the urbanization in Beijing

XIAOYAN TANG
(Center of Environmental Sciences
, Peking University)

China has experienced the rapid economic growth (up to 7 to -8 percent % of gross domestic product [GDP] per year) since the mid-dle of 1980s. . This shorrapid growth in such a short period of time has but fast growth of economy not only leaded to a remarkable increase inof material wealth enrichment and a higher standard of living standard, but has also caused the severe environmental pollution,problems in environment pollution, in particularly the atmospheric pollution.

The problem atmospheric pollution problem in China was first has been observed in thesince 1970’s with . The first notice had been put on the industrial emissions of sulfur dioxide (SO₂) and TSP( total suspended particulates (TSP)). In the 1980’ss, the acid rain whas been detected in the major cities in the southern part of the countryChina. This was caused which was mainly caused bby the SO₂ emitted from coal combustion, which accounts for more than due to the fact that the coal possessed more than 70 percent of % of fuel consumption in China, Beijing as well. In the 11990’s, the number of the road vehicles on roads transportation and the population of motor vehicles increased very rapidly, especially in the medium-sizediddle and large sized cities. In Beijing, the number of population of vehicles increased by a factor of 4, from 0.5 million in year 1990 to 2.0 million in year 2002. The drastic riose up ofin the number of vehicles and rapid quick development of industries in cities has leaded to the worsening air quality, particularly higher to the enhencement of air concentrations of nitrogen oxides (NO_x an) andd particulates. HThe high levels of ozone concentration werecould be frequently observed in the summer andor fall in several big cities,. and Since then, the visibility in the urban areas in many cities continues to deteriorate. has become worse and worse. For the past four years, PM₁₀ Besides the SO₂ and NO_x, the PM10 has been reported as the predominant pollutant in Beijing and most of cities in Chinathe cities in China for more than 3 years.

Economic growth and increasing urbanization in China have caused a tremendousn increase in the extensive cconsumption of energy and tremendous emissions of exhausts of SO₂, NO_x, volatile organic compounds (VOCs), and TSP, suspended fine particles etcand other pollutants.. These primary pollutants are not only dispersed in the air and move to surrounding areas, upon the meteorological condition and transport to a distance, but they also react photo-chemically reacted to generate secondary pollutants. under the exposure of ultra- violet part of the solar radiation (UV-light). The well known Pphoto- chemical smog, (the ground- level of ozone), isare produced fromfrom the reaction of NOx andplus VOCs reactions with under the ultra-violet radiation. Gthe as- phase SO₂, NO_x and VOCsorganics can be transformed into the fine particles (<PM_2.5). ), which The fine particles have a large surface areas and can played a role as catalyzed further reactions on the particle surface (Figure 1). Thus, the reactions between pollutants become more complexly moving to and fro, leading to buildup of larger amount of making the secondary pollutants aggregated and concentrated in the air and causinged severe air quality problems(pic. 1).

This kind of phenomenona has already been observed especially in several mega cities, such as Beijing, Guangzhou, and Shanghai etciddle sized .. This Such kind of air pollution has problem could be indicated by three remarkable characteristics: (1) a high concentration of fine particles that adversely affect visibility; (2) a high capacity for atmospheric oxidation; and (3) regional environmental effects.

Since 1998 a series of studiesresearch supported by the central and municipal government have been focused on works are emphasizedidentifying on finding the characteristics of air pollution, pollution formation mechanisms, source apportionment and pollution control techniques etc. In this paper the characteristics of air pollution in Beijing city and the pollution related control issues are briefly introduced.

High Concentrations level of Ffine Pparticlesc and Adverse Effects on Visibility

impact on the visibilityThe visibility problem has affected Beijing for several years., the capital of China, has been suffered for several years by the visibility problem. The Ccitizens often complain complained that they it was rarely see opportunity to enjoy the beautiful clean blue skiesy and with white clouds in the Beijing area. AA study ofn the relationship betweeonf visibility andwith concentrations of fine particles(PM_2.5) in had been conducted in 1999–-2000. Results showed a direct correlation in every season. that the atmospheric visibility was closely related to the mass concentration of PM2.5 in air, an obvious negative relationship of which could be found in any season of the year in Beijing area. Results also showed that the massthe concentration of PM_2.5 in the summer and winter (a daily average of 60 to 80 ug/M³) wwas higher than the National Air Quality standard in the United States (65 ug/M³). rather high in the urban part of Bejing, the daily average of which easily reached up to 60 to 80 ug/M³ in the summer and winter, exceeding the daily average 65 ug/M³ of the national air quality standard in USA. In winter, the diurnal profile of PM_2.5 mass concentration was highest at midnight presented a special high peak in the midnight every night (s(Figure 2), ee Pic. 2). It seemed probably because that the heavy traffics was permitted to pass through the metropolitan area only after 8:00 p.m. by the transportation policy set up by Beijing municipal government. In summer, the PM2.5 reached the peak concentration at noon due to the photochemical reaction. It is noticeable that the mass concentration of PM2.5 in Beijing city possessed around 40-50% of mass concentration of PM10. Source apportionment study showed that the major sources of PM2.5 were transportation, industry and secondary transformation.

High Capacity for2．Enhanced Aatmospheric Ooxidationc

Ozone as a secondary product is produced simultaneously with a series of different kinds of oxidants, such as atmospheric free radicals (e.g., OH, HO₂, RO, RO₂, etc.). High concentrations of High oOzone and concentration with high free radicals in the atmosphere lead to a high potential for the oxidation of concentration represents the high potential oxidation capacity of the atmosphere, where the oxidation rates of primary pollutants (SO₂ and NO_x) to secondary pollutants (sulfate [SO₄^2- ] and nitrate [NO₃^-]). in will be increased. Thus the increasedenhanced concentration of secondary pollutants in the air is expected. It pris probably is the major reason for the increasingly serious visibility problem.of why the visibility problem happened in urban area is getting so serious.

SThe short-term and long- term exposure to ozone-rich airin the air rich of ozone can cause eye irritation, plant damage, respiratory problems, and the deterioration of shorten the life of rubbers and paint.ings, especial injurious to the human respiratory system. The World Health Organization has suggested that one hour of exposure in air should not exceed 75 to- 100 ppb. for protecting the human health. Therefore, reducing the number and severity of How to decrease the ozone episodes and lowering the levels of atmospheric ozonethe concentrations have in air becomes one of the major health concernss of the the municipal government. and the residence as well

3．The Rregional Effectsdimension of Aair Ppollution

In just Within 20 years, urbanization has increased the urbanization in China was expanded dramatically in Beijing-Tianjin-Bohai Bay region, and where the distances between cities have steadily were reduced adecreased.nd reduced. As tThe density of cities has was increasedincreased, and in some cities suburbs were even not existed. tThe regional impact of air pollution has become increasingly noticeable.could be frequently observed in those circumstances.

In recent years, the field measurements of air pollutants with meteorological observations and the model simulationsing simulation oof air quality on ain regional scale have been conducted in this region (Figure 4). The rResults showed that the pollutants, in particularly secondary pollutants such as fine particles and ozone, were distributed regionally under certain meteorological conditions.

Three3-dimensional numerical modeling model study offor air quality in Beijing with the surrounding areas has been conducted. The results (pic. 5) showed that showed that the ozone episodes and the contributions toof ozone formation from different sources were urrounding places depended upon the meteorological conditions. The simulation results of One of the simulation results in June 27, of 2000, are shown in Table 1was shown in table 6. The ozone daily maximum concentration of up to 200 ppb appeared at 1 to 2 p.m.13:00 – 14:00 in the Beijing downtown area;, andhigh ozone covered a large region, including some part of Tianjin and surroundingsneighborhoods. The mModel calculation indicatesd that the main contributor to the ozone episode at that time was mainly contributed by the precursors from Tianjin city and residential areasits .

The Efforts of Air Pollution control in Beijing

Since 1998 Beijing Municipal Government has attached importance of the imperative duty on control air quality in Beijing. A multi-phased control plan for taking urgent measures to reduce the air pollutants was issued and announced to public in Dec. 1998. 9 phases of control measures had been implemented until the end of year 2003. The control measures include not only the reduction of emission of major pollutants, such as SO2, NOx and particulate matters, but also the organic substances (VOC, volatile organic compounds) in consideration of the severe situation of secondary pollution. A series of detailed measures for decreasing the emission has been listed and taken, such as desulphurization for coal-burning power plants, the substitution of cleaner fuels for burners and boilers, creation of the “coal-free combustion areas”, execution of Europe-II standard for motor vehicles, acceleration of phase out process of aged cars, replacement of the cleaner fuels for buses and taxes, control of the fugitive dust emission from the building sites and road, increasing the greenly space and fields, control of the emission from fuel service station, restaurants and solvents etc.. The enhancement of management, legislation, regulation and execution were also included and conducted.

The results of reduction of emission had been evaluated after implementation of four phases’ activities of this control plan in 2001. The total reduction in these four phases for SO2, NOx and PM10 were 65,320 tons, 25,500 tons and 18,300 tons, respectively. The air quality monitoring showed that the yearly average concentration changes from 120 mg/m³ to 71 mg/m³ for SO2; 152 mg/m³ to 127 mg/m³ for NOx and 176 mg/m³ to 162 mg/m³ for PM10.

The ambient air Quality data of gas pollutants and measured particulates concentrations since 1998 are listed into Tables 2.

Conclusion

RapidThe economic growth combined with the urbanization in China has caused severed air pollution problems in Beijingthe . of China. These problems are proving not easy to solve because of the complex nature of the pollution. Due to the rapid development in China the air pollution problem in urban area brings out more comprehensive and complex characteristics, which caused the difficulty in solving the problem. Many Studiesresearch have been focused on works are emphasizedidentifying on finding the characteristics of air pollution and the formation mechanisms, source apportionment and control techniques. identification the Much attention and urgent action have been focused onare also attracted on the control measures andthe policy issues. The remarkable improvement of the air quality has been observed after five year’s strengthened actions. Beijing expects that the air pollution problem will could be reduced promptly in during the next several years.

figure captions

FIGURE 1 The chemical behavior of pollutants in the air.

FIGURE 2 The diurnal profile of PM_2.5 mass concentration in winter (above) and summer (below) in 1999 in Beijing.

FIGURE 3 The diurnal profile of ozone concentration measured in different years at the Peking University site.

FIGURE 4 The simulation area, including Beijing municipality and surrounding areas, inby the three3-dimenstional air quality model in three scales of nesting grids.

Table able1.6. The c Contributions of Pprecursors (NO_x and VOCs) from Ddifferent Pplaces to the Formation of Oozone formation in Ddowntown of Beijing (1 –13:00-2 p.m.,14:00, June 27, 2000).

Source region	NOx Ccontribution	VOC Ccontribution	Total Ccontribution
Beijing downtown	9.9%	14.7%	24.6%
Southeast part of beijingBeijing	5.6%	3.5%	9.1%
Tianjin and vicinity	9.3%	23.8%	33.1%
Southern part of Hebei Province	3.3%	7.9%	11.2%

Table 2. 1998-2003 the Ambient Air Quality (mg/m³) in Beijing city

	SO2	NO2	CO	PM10	TSP
1998	0.120	0.074	3.3	-	0.378
1999	0.080	0.077	2.9	0.180	0.364
2000	0.071	0.071	2.7	0.162	0.353
2001	0.064	0.071	2.6	0.165	0.370
2002	0.067	0.076	2.5	0.166	0.373
2003	0.061	0.072	2.4	0.141	0.252

Table 3. The days of achieving the National Air Quality Standard in a year (by API)

	The days achieving and better than API II (days)	%
2000		48.4％
2001	185	50.7％
2002	203	55.6％
2003	224	61.4％