The scope of this study is to develop a comprehensive understanding of the an-thropogenic and geogenic aerosol pollution in Beijing. The characterization of the dominant geogenic and anthropogenic sources of particulate air pollution in the megacity Beijing, the complex mixing of particles from both source groups and their spatio-temporal variability, as well as the influence of mitigations mea-sures on particulate air pollution are the main aspects considered in this study.
The central questions of this work are:
• Spatio-temporal variations of urban aerosols
– What is the concentration and composition of particulate matter in Beijing?
– Which are the main parameters influencing seasonal variations?
– Which seasons are most critical with regard to adverse health effects?
– Which are the main parameters influencing spatial variations?
– What are the most important geogenic and anthropogenic sources?
• Bioavailability of toxic element concentrations
– Which are the elements with highest mobility and biovailability?
– Which of those bioavailable elements are abundant and, thus, the most critical for possible negative effects on human health?
– Which seasons have highest concentrations of bioavailable metal con-centrations?
– Which are the main sources for the bioavailable element concentra-tions?
• Influence of mitigation measures on aerosol concentration and compo-sition
– How fast and to what extend was the particulate air pollution reduced?
– Which particle size class was reduced most efficiently?
1.5. SCOPE OF THE PRESENT WORK 11 – To what extend did the weather conditions influence the particle
de-crease?
– What was the chemical composition of atmospheric particulate matter during the Olympic Games and how did the composition change?
– Which sources can be identified to contribute to the aerosol concen-tration during the Olympic Games?
– How fast and to what extend did the aerosol pollution increase again after the Olympic Games?
• Interaction between geogenic and anthropogenic particles on a single particle level
– Which are the typical geogenic and anthropogenic particles in Bei-jing?
– Which kind of particle interactions can be found?
– To what extend act geogenic particles as scavengers for small anthro-pogenic particles?
These questions will be discussed in detail in chapters 4, 5, 6, and 7, respectively.
Chapter 2
Study area: Beijing
Atmospheric pollution constitutes a big challenge for densely populated urban areas and megacities (generally defined as cities with more than 10 million in-habitants), in particular. The rapid economic growth in China (GDP: annual growth rate of about 10%, National Bureau of Statistics of China, 2009) comes along with a rapid expansion of the urban population and a huge increase in en-ergy consumption. Urban agglomerations developed extremely fast in the last decades. While in 1980 only 19% of the Chinese population lived in cities and towns, the number increased to 26% in 1990, 36% in 2000 and 45% in 2007 (Na-tional Bureau of Statistics of China, 2009). Worldwide more people are living in urban compared to rural areas by now (UN, 2008).
2.1 Beijing and its surroundings
Beijing, the capital of the People’s Republic of China, lies on the northwest bor-der of the Great North China Plain, at 39◦56’ N and 116◦20’ E and occupies a total area of 16,410 km3. While the city is connected to the North China Plain in the south, it is surrounded by the Yanshan Mountains in the west, north and northeast. It neighbours the Tianjin Municipality in the east, and borders Hebei Province on three sides (north, west and south). In 2005, approximately 11 mil-lion inhabitants were living permanently in Beijing (Beijing Municipal Bureau of Statistics, 2009). Additionally, migratory worker increased the population to approximately 15 million. In 2007, 67% of the total area was used for farming, 20% were building sites, while 13% were unutilized (Beijing Municipal Bureau of Statistics, 2009). The Beijing-Tianjin-Hebei economic band is located in the center of the vibrant economic area of Northeast Asia, which is one of three major rapidly developing economic zones in China (Xin et al., 2010).
14 CHAPTER 2. STUDY AREA Anthropogenic as well as geogenic sources for air pollution in Bejing are abun-dant. The total energy consumption in China rose from 6×108 t of SCE (Standard Coal Equivalent) in 1980 to 13×108 in 2000 and 26.5×108 in 2007. Coal still is the major energy source, constituting about 70 % of the total energy consump-tion (2.6 bn tons SCE) in 2007 (Naconsump-tional Bureau of Statistics of China, 2009).
In Beijing, coal is used both industrially and domestically. Domestic heating in Beijing usually starts in mid-November and ends the following March (He et al., 2001). Emissions from various kinds of industry contribute to overall air pollution. Traffic is considered another major anthropogenic source including direct emission products (e.g. soot) as well as particulate matter from abrasion (tire and brake wear) and resuspension processes. In 2005, there were 2.1 mil-lion vehicles in Beijing, with 1.5 milmil-lion private ones, among which 0.92 milmil-lion were cars. The number of vehicles increased to 3.2 million in 2008, with 2.5 million private vehicles including 1.7 million cars (Beijing Municipal Bureau of Statistics, 2009). In the last decades, many new high-rise buildings were con-structed in Beijing, hindering the dispersion of air pollutants (Hao et al., 2000;
Liu et al., 2009). Construction activities also constitute an important dust source in Beijing. In preparation for the Olympic Summer Games, which took place in Beijing in August 2008, the amount of construction sites strongly increased.
The anthropogenic air pollution is superimposed by geogenic dust from bare soils transported over a short-range and from semi-arid/arid areas northwest of Beijing due to long-range transport. Dust storm episodes regularly occur in spring due to the meteorological conditions and especially if the wind direction is from NW (see section 2.2).