Yizhen Chen

Efficiency of mitigation measures to reduce particulate air pollution—A case study during the Olympic Summer Games 2008 in Beijing, China

Atmospheric particles were studied before, during, and after the period of the Olympic Summer Games in Beijing, China, in August 2008 in order to investigate the efficiency of the mitigation measures implemented by the Chinese Government. Total suspended particles (TSP) and fine particles (PM(2.5) and PM(1)) were collected continuously from October 2007 to February 2009 and were analyzed in detail with regard to mass and element concentrations, water-soluble ions, and black carbon (BC). Mass as well as element concentrations during the Olympic air quality control period were lower than the respective concentrations during the time directly before and after the Olympic Games. The results showed that the applied aerosol source control measures, such as shutting down industries and reducing traffic, had a huge impact on the reduction of aerosol pollution in Beijing. However, the meteorological conditions, especially rainfall, certainly also contributed to the successful reduction of particulate air pollution. Coarse particles were reduced more efficiently than finer particles, which indicates that long-range transport of atmospheric particles is difficult to control and that presumably the established mitigation area was not large enough. The study further showed that elements from predominantly anthropogenic sources, such as S, Cu, As, Cd, and Pb, as well as BC, were reduced more efficiently during the Olympic Games than elements for which geogenic sources are more significant, such as Al, Fe, Rb or Sr. Furthermore, the mentioned anthropogenic element concentrations were reduced more in the finer PM(2.5) samples whereas geogenic ones were reduced stronger in TSP samples including the coarser fraction. Consequently, it can be assumed that the mitigation measures, as intended, were successful in reducing more toxic and health-relevant particles from anthropogenic sources. Firework displays, especially at the Opening Ceremony, could be identified as a special short-time source for atmospheric particles during the Olympic Games.

The influence of governmental mitigation measures on contamination characteristics of PM2.5 in Beijing

Beijing, the capital of China, has become one of the most air-polluted cities due to its rapid economic growth. Weekly PM2.5 samples-collected continuously from 2007 to 2010-were used to study the contamination characteristics of atmospheric particles and effects of governmental mitigation measures especially since the 2008 Summer Olympic Games. PM2.5 mass concentrations during the sampling period were reduced compared to the previous studies before 2005, although they were still too high in comparison with environmental standards of China and many other countries as well as WHO standards. Results of principle component analysis show that elements of primary anthropogenic origin had an obvious decline while elements mainly from the natural environment kept a relatively stable course. The governmental macro-control measures influenced both anthropogenic and geogenic sources, but they also led to some pollution peaks prior to implementation of the respective measures. Some element concentrations correlated to the restrictiveness of relative measures, especially during different traffic restrictions. The comparison with other countries and international standards shows that there is a long way to go in order to improve air quality in Beijing, and that governmental mitigation measures need to be continued and reinforced.

Spatio-temporal variations of black carbon concentrations in the Megacity Beijing

The spatial and temporal distribution and the flux of black carbon (BC) concentration in Beijing were continuously investigated over a two-year period at five sites to highlight the relative influence of contributing sources. The results demonstrate firstly that there is significant spatio-temporal variability of BC in Beijing. Highest concentrations occurred during winter primarily due to stagnant meteorological conditions, and seasonal BC sources, such as coal combustion for heating purposes. Biomass burning was identified as a minor seasonal source during the summer months. BC also varied spatially with higher concentrations in the SE of Beijing and lower concentrations in the NW, due to the differing emission intensity of various local BC sources such as traffic and industry. Frequently, overnight BC concentrations were higher due to specific meteorological conditions, such as the lower urban mixing layer height and various anthropogenic activities, such as exclusive night-time heavy duty vehicle traffic in the inner-city.

Seasonal Trend of Water-Soluble Ions at One TSP and Five PM2.5 Sampling Sites in Beijing, China

Weekly PM2.5 samples were taken at five sites, positioned along a transect from NW to SE through Beijing. Additionally, TSP samples were collected at one site. The study includes data from January to December 2006. Four water-soluble anions (sulphate, nitrate, chloride and fluoride) and five cations (sodium, ammonium, potassium, magnesium and calcium) could be detected by Ion Chromatography. A seasonal, as well as a spatial trend has been revealed concerning mass concentration and composition. The knowledge of these temporal and spatial characteristics of the aerosols is important for the assessment of the atmospheric pollution in Beijing especially with regard to negative health effects.

On the use of an explicit chemical mechanism to dissect peroxy acetyl nitrate formation

Peroxy acetyl nitrate (PAN) is a key component of photochemical smog and plays an important role in atmospheric chemistry. Though it has been known that PAN is produced via reactions of nitrogen oxides (NOx) with some volatile organic compounds (VOCs), it is difficult to quantify the contributions of individual precursor species. Here we use an explicit photochemical model--Master Chemical Mechanism (MCM) model--to dissect PAN formation and identify principal precursors, by analyzing measurements made in Beijing in summer 2008. PAN production was sensitive to both NOx and VOCs. Isoprene was the predominant VOC precursor at suburb with biogenic impact, whilst anthropogenic hydrocarbons dominated at downtown. PAN production was attributable to a relatively small class of compounds including NOx, xylenes, trimethylbenzenes, trans/cis-2-butenes, toluene, and propene. MCM can advance understanding of PAN photochemistry to a species level, and provide more relevant recommendations for mitigating photochemical pollution in large cities.

Size distributions of aerosol sulfates and nitrates in Beijing during the 2008 Olympic Games: Impacts of pollution control measures and regional transport

For the 2008 Olympic Games, drastic control measures were implemented on industrial and urban emissions of sulfur dioxide (SO2), nitrogen oxides (NOx) and other pollutants to address the issues of poor air quality in Beijing. To investigate the effects of SO2 and NOx reductions on the particulate sulfate and nitrate concentrations as well as their size distributions, size-segregated aerosol samples were collected using micro-orifice uniform deposit impactors (MOUDIs) at urban and downwind rural sites in Beijing before and after full-scale controls. During the sampling period, the mass concentrations of fine particles (PM1.8) at the urban and rural sites were 94.0 and 85.9 μg m−3, respectively. More than 90% of the sulfates and ∼60% of nitrates formed as fine particles. Benefiting from the advantageous meteorological conditions and the source controls, sulfates were observed in rather low concentrations and primarily in condensation mode during the Olympics. The effects of the control measures were separately analyzed for the northerly and the southerly air-mass-dominated days to account for any bias. After the control measures were implemented, PM, sulfates, and nitrates were significantly reduced when the northerly air masses prevailed, with a higher percentage of reduction in larger particles. The droplet mode particles, which dominated the sulfates and nitrates before the controls were implemented, were remarkably reduced in mass concentration after the control measures were implemented. Nevertheless, when the polluted southerly air masses prevailed, the local source control measures in Beijing did not effectively reduce the ambient sulfate concentration due to the enormous regional contribution from the North China Plain.

The Effect of Government Policies on the Temporal Development of Contamination Characteristics Within the Aerosol Distribution in Beijing, China

To host Green Olympic Games, the Beijing municipal government took comprehensive measures to improve air quality in 2008, which partly are still in force in 2012. The aim of this study is to investigate the temporal distribution of aerosol contamination characteristics and their variations under different government intervention policies. PM2.5 samples were collected continuously from 2007 to 2010 in the north of Beijing City. Element concentrations were analyzed by HR-ICP-MS. Results showed that concentrations of traffic-related elements such as Sn, Sb and Pb varied with the strength of traffic restrictions. Elements like Cr, Co and Ni, which are correlated with industries, were reduced under special policies like the relocation of Capital Steel Company. In general, the improving air quality demonstrates the success of government intervention policies although still the concentrations are too high if compared to international threshold values.

Mobility of trace metals in urban atmospheric particulate matter from Beijing, China

Total suspended particles (TSP) and particulate matter ≤ 2.5 µm (PM2.5) from Beijing, China, were studied for a time period of three years (2005– 2008). Beside the total mass and the element concentrations, also the chemical fractionation and bioavailability of various elements was investigated by applying a four-step sequential extraction scheme.

Source Identification and Seasonal Variations of Carbonaceous Aerosols in Beijing—A Stable Isotope Approach

Carbonaceous aerosols constitute an important part of atmospheric particles in urban areas. Within this study, total carbon (TC) was investigated in total suspended particulates (TSP) and fine particles (PM2.5) collected in the megacity Beijing, China. Beside mass and TC concentrations, also stable C isotopes were analyzed by isotope ratio mass spectrometry (IR-MS) coupled to an element analyzer (EA). Carbon isotope ratios (δ13C) can serve as a fingerprint for source identification, because different source materials have characteristic δ13C values.