Impact of Summertime Weather System Activity on Air Quality Variations Over Beijing and the Implications
It is very known that there is a clear relationship between air quality (in particular, PM10 concentrations) and meteorological parameters (prevailing wind conditions) in Beijing. In this study, by analyzing the PM10 concentrations and wind characteristics at Peking University monitoring station and the large-scale wind patterns during summertime over Beijing, we found the PM10 levels show repeated cycles at the synoptic scale that can be expressed by a new component meteorological index defined by the meteorological parameters. By reviewing the summertime air quality variations in 2006 and 2007, we found that activity of mid- latitude baroclinic waves and the subtropical high of the western pacific are major contributors to air quality variability over Beijing in the summer. This should be good news for air quality forecasting in Beijing as our understanding of mid-latitude baroclinic waves is quite good, and these systems are predicted rather well by most state-of-the-art numerical weather prediction models. We further studied an inter-annual variation of Air pollution Index (API) recorded at 39 monitoring stations over eastern China, and its relationship with the monthly mean atmospheric circulation at an intra-seasonal scale. A physical pattern showing an anti-correlation of north and south of eastern China was identified by empirical orthogonal function and singular value decomposition analyses. Analysis of the monthly mean circulation fields and API showed that there is a clear relationship between the inter-annual variability of monthly averaged air quality over eastern China and the large scale circulations, including inter-annual movement of the western pacific subtropical high, the strength of the low-level winds, and the location of the Meiyu front over China.
Source Analysis of Volatile Organic Compounds by Positive Matrix Factorization in Urban and Rural Environments in Beijing
This study applies advance receptor model positive matrix factorization (PMF) source analysis to one-hour resolution VOC data collected at Yufa (rural site) and Peking University, or PKU (urban site), in Beijing. A range of major VOC sources was identified, including vehicle emissions, LPG, coal combustion and biogenic emissions. Vehicle activities contributed approximately 62% of VOC loading and 55% of ozone forming potential at the PKU site, compared to 38% of VOC loading and 42% of ozone forming potential at Yufa. These results indicate that the control of vehicle emissions is essential to alleviating VOC pollution, particularly in urban Beijing. We found that VOC emission strengths are relatively consistent throughout the day in the rural area; variation of mixing height therefore is a controlling factor for ground-level VOC concentration. While in the urban area, both vehicle activity and variation of mixing height strongly impact VOC levels. Local sources within Beijing appeared to contribute most of the VOCs recorded at both urban and rural areas. However, as some of the VOC species are quite reactive, VOC emitted from distant sources would have been depleted during transportation, concurrent with the formation of secondary pollutants such as ozone and sulfate. Such depletion would mean that this source apportionment analysis would tend to overestimate the ozone forming capacity of local VOC sources compared to emissions from distant sources. Nevertheless, this study illustrates that high-resolution VOC measurements, especially those with a sampling frequency on the scale of less than one day, combined with PMF, can make a strong contribution to our understanding of pollutant emissions and transport characteristics, and is a useful tool with which to formulate effective pollution control strategies.
Cloud chemistry at Mt. Tai in Eastern China
Clouds are important processors of atmospheric trace gases and particles. Clouds play a substantial role globally in the transformation of gas phase sulfur dioxide to particulate sulfate. In order to assess the ability of regional clouds to oxidize sulfur dioxide, spring and summer field studies of cloud chemistry were conducted in 2008 at Mt. Tai, an isolated peak on the NE China plain that is frequently intercepted by clouds and experiences air pollution transport from a variety of source regions. Samples of cloudwater were collected at Mt. Tai with single and multi-stage Caltech Active Strand Cloudwater Collectors and analyzed for pH and concentrations of major inorganic ions, total organic carbon, S(IV), hydrogen peroxide, Fe, Mn, and organic acids. The study also included measurements of key trace gases including sulfur dioxide, ozone, and hydrogen peroxide. A wide range of cloud pH was observed, extending from below 3 to above 6. High concentrations of cloudwater sulfate were consistent with abundant sulfur dioxide emissions in the region. Despite its quick reaction with sulfur dioxide in cloud droplets, high concentrations of hydrogen peroxide were measured in some clouds. In addition, large concentrations of organic matter were observed in some sampled clouds. This presentation will provide an overview of the composition of clouds measured at Mt. Tai during spring and summer and will examine the capacity of the regional atmosphere to support aqueous phase sulfur oxidation.
An Examination of the Impact of Air from China on Air Quality in Hokkaido, Japan Before, During, and After the Beijing Olympics
During July through September 2008 pollution controls in China associated with the Beijing Olympics led to a
decrease of emissions of about 30%, as observed by NASA's OMI instrument on the Aura satellite. Pollution
from China has an impact on air quality throughout East Asia. In this presentation, we examine specifically the
impact of China's pollution on Hokkaido, Japan through the use of Aura satellite data (2004 - 2008),
ozonesonde data (2000 - 2008), and data from air quality surface monitors (2000 - 2008). We also examine
the year-to-year variability in meteorological flow regimes through trajectory model simulations of transport to
Japan from the areas around Beijing and Shanghai, China and around Seoul, South Korea in order to
apportion remote sources of pollution. These simulations indicate that while August 2008 experienced less
frequent incursions of air from Beijing than previous years, at least one pollution event in Hokkaido in early
August can be linked to the Beijing area.
Impacts of Emission Reduction Scenarios on Regional Climate and Local Air Quality for the 2008 Beijing Olympic Games
Beijing implemented a long term emission reduction program in 2001 when it won the bid to host the 2008 Summer Olympic Games. During the summer of 2008 Beijing increased its emission reduction effort by integrating short term strategies such as temporally shutting down factories, freezing constructions, and automobile control. Taking advantage of emission reduction measures, numerical simulation experiments are being carried out with the Weather Research and Forecasting model with chemistry module (WRF-Chem) to examine aerosol-cloud-precipitation interactions in the Beijing metropolitan region during the period of the 2008 Olympic Games. Analyses of TRMM 3B42V6 and MODIS Terra L3C5 datasets show that August 2008 was a period of above average precipitation and below average aerosol loadings, relative to observations during the past 10 years. This study is based on numerical simulations with two emission scenarios, business as usual scenario and reduced emission scenario, to examine the impacts of emission reduction measures on regional climate and local air quality in the Beijing metropolitan region, as well as the role of cloud and precipitation processes in controlling the regional distribution of aerosols. Both of the high- resolution emission inventories were developed by the Institute of Atmospheric Physics, China, to represent the effects of emission reduction policies for the Olympic period. Intercomparisons with in-situ measurements are used to assess the capability for modeling aerosol-cloud-precipitation interactions on a regional scale. Analyses center on assessing "microphysical" and "stability" hypotheses linking aerosols to cloud and precipitation processes and examining the relative roles of precipitation processes, regional transport processes and emission reduction scenarios in producing the favorable air quality conditions during the Olympic period.
OMI measurements of SO2 pollution over Eastern China in 2005-2008
The Ozone Monitoring Instrument (OMI) on NASA Aura satellite makes global daily measurements of the total
column of sulfur dioxide (SO2), a short-lived trace gas produced by fossil fuel combustion, smelting, and
volcanoes. OMI seasonal to multi-year average images clearly show the world-highest consistent SO2
pollution in northeast China. China is the world's largest SO2 emitter, mostly due to the
burning of high-sulfur coal in its many coal-fired power plants, which lack the technology used in many other
countries to remove sulfur from smoke stack emissions. China's government has
instituted nationwide measures to control SO2 emissions through the adoption of flue-gas desulfurization
technology on new power plants; and even greater measures were adopted in the Beijing area in anticipation
of the Olympic Games. To study the environmental effects of the emission controls we compared OMI SO2 time
series over eastern China for 2005 through 2008. The time series have been done as 7-day running means of
the cloud-free daily observations. By mid-March we started to see substantial periods of lower SO2 values in
2008 compared to 2007, and by mid June the 2008 values were consistently lower than 2007 and prior years.
The decline is widespread with highest SO2 typically located to the south and southwest of Beijing in regions
with large clusters of power plants and also around Shanghai. The decline also lasted beyond the Olympic
season. We do not yet know to what extent the economic downturn in China (and reduced industrial
production) contributed to lower SO2 levels in the fall of 2008. We have also compared the observed and
modeled fields using University of Iowa STEM model for the period June - September
2008. The model provided SO2 vertical distributions as well as aerosol vertical profiles that were used to
correct OMI operational SO2 retrievals and improve the comparisons. The OMI SO2 changes in 2008 have also
been compared with the estimated changes in SO2 emissions derived from a bottom-up analysis of the SO2
reduction measures put into place for the Olympics. Finally we present our plans to use the OMI SO2 columns
to provide a top-down constraint on SO2 regional emissions.