PM2.5 monitoring and mitigation in the cities of China.

I the past decade, the air quality of China has been drawing great concern in the face of the country's rapid economic development. Nowadays, suspended particulate matter (PM) is considered to be the most serious pollutant in the metropolitan areas around the world due to its adverse health effects, including cardiovascular diseases, respiratory irritation, and pulmonary dysfunction. In respect of PM, the fine PM (PM2.5: aerodynamic diameter of particle ≤2.5 μm) poses the greater health risks, compared with the coarse PM (PM10: aerodynamic diameter of particle ≤10 μm) because the increased surface areas have high potential to adsorb or condense toxic air pollutants (oxidant gases, organic compounds, and transition metals). China codified a PM10 standard for ambient air quality in 1996, however, China does not have a PM2.5 standard or emission rule at present. In December 2011, a severe debate focusing on PM2.5 occurred among the experts, media and public in Beijing, China. This debate is dust storms, smog, fog, and haze events occurred in the north of China with a high frequency, recently, which was significantly attributed to PM2.5 (Figure 1, a photo in Beijing, China). Actually, previous studies reported the PM2.5 in the biggest cities of China was in the range of 20−80 μg/m in the past decade, which highly exceeds U.S. PM2.5 standards (primary standard: 15 μg/m; secondary standard: 35 μg/m). Based on the public requirement, in order to provide adequate health and environmental protection, the Ministry of Environmental Protection of the People’s Republic of China decided to implement a national PM2.5 monitoring program. This promotes China government to pay more attention to the common water and air pollution, rather than the climate change. According to the Shengxian Zhou, Minister of China Environmental Protection Ministry, the monitoring program will be accomplished by “Four Steps”: First, designate the areas of Beijing, Shanghai, Guangzhou, and 31 capital cities of provinces where compliance monitoring of PM2.5 and ozone must be performed by 2012. Second, designate another 113 cities of high environmental standard and attention to start monitoring by 2013. Third, all the county level cities must start monitoring the PM2.5 by 2015. Fourth, a new emission rule and PM2.5 standard based on the monitoring data will be executed nationwide by 2016. After 2016, all the cities and associated emission have to satisfy the requirement of the new criteria. Meanwhile, the real time PM2.5 and ozone monitoring records and relevant information will be released to the public. However, the financial problem is a main hassle for PM2.5 and ozone monitoring, from the instrument installation at the beginning to the monitoring station maintenance in the future. The U.S. Environmental Protection Agency issued a PM2.5 standard in 1997. It took about 8−10 years to make the designated areas more effective and by strengthening their standard for particle pollution. Currently there are over 1200 monitors in place nationwide to provide real time PM2.5 concentration levels in the U.S. Thus, the implementation in China would take several years to develop a mature PM2.5 monitoring and recording network. However, the process to achieve this goal of developing a PM2.5 monitoring network is complicated and difficult. There are several noteworthy measures and manners. First of all, the monitoring station selection is critical to provide the representative ambient air data. For instance, the Cities of Los Angeles and Houston, which are similar to Chinese metropolitan cities, have 10−15 PM2.5 monitoring stations deployed which cover the representative areas with industry, transport, and household emissions. The installation and operation of PM2.5 monitoring are not only to observe the maximum concentration, but also to find out the human exposure levels. Second, the PM2.5 emission inventory data should be set up, which include the power plants, wild fire emissions and other sources. This will be helpful for the PM2.5 prediction in the air quality modeling and identification of the most effective strategies for emission controls in the future. Third, besides the regular PM2.5 mass concentration measurement, speciation monitoring is also important, which would be useful not only for identifying the evocators of adverse health effects but also for characterizing emission sources. In fact, the components of PM2.5 can reflect the predominant emissions of China, (SO2, NOx, CO, and CO2), as well as the distinct local emissions. Therefore, the proper locations and measures for speciation monitoring are significant. Fourth, while implementing the control of PM2.5 emissions, it has to be recognized that air quality is a regional issue. Isolated pollution control strategy in one area is not sufficient to improve the air quality as the neighboring provinces emissions exert significant influence on the local air quality. The pollution control through the regulation of vehicle and industry emissions in the metropolitan areas can be initiated first. Finally, the application of geographic information system and remote sensing combined with the air modeling may help to understand and map the PM2.5 spatial