ENVIRONMENT/ECOLOGY

As the world’s second-largest economy, China has experienced severe air pol-lution with unprecedentedly high levels of PM2.5, i.e. particulate matter smaller than 2.5 μm in diameter. The Ministry of Environmental Protection of China released an air pollution monitoring re-port for the year 2013 for the 74 largest cities of China. The Beijing–Tianjin– Hebei (BTH) region was classified as having the poorest air quality.The annual average PM2.5 concentration of the 13 cities in the BTH region was 106μg/m3. None of these cities met the new an-nual China Ambient Air Quality Stan-dard (CAAQS), and 10.4–79.2 % of the total days in 2013 met the daily CAAQS. Seven cities ranked in the top 10 with poorest air quality in the country. In January 2013, there were severe regional haze events in the BTH region, with the highest hourly PM2.5 concentration in Beijing exceeding 900μg/m3 [1]. The deterioration of air quality is mainly because of the rapid economic growth and urbanization associated with heavy coal consumption, rapid increase in the number of vehicles, on-going construction and high population density [2]. Economic development in the BTH region is uncoordinated and inefficient. Outdated industrial techniques and equipment are still used in many cities in Hebei Province. Inefficient fuel consumption and lagging emission control measures have led to high pollution emissions. In addition, the topography favors pollutant accu-mulation under weak southerly winds o