Sources of local PM 2.5 pollutants Graphics: Xiangjun/GT

More than a quarter of the PM 2.5 pollutants in Shanghai in 2012 and 2013 originated from outside the city, new research shows. The Shanghai Environmental Protection Bureau released its most comprehensive study on the sources of PM 2.5 last Wednesday, revealing that PM 2.5 or fine particulate matter is the main air pollutant in the city. Based on weather data collected in 2012 and 2013, researchers at the air quality watchdog revealed that 74 percent of PM 2.5 came from local pollutants and the remaining 26 percent came from neighboring areas.

Most of the fine particles in the city air came from transport exhausts - cars, buses, trucks, ships, aircraft and off-road motors (like construction equipment or locomotives) and accounted for 29.2 percent of the pollution. The other major sources involved industrial waste (28.9 percent), coal burning (13.5 percent), dust (13.4 percent) and agricultural waste, straw and other biomass burning as well as domestic pollutants (15 percent).

Vehicle exhausts produce the most pollutants, accounting for more than 9.7 percent of the fine particles measured in the city, much more than in some of the cities in the Beijing-Tianjin-Hebei region. But the researchers found that Shanghai was less affected by coal burning than northern cities, where people rely on it for heating in winter. Researchers also found that Shanghai was less affected by dust than northern cities, because of the moist air and the city government's work in combating dust.

Sources change

The researchers reported that PM 2.5 sources changed and were affected by economic development, industrial transformation and city construction projects.

In 2012 and 2013, the level of fine particles produced by transport, like vehicles and ships, fell - the result, the report concluded, of the city government introducing tougher exhaust emission standards and banning high-polluting vehicles. The city ordered some 150,000 high-polluting vehicles off the road between 2012 and 2014, according to the Xinhua News Agency.

Shanghai was also less affected by coal burning and dust, after the city switched to cleaner energy and took measures to control dust. The researchers noted that the city needed to take more steps in the future to reduce other sources of PM 2.5, like domestic waste, agricultural pollution and biomass burning, which produce an increasing number of fine particles.

Unlike an earlier pilot study in 2012, when researchers analyzed data collected at two sampling sites over two months, this time more than 50,000 pieces of data were collected over two years from six sampling sites across the city. The researchers also separated pollutants carried from neighboring cities from local pollutants to make a more precise analysis.

Sources of local PM 2.5 pollutants Graphics: Xiangjun/GT

Neighboring cities

In this study, the researchers found that the level of fine particles carried to Shanghai from neighboring cities had risen over the levels recorded in the previous pilot study in 2012. They accounted for 26 percent of the fine particles around the city in the new research, rising from 21.5 percent in the 2012 study. The report said this reminded the Shanghai government that it had to improve cooperation with other cities and work together to control and prevent pollution.

"One of the heaviest pollution recordings occurred in the city on a December day in 2013, when PM 2.5 levels soared over 600 micrograms per cubic meter. According to our research, more than 50 percent of these fine particles were carried here from other cities," said Li Li, one of the environmental experts involved in the study. The World Health Organization's standard for safe air is 25 micrograms per cubic meter within a 24-hour period but China has set its recommended safe limit at 75.

The bureau researchers also found that the number of fine particles carried from other cities varied from season to season and changed with different weather conditions.

Shanghai started monitoring PM 2.5 in 2006, and began collecting and analyzing data in 2009. Over the past few years, the city carried out a series of studies targeting coal burning power plants, haze and other causes of air pollution. Using this comprehensive study, the city plans to build a network to monitor air pollutants.

"We will not only continue research on PM 2.5 sources, but also study the sources of every kind of heavy pollution, in order to offer specific suggestions to reduce air pollution," said Luo Hailin, an expert from the Shanghai Environmental Protection Bureau. At present there's a focus on studying pollution caused by ships. According to research in 2013 by the air quality watchdog, ships accounted for 5.6 percent of Shanghai's PM 2.5 particles.

Looking better

The Shanghai Environmental Protection Bureau reported last Thursday that Shanghai's overall air quality appeared better in 2014 than in 2013, due to the absence of extreme weather conditions and the city's work to control air pollution.

The bureau reported 281 days of "good" or "excellent" air quality in 2014, with an average AQI of below 100, an 11 percent increase from 2013. There were 84 polluted days, fewer than the 124 days in 2013. In 2014 there were four heavily polluted days, which was better than in 2013 when the city saw 21 heavily polluted days and another two severely polluted with the AQI surpassing 500.

In 2015, Shanghai will keep working to curb road traffic pollution, cutting the numbers of high-polluting vehicles, expanding the use of cleaner energy sources, updating boilers and furnaces at power plants, raising industrial emissions' standards and working with the authorities in neighboring provinces.

To date Shanghai has seen eight polluted days this year with the AQI peaking at 302 on Sunday night. The air quality watchdog reported that this was caused by pollutants from northwestern China and still conditions in Shanghai, and PM 2.5 is higher in winter and spring than in summer and autumn.

Just what is particulate matter?

The term fine particles, or particulate matter 2.5 (PM 2.5), refers to tiny particles in the air that are 2 ½ microns or less in width - a micron is about one thousandth of a millimeter. Larger PM 2.5 particles are about 30 times smaller than a human hair.

PM 2.5 pollution reduces visibility and causes haze when its levels are elevated. Outdoor PM 2.5 levels are most likely to rise on days with little or no wind.

The danger to health is that PM 2.5 particles can travel deeply into the respiratory tract and reach inside the lungs. Exposure to fine particles can cause short-term symptoms such as eye, nose, throat and lung irritation, coughing and sneezing and can affect lung function and exacerbate existing medical conditions.

PM 2.5 can come from outdoor and indoor sources. Outside, fine particles are produced by cars, trucks, buses and off-road vehicle exhausts, the burning of fuels like wood or coal and natural sources like straws. Fine particles can be carried long distances from their sources.

PM 2.5 is also produced by common indoor activities - smoking, cooking, fireplaces and fuel-burning space heaters.

When outdoor levels of PM 2.5 are elevated, experts say it's better to stay indoors. The citywide study involved looking at the sources of air pollutants and how much each source created. By analyzing the sources of PM 2.5, local environmental protection experts hope to be able to reduce pollutants at the sources.

Global Times