Study shows PM1 air pollution is most harmful

A recent study led by Chinese scientists shows a strong link between smaller air pollution particles and a range of serious health conditions.

Scientists said the smaller the airborne particles, the more likely they are to cause illness, suggesting the need for monitoring of particulate matter of 1 micron or less in diameter — a category of pollution rarely monitored.

In recent years, many locations across the country have been blanketed with heavy air pollution, raising concerns for public health. Among the main categories of pollutant measured is PM2.5, which can enter the respiratory system and contribute to a range of illnesses, including cardiovascular disease.

Now, in a new study published in the public health journal Environmental Health Perspectives, researchers from the School of Public Health at Fudan University in Shanghai have demonstrated correlations between PM2.5 pollution and the incidence of particular illnesses.

Researchers spent about two years collecting data in a medium-sized city in northern China, measuring the levels of particulate matter in 23 size categories ranging from 0.25 microns to 10 microns. They then plotted the health conditions of residents in the city against the concentrations of particles of different sizes found in their locations.

Among the key findings was that those areas with larger concentrations of smaller particles showed higher incidences of particular illnesses.

"Our study, based on epidemiological investigation, showed that fine particles in the air measuring between 0.25 to 0.5 microns in diameter have a closer relationship to human health, especially an increased risk of cardiovascular diseases," said Kan Haidong, a professor at the School of Public Health at Fudan University.

The fine particles measuring between 0.25 to 0.5 microns in diameter accounted for about 90 percent of the total number of particles found in the air during the study.

Kan said the smaller the particle, the higher the concentration in any given volume of air and so the greater the number of particles coming into contact with tissues inside the human body.

"Besides that, there may also be a relationship with the settlement of particles of different diameters in the lower respiratory tract." Kan said.

Kan said the smaller particles can also pass through the blood-air barrier in the lungs, entering the blood as toxins, and causing cardiovascular disease. Larger particles are not able to pass through the blood-air barrier so easily. He also said that smaller particles in the body can harm the regulation of the human nervous system.

Among the conclusions of the research is that the smaller the particle size, the more danger the pollution poses to public health, suggesting that more research is needed on PM1 pollution — particles of 1 micron or less in diameter.

"The significance of the study is that it has provided a new direction for the prevention and control of atmospheric pollution," Kan said. "What we need to focus on is particles of smaller sizes, rather than PM2.5."

Some scientists have already suggested more studies on PM1 pollution, citing its potential role in causing illness on a large scale.

"In Shanghai, for example, about 80 to 90 percent of the mass concentration of the city's PM2.5 is PM1. So it would be more effective to carry out studies on PM1 than PM2.5," said Yang Xin, professor at the Department of Environmental Science and Engineering at Fudan University.

PM2.5 is the main category of pollution monitored by government departments.

Yang said he has already approached government departments on the environment and related fields to suggest monitoring of PM1 levels, but he has yet to receive a response.