Haze Pollution and Hotter Cities in China and the US are Not Created Equal

Chinese and US cities have both been warming up, but the composition of their haze pollution and underlying reasons for the temperature increase differ.

A study from Yale School of Forestry & Environmental Studies published in the journal Nature Communications on Tuesday provided some interesting insights into the phenomenon of cities experiencing hotter temperatures than surrounding areas, called the urban heat island effect (UHI). Not all pollution particles making up the city haze are responsible for the heat.

Fine particles actually help keep the city cool by blocking sunlight, though they're responsible for a host of health problems including asthma and increased risk of cancer and heart disease. Larger aerosol particles are the culprits in UHI because they absorb and radiate heat -- they are a health hazard as well.

"When people talk about aerosols, particle size matters a lot." senior author of the study and professor of meteorology at Yale School of F&ES Xuhui Lee said.

Large aerosol particles come from dust, coal, sand and cooking and are largely absent from city haze found in the US. East coast metropolises in China also have fewer large aerosol particles than cities in the middle and west of China.

This research compounds the fact that air pollution must be reduced for the sake of health, environment and comfort.

"Cleaning up has a co-benefit. It helps improve human health, but it also helps to cool the local climate," Lee continued.

Previous research indicated a lack of vegetation played a part in the rising temperatures of US cities. Scientists had thought insufficient vegetation was also to blame for UHI in China, but were unable to replicate the US results.

Comparisons between countries are helpful in identifying or ruling out the roles of different factors in climate change. Multi pronged city haze management plans of reducing both types of pollutant particles and increasing vegetation will provide a widespread benefit to the world's cities and their inhabitants.