Previous research by Lee and his colleagues showed that UHI in the U.S. and Canada appears to be driven by a lack of vegetation, especially trees, which are highly effective in dissipating heat through convection. But when they attempted to replicate their experiment in China, the model performed poorly.
At first they thought it was due to the structure of Chinese cities, where there is more vertical stacking as opposed to the sprawling nature of cities in the U.S. Instead, they found a strong correlation between the amount of haze and an increase in heat: cities with more haze pollution had an amplified urban heat island effect.
Even more surprising, they found the greatest UHI in midwestern and northwestern small to mid-sized cities, not in the massive cities located along China’s east coast.
China’s semiarid midwestern and northwestern cities have more large aerosol particles due to road dust and coal combustion that create a thick haze layer and result in a net warming of about one-degree Celsius. Lee even speculates that stir-fry cooking contributes to the UHI.
The study also reveals the ways in which local factors can affect the spatial patterning of UHI. For example, although many parts of the U.S. have air pollution problems that affect respiratory health, researchers couldn’t find a correlation between UHI and haze in the U.S., possibly because aerosol particles here are too small to create a warming effect. Here, the highest UHI is found in wet climates — especially southeastern cities such as Atlanta — posing public health risks and management challenges for city administrators in the face of climate change.