Self-Protection from Smog

Inequality in pollution exposure between low- and high-income households.

Research has previously shown that air pollution is damaging to our health, productivity, and education. Apart from government regulations to reduce emissions, individuals can invest in protective equipment, such as masks and air filters, to reduce their exposure to air pollution.

Do people tend to buy more masks and air filters when air quality is bad? 

Do spending patterns differ between low- and high-income households? 

A comparison of two air pollution protection products


Air filters may cost more than masks, but they are much more effective at filtering out air pollution. However, not everyone can afford to invest in more expensive air filters, and this may lead to inequality in pollution exposure.

We looked at 34 cities using sales data from, China's largest online shopping platform

To understand people’s spending response to bad air quality, we compared daily sales data from Nov 1, 2013 to Jan 31, 2014 to PM2.5 concentration data and daily pollution alerts from China’s Ministry of Environmental Protection (MEP).

To investigate spending differences between low and high-income households, we collected monthly sales data from April 2013 to April 2014 for low, medium, and high-income groups.

People invest more in masks and filters when air pollution is bad

People respond to both government pollution alerts and actual PM2.5 concentration levels by buying more masks and air filters.


People's spending response increases as polluted levels get worse. People tend to buy more masks than air filters.

People spend more on masks than air filters on badly polluted days, possibly due to the cheaper cost of masks. 


Inequality in air pollution exposure

People with higher incomes invest more in smog protection, especially in more expensive and effective products. Whereas, individuals in the low-income group buy significantly more masks but not air filters.

High-income people are about 3x more likely to purchase air filters than low-income people.


Low-income people are about 2.5x more likely to purchase masks than high-income people.

High and medium-income people tend to purchase more air filters, which are more expensive but more effective, compared to low-income people.

This difference in cost and effectiveness of protection equipment and spending between low and high income groups means that there is inequality in air pollution exposure which impacts the quality of life in Chinese cities.

Given widespread concerns about the consequences of income inequality in both the United States and China, it remains an important research topic to study how and why different income levels are exposed to different air pollution levels.



Web and Visuals

Siqi Zheng

MIT China Future City Lab, Department of Urban Studies and Planning, 

Center for Real Estate

Cong Sun

Shanghai University of Economics and Finance

Matthew Kahn

University of Southern California and NBER

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