Air quality in five of India’s major cities saw little improvement in 2018. In short, air quality was flat in Hyderabad year over year, while air quality worsened in Mumbai and Kolkata. Here’s the full data to show you just how bad India’s air quality levels were in 2018:

Worsening air quality in India comes at a time when China is cutting its air pollution. Analysis of 2018 air quality data showed that air quality improved in 14 of China’s 15 major cities.

Air Quality Worsens in Two Major Cities

PM2.5 pollution—particles smaller than 2.5 microns in diameter—was up 17% in Kolkata. Kolkata now surpasses nine times the World Health Organization annual limit.

Mumbai also saw air quality worsen in 2018. Mumbai’s PM2.5 pollution increased increased 15% over 2017.

Famous for its air pollution, Delhi saw air quality improve 5% over 2017. Despite the improvement, Delhi’s air quality still ranks as the worst of these major cities.

In contrast, Chennai ranked as having the cleanest air in 2018. Chennai’s PM2.5 levels averaged less a third of Delhi’s in 2018.

Microscopic Particles in the Air

The analysis is based on PM2.5 pollution, particles smaller than 2.5 microns in diameter that can penetrate deep into the lungs and even enter the bloodstream. Studies have shown that PM2.5 raises blood pressure, inflammation, and rates of heart attacks and strokes.

The analysis uses over 175,000 hourly air quality data points from the US Embassy and consulates in five major Indian cities. This data is open for researchers, although it is limited. It comes from only one pollution sensor in each city, and pollution can vary between neighborhoods.

Read more: See detailed reports on India air quality for Delhi, Kolkata, Chennai, Hyderabad, and Mumbai.

Studies Document Protective Effects of Purifiers, Masks

Despite the harms of PM2.5, studies have found that wearing masks prevents harmful effects on blood pressure and heart rate variability. Similarly, placebo-controlled studies of air purifiers have found that reducing particulate in the home prevents harm to blood pressure, inflammation, and immune response—even among young, healthy twenty-year-olds.

Smart Air is a certified B Corp committed to combating the myths big companies use to artificially inflate the price of clean air. To help people living in polluted cities protect themselves, Smart Air provides empirically backed, no-nonsense purifiers and masks, thereby helping to lower the cost of clean air.