What Impact Does Rain Have on Delhi Pollution?

When New York Times journalists write about the health impacts that living in Delhi had on their children, Delhites are bound to take any small measure that might reduce the pollution in the air.

The recent rain showers in Delhi got us thinking: What impact does rain have on Delhi air pollution? You might think that the water falling from the sky has a cleansing effect, but is there any data to support this?

Take a look at the chart below, it shows the air quality levels in Delhi as reported by the US Embassy in the city over a 48 hour period. Notice how it rises and falls.

delhi 48 hour air quality

On both days the pollution reaches levels which the US calls Very Unhealthy at the same time each day before rapidly abating down to Moderate levels, as indicated by the red arrows.

So what is causing these sudden dips in air quality? To see if it had anything to do with the rain, we looked at the rain fall for this same time period. The results are plotted on the chart below.


The chart shows that at the exact time there is rain fall, the air quality improves considerably. Although this is anecdotal evidence at best, there is a clear correlation over the 48 hours seen in the chart above that says air pollution in Delhi falls drastically when there is rain.

Maybe the Government can start seeding the clouds to promote rain, but until then, the population needs to rely on air purifiers to at least clean the air in the home and office.