Did Delhi’s Air Pollution Drop 25% in 2019? What the Data Says

Bike Pollution Mask India

The Delhi government and Delhi Chief minister Arvind Kejriwal announced Delhi’s air pollution was down 25% in 2016-2018 compared to 2012-2014.

 

Delhi's air pollution is down by 25%

 

Yet there is doubt. Thewire.in, for one, expressed skepticism about this claim.

 

Delhi government pollution claim

As data-driven nerds, we wanted to let the numbers answer this question. So we dug into the Delhi PM2.5 data to see if this claim by the Delhi government was true and to see if Delhiites are really breathing cleaner air in 2019.

 

Delhi PM2.5 2015-2018

We used data available from the US Embassy to analyze Delhi’s pollution over the past 5 years. Unfortunately, the data only goes back to 2015, so we can’t test the claim back to 2012. However, there’s been no clear improvement since 2015.

 

Delhi average PM2.5 air pollution 2015 to 2018

In 2017, Delhi was 2 micrograms above 2015. In 2018, Delhi was 3 micrograms lower. Thus, the data seems to be saying Delhi’s air has seen “more of the same” for the last four years.

2019: Delhi’s PM2.5 Drops 25%

Has air gotten any better in 2019? If we compare 2019 so far (January 1st, 2019 to October 1st, 2019) to the 2018 average, PM2.5 has actually dropped 25% in 2019!

 

Delhi 2018 PM2.5 level vs 2019 YTD levels

 

Unfortunately, this is misleading. This data is comparing the whole of 2018’s levels to just the first 9 months of 2019.

 

Data shows that pollutions levels are worst during the last 3 months of every year. That’s from crop burning, people building fires for heat, and less air mixing in the winter.

Delhi 2018 PM2.5 levels by month

 

We always expect the first 9 months of any year to have lower average PM2.5, and then the last 3 months to increase that average.

Analysis of Delhi’s 2018 PM2.5 vs. 2019

However, if we compare Delhi’s PM2.5 for the first 9 months of 2018 with the first 9 months of 2019, we get a completely different answer.

Delhi 2018 PM2.5 levels vs. 2019 levels

When correctly adjusted for seasonality, Delhi’s 2019 PM2.5 dropped just 4% from 2018. That a paltry 3 micrograms–well within the range of random fluctuations.

 

Delhi 2019 PM2.5: Bottom Line

For the first 9 months of 2019, Delhi’s PM2.5 dropped 4%. Back to 2015, Delhi’s PM2.5 is mostly flat. Thus, Delhi’s air has seen little improvement over the last four years.

Either way, Delhi’s air pollution levels are still dangerously high. The 2019 average of 80µg/m3 so far is 8 times higher than the WHO’s annual limit.

 

Delhi's air pollution

Open Data

To help people get an idea of how Delhi’s PM2.5 has changed over the past 5 years, we’ve created a year by year and month by month table, breaking down the data. Data is openly available from the US Embassy in Delhi.

 

Delhi monthly annual PM2.5 2016-2019
Note: In the main analysis, we seasonally adjusted 2015 data to account for the fact that January data is unavailable.

 

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