The reason I entered the solar industry in 2013 was because I genuinely care about what we are doing to our planet. Working at a diesel engine company, ironically, got me well acquainted with and concerned about NOx, SOx and particulate matter.

Now in Delhi, the Odd-Even debate has brought the particulate matter and air quality conversation to the common man’s dining table. Unfortunately, the debate is being carried out without a sophisticated look at real data. While I swear by the adage that ‘We trust in God, everyone else bring data’, it is also important to realize that data not analyzed properly is like a knife in a child’s hand.

The number below shows the real time air quality index in Delhi.

Well read and educated people are blindly comparing spot air quality data as from above for period end of Dec ’15 to mid of Jan ’16 and declaring Odd-Even to be a failure. Firstly the correct comparison will be between Jan ’15 and Jan ’16 corrected for temp, wind speed etc- factors that have a part to play in PM 2.5.

Diverting from our regular hardcore solar fare, I decided to share some real air quality measurement numbers. The first step will be to understand the seasonal nature of particulate matter.

Delhi PM2.5 levels for 2013, 2014 and 2015

Data Source: Hourly PM2.5 data collected at the American embassy in Delhi. Note this is raw data and not AQI.

Method: I have averaged the hourly data for each month- i.e. taken averages for 9:00 AM for each day in Jan and so on and graphed the monthly averages for the years 2013, 2014 and 2015.

Key Takeaways: 

  1. As can be seen from the graphs, particulate matter concentration, measured in micrograms per cubic meter, varies dramatically from season to season and hour to hour.
  2. From 2013, you can see a clear seasonal divide. The monsoon and pre-monsoon months of June, July, August and September are nicely clustered at the bottom of the graph- PM2.5 levels are least in these months with little intra day variation. This is logical considering that particulate matter settles down with rain.
  3. The winter months of Nov, Dec and Jan are worst in terms of PM2.5 and the variation within days is also extreme. This again makes sense because with cold temperatures and without any winds, the particles would get concentrated and not disperse. Note how the particulate matter is higher in the mornings and evenings in the winter months when temperatures are lower- a key reason why your outdoor morning jog will do you more harm than good!
  4. The summer months of March, April, May and the transitional months of Feb and Oct are clustered in the middle.

Over the next few articles in this series, I will try to study the impact of Odd and Even on AQI. While it may not be the only activity that will counter this health hazard, it is certainly the much needed first of many. I will also try to trace how the mass scale adoption of solar power will help the environment.

Looking forward to your question and comments!