Tuesday, August 28

What makes the difference in day to day air quality?

Yesterday and today are nearly identical end-of-summer days in Pittsburgh. In terms of weather, temperature, and wind, they were cut from the same mold. Yet the air quality index is significantly different from yesterday to today. Neither day is as awful as the orange action days from last week... What makes the difference?

It rained last evening. It was intensely foggy this morning. It is a Tuesday and therefore traffic patterns and weight might vary. But scientifically, what makes the difference?

Tuesday, August 28
Monday, August 27

I wish I knew.

Unfortunately, it's not as simple as looking at the numbers and doing simple math--a particulate matter pollution rate at 58 today (8/28) from a nice low 23 yesterday (8/27) means little to us non-scientist types except that the EPA has done the math and assigned a ranking to the level of pollution present in the air (seeing today as more hazardous because of a higher rate of PM). The National Ambient Air Quality Standards (NAAQS) lists primary and secondary standards--primary for sensitive populations and secondary for the general public welfare.

There's some serious atmospheric science involved with these calculations and the regulations that apply, and I hope to understand more as I continue to read about them, but for now I'll take the AQI for what it's worth and adjust accordingly.


  1. The AQI forecasting is a bit of an art, like forecasting the temperature and chance of rain. You're on the right track, considering the rain, the temps, etc. Forecasters also look at macro-level events--high or low pressure systems several states away. Rain in Indiana can mean less PM for us later, even if it's sunny in PA, for example.

    Sean Nolan, the guy that makes forecasts for PA, gives a very detailed explanation of his reasoning. Check out the right-hand sidebar (after searching on your zip code) on the airnow.gov site for all the meteorological info you need.

    And please, please check out our Athletes United for Healthy Air campaign...you'd be a great spokeswoman! http://gasp-pgh.org/projects/au/

  2. Hi Jamin--thanks for the comment! That's fantastic information. It's good to know I'm on the right track, and I appreciate the resources so I can learn more about this. And I'll definitely check out the campaign you recommended. Thanks for the tip!


Talk to me! Leave a comment and let's chat.