Monday, August 9, 2021

Why is the dot grey? And other fun facts about the smoke map!

The fire and smoke map at the top of this page is a great tool to check current air quality conditions. Clicking on a site gives you information about current conditions, short-term PM2.5 trends, and monitoring site information. You can also see locations of active fires and smoke plumes. Below are a few common questions about the map; let us know if we missed anything in the comments!

What do the different markers on the map indicate?

Circles are permanent monitors, operated by state, local, and tribal air quality professionals. Triangles are temporary monitors, and the squares are privately owned low-cost sensors from Purple Air, with EPA’s correction equation applied.

Why is the dot at my local air monitor grey?

There are a few different reasons why your local air quality monitor is grey:

  •         We have lost communications with the monitor and can’t receive data
  •         There isn’t enough data to calculate an air quality index value (due to previous lost communications)
  •         An air monitoring operator is conducting a calibration, quality control check, or maintenance
  •         Quality Assurance personnel are conducting an instrument performance audit

Clicking on a site gives me information about a NowCast AQI. What is a NowCast?

The dots on the map are what EPA refers to as the “NowCast,” which relates current and previous hourly PM2.5 concentrations to the Air Quality Index, resulting in the color scale you see on the map. The NowCast is meant to give you a sense of what precautions you should take NOW, based not just on the most recent reading, but also on what the trends have been. The NowCast uses longer averages during times when air quality is stable and shorter averages when air quality is quickly changing. So, if a new fire starts and air quality is quickly deteriorating, the NowCast would show a higher advisory level than what the most recent reading would indicate (and vice versa when air quality is improving).

You also may notice that the hourly concentrations on the “Recent History” tab are different than the NowCast AQI—again, that’s due to how the NowCast is calculated using multiple hours of data.

Why is the purple air sensor closest to me different from the nearest regulatory monitor?

Low-cost sensors are great tools to assess local air quality conditions. Differences in terrain and meteorological conditions between the regulatory monitors and low-cost sensors can lead to differences. Regulatory air monitors also follow detailed rules in where they are placed, their distance from local sources, and their inlet heights.

Why is the smoke blog map different from other maps?

Many companies and apps report air quality and air quality index values, but in many cases it’s unknown how their Air Quality Index values are calculated or what data is used. It’s a best practice to look to public agency sources for trusted air quality information.

A few other fun facts for your Monday morning:

For your fun air quality instrumentation fact of the day, the figure below shows what it looks like when a spider crawls into a nephelometer, which is used to measure PM2.5 concentrations.

Yes, spiders are everywhere, including in our air quality monitoring instrumentation!

And for the data folks out there, if it seems like it has been an early start to the fire season in the central and eastern regions of the state, you’re not wrong! Ranil mentioned it in an earlier post, and a regional and county breakdown of the number of days spent in each AQI category since 2011 (only including summer data up to today’s date) indicates the same:


1 comment:

  1. I am here for spider data! :D
    Thanks for all the info, plus art. Doesn't get better than that.


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