<p>Most locations in the US don't see high concentrations of pollutants like NO<sub>2</sub> and CO anymore.  They are largely no longer an air quality problem and air is "Good" in regards to those pollutants.  Especially during "lockdown", when traffic is light.  This is largely thanks to tailpipe emissions standards for vehicles and a much more fuel efficient fleet. On the other hand, PM2.5 has multiple sources that cause high concentrations, and we are much more likely to see the AQI vary beyond "Good" PM2.5 (e.g. outdoor fires, wood-stoves, secondary aerosol formation).  </p>

<p>The AQI is based on health-based evidence, with a different concentration threshold for each pollutant.  These are all put onto the AQI scale for simple communication to the public. If concentrations of NO2 had reached levels of the NAAQS, then you would see your graph plot into those AQI levels (note NO<sub>2</sub> doesn't go as far up in "AQI" values as PM2.5 on your graph because those NO<sub>2</sub> concentrations were never detected by the monitor).  </p>

<p>The National Ambient Air Quality Standard (NAAQS) for nitrogen dioxide (NO<sub>2</sub>) is a 1-hour NO<sub>2</sub> standard of 100 parts per billion (ppb). See <a href="https://www3.epa.gov/airnow/no2.pdf" rel="nofollow noreferrer">https://www3.epa.gov/airnow/no2.pdf</a> and page 2 here: <a href="http://njaqinow.net/App_Files/2016/AQI%202016.pdf" rel="nofollow noreferrer">http://njaqinow.net/App_Files/2016/AQI%202016.pdf</a> which has the break levels for each pollutant, shown below:</p>

<p><a href="https://i.sstatic.net/HP4Ez.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/HP4Ez.png" alt="enter image description here"></a></p>

CC BY-SA 4.0
2020-05-30T19:03:39.990Z
2020-05-31T18:48:42.647Z
2020-05-31T18:48:42.647Z
f.thorpe
<p>I am comparing NO2 and PM2.5 levels in the pre-2020 Jan-April and 2020 Jan-April (representing air quality during lockdown and under no-lockdown conditions).</p>

<p>The data was from the aqicn website (<a href="https://aqicn.org/data-platform/covid19/" rel="nofollow noreferrer">https://aqicn.org/data-platform/covid19/</a>). The data is not raw concentrations, it is converted into the US EPA standard, which I <strong>believe</strong> is represented as AQI values.</p>

<p>Can someone please explain why with PM2.5, the data reaches from 'Good' to 'Hazardous', whereas the NO2 is only within the 'Good' bracket. 
I'm hoping it is because PM2.5 is more  harmful than NO2? </p>

<p>But if it is because I should be using a different scale for NO2 (e.g., 0-10 = Good, 10-20 = Moderate, etc.) I'd like to know - I haven't been able to find different AQI scales for different pollutants.</p>

<p><a href="https://i.sstatic.net/xRayd.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/xRayd.jpg" alt="PM2.5"></a>
<a href="https://i.sstatic.net/e4pMq.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/e4pMq.jpg" alt="NO2"></a></p>

<air-quality>
How is Air Quality Index relevant to both PM2.5 and NO2
Amelia
# How is Air Quality Index relevant to both PM2.5 and NO2

(Asked by: username_0 on 2020-05-30)

I am comparing NO2 and PM2.5 levels in the pre-2020 Jan-April and 2020 Jan-April (representing air quality during lockdown and under no-lockdown conditions).

The data was from the aqicn website (<https://aqicn.org/data-platform/covid19/>). The data is not raw concentrations, it is converted into the US EPA standard, which I **believe** is represented as AQI values.

Can someone please explain why with PM2.5, the data reaches from 'Good' to 'Hazardous', whereas the NO2 is only within the 'Good' bracket.
I'm hoping it is because PM2.5 is more harmful than NO2?

But if it is because I should be using a different scale for NO2 (e.g., 0-10 = Good, 10-20 = Moderate, etc.) I'd like to know - I haven't been able to find different AQI scales for different pollutants.

[![PM2.5](https://i.sstatic.net/xRayd.jpg)](https://i.sstatic.net/xRayd.jpg)
[![NO2](https://i.sstatic.net/e4pMq.jpg)](https://i.sstatic.net/e4pMq.jpg)

**Tags:** air-quality


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## 1 answers

### Answer by username_1 on 2020-05-30. Score: 2 | Accepted answer

Most locations in the US don't see high concentrations of pollutants like NO2 and CO anymore. They are largely no longer an air quality problem and air is "Good" in regards to those pollutants. Especially during "lockdown", when traffic is light. This is largely thanks to tailpipe emissions standards for vehicles and a much more fuel efficient fleet. On the other hand, PM2.5 has multiple sources that cause high concentrations, and we are much more likely to see the AQI vary beyond "Good" PM2.5 (e.g. outdoor fires, wood-stoves, secondary aerosol formation).

The AQI is based on health-based evidence, with a different concentration threshold for each pollutant. These are all put onto the AQI scale for simple communication to the public. If concentrations of NO2 had reached levels of the NAAQS, then you would see your graph plot into those AQI levels (note NO2 doesn't go as far up in "AQI" values as PM2.5 on your graph because those NO2 concentrations were never detected by the monitor).

The National Ambient Air Quality Standard (NAAQS) for nitrogen dioxide (NO2) is a 1-hour NO2 standard of 100 parts per billion (ppb). See <https://www3.epa.gov/airnow/no2.pdf> and page 2 here: <http://njaqinow.net/App_Files/2016/AQI%202016.pdf> which has the break levels for each pollutant, shown below:

[![enter image description here](https://i.sstatic.net/HP4Ez.png)](https://i.sstatic.net/HP4Ez.png)


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