# Which PurpleAir parameters to use for EPA PM2.5 correction? **URL:** \ **Category:** API\ **Created:** [September 19, 2022, 6:49pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072 "2022-09-19T18:49:59Z")\ **Posts on this page:** 11\ **Page:** 1
**Author:** ![adanecito](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/adanecito/32/1218_2.png) [@adanecito](https://community.purpleair.com/u/adanecito)\ **Post date:** [September 19, 2022, 6:49pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/1 "2022-09-19T18:49:59Z")
Hi All, I was directed to read the EPA pdf that contained the correction equation for PM2.5 reading. I created the formula but not sure where to get in the PurpleAir API the needed data. For example for PM2.5 the equation is: PM2.5=0.541_PA\_cf1(avgAB)-0.0618_RH +0.00534\*T +3.634 T or temperature I am assuming we use the the temperature reading from the API PA\_cf1(avgAB) What is that? Is it pm2.5\_cf\_1? RH means relative humidity is that the humidity parameter in the API? I am hoping to just make one API call to get these variables. Any help appreciated! ---
**Author:** ![dwhitemv](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/dwhitemv/32/1508_2.png) [@dwhitemv](https://community.purpleair.com/u/dwhitemv)\ **Post date:** [September 21, 2022, 4:19am UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/2 "2022-09-21T04:19:09Z")
What is your source for that formula? I’ll update the other thread. ---
**Author:** ![adanecito](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/adanecito/32/1218_2.png) [@adanecito](https://community.purpleair.com/u/adanecito)\ **Post date:** [September 21, 2022, 4:35am UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/3 "2022-09-21T04:35:55Z")
Your questions are fine. I got the EPA from the AirNow map. [https://gispub.epa.gov/airnow/?monitors=pm25&contours=none&xmin=-14256862.295991126&xmax=-13214872.726407655&ymin=5865361.713785472&ymax=6342328.770284948](https://gispub.epa.gov/airnow/?monitors=pm25&contours=none&xmin=-14256862.295991126&xmax=-13214872.726407655&ymin=5865361.713785472&ymax=6342328.770284948) ---
**Author:** ![adanecito](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/adanecito/32/1218_2.png) [@adanecito](https://community.purpleair.com/u/adanecito)\ **Post date:** [September 21, 2022, 4:36am UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/4 "2022-09-21T04:36:59Z")
The formula I got from an EPA document. It was mentioned on another thread. ---
**Author:** ![adanecito](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/adanecito/32/1218_2.png) [@adanecito](https://community.purpleair.com/u/adanecito)\ **Post date:** [September 21, 2022, 2:02pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/5 "2022-09-21T14:02:32Z")
Here is the doc where I was sent to get the latest EPA formula. [https://cfpub.epa.gov/si/si\_public\_record\_report.cfm?Lab=CEMM&dirEntryId=354999](https://cfpub.epa.gov/si/si_public_record_report.cfm?Lab=CEMM&dirEntryId=354999) ---
**Author:** ![wzhang](https://avatars.discourse-cdn.com/v4/letter/w/3be4f8/32.png) [@wzhang](https://community.purpleair.com/u/wzhang)\ **Post date:** [September 21, 2022, 8:06pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/6 "2022-09-21T20:06:46Z")
In the EPA document you mentioned. The latest set of equations are: ![image](https://us1.discourse-cdn.com/flex020/uploads/purpleair/original/2X/7/70e525f4313703fa8e46038c7b9b9d42916a3ec1.png) ---
**Author:** ![wzhang](https://avatars.discourse-cdn.com/v4/letter/w/3be4f8/32.png) [@wzhang](https://community.purpleair.com/u/wzhang)\ **Post date:** [September 21, 2022, 8:11pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/7 "2022-09-21T20:11:32Z")
For 1-hour average data, EPA calculated it from rolling 10 minute average following their quality control procedure. ![image](https://us1.discourse-cdn.com/flex020/uploads/purpleair/original/2X/9/9ad721f565b806b64c82042f039becf598197c26.png) ---
**Author:** ![wzhang](https://avatars.discourse-cdn.com/v4/letter/w/3be4f8/32.png) [@wzhang](https://community.purpleair.com/u/wzhang)\ **Post date:** [September 21, 2022, 8:26pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/8 "2022-09-21T20:26:33Z")
Therefore, the PurpleAir parameters used in EPA PM2.5 correction are: humidity : Relative humidity pm2.5\_10minute\_a : channel A of rolling 10 minute average pm2.5\_10minute\_b : channel B of rolling 10 minute average Mare sure the location\_type is 0 so it is an outdoor sensor. for outdoor sensors, pm2.5\_10minute\_a and pm2.5\_10minute\_b are cf\_atm From PurpleAir API web page ([Loading...](https://api.purpleair.com/#api-sensors-get-sensors-data)) ![image](https://us1.discourse-cdn.com/flex020/uploads/purpleair/original/2X/f/fc9a7b3203be83b2afd6a4a2286a14ef9cf3b144.png) ![image](https://us1.discourse-cdn.com/flex020/uploads/purpleair/original/2X/b/b3fe2725d062bff7fb9b27e4ff1605f6701bc1e8.png) ---
**Author:** ![dwhitemv](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/dwhitemv/32/1508_2.png) [@dwhitemv](https://community.purpleair.com/u/dwhitemv)\ **Post date:** [September 26, 2022, 5:50pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/9 "2022-09-26T17:50:34Z")
@adanecito, Reason I was asking was that none of the EPA published formulas have a correction for temperature, but yours (the formula in the top post) does. Man, EPA went off the deep end trying to reverse engineer CF\_ATM. ---
**Author:** ![adanecito](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/adanecito/32/1218_2.png) [@adanecito](https://community.purpleair.com/u/adanecito)\ **Post date:** [September 26, 2022, 6:04pm UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/10 "2022-09-26T18:04:32Z")
I can agree with you. But that is the standard and I believe in standards. ugh. ---
**Author:** ![Lance](https://sea2.discourse-cdn.com/flex020/user_avatar/community.purpleair.com/lance/32/422_2.png) [@Lance](https://community.purpleair.com/u/Lance)\ **Post date:** [October 2, 2022, 2:52am UTC](https://community.purpleair.com/t/which-purpleair-parameters-to-use-for-epa-pm2-5-correction/2072/11 "2022-10-02T02:52:06Z")
There is an improved formula on API. The name is “PM2.5 alt”. The same formula is available for downloading on the PurpleAir mapping page, where it is called “ALT-CF3”. It is based on several published peer-reviewed papers referenced on the mapping page. It’s a good deal simpler than the latest EPA formula.