What is the Difference Between CF=1, ATM, and ALT?

Data API
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I’d be interested in what results were obtained for mean PM.5 comparing the two algorithms against the US EPA values. I would expect the CF_ATM algorithm would overpredict the FEM values by say 30-50%, whereas the pm2.5 alt or ALT-CF3 might underpredict by about 10%. This is because we found 3.4 may be a better calibration factor than the 3.0 that is used in the PurpleAir API.

Have you tried to determine the LOD of the two algorithms? My evidence shows that the LOD of the CF_1 algorithm (which would be the same as that for the CF_ATM algorithm) is considerably higher than that for the ALT-CF3 algorithm. The result for indoor air values (well below outdoor air values by almost a factor of 2) was that a very high percentage of CF_1 samples were below the LOD, and even resulted in zero 20% of the time…

Have you considered doing the same analysis for indoor air? This was done by my group for 2017-2021 in west Coast states only. Results are very strongly affected by the algorithm used, with 20% or more of the CF_1 (and therefore the CF_ATM) values equalling zero. It was also done for 2020-2021 by LBNL group (Engelberg (sp?) et al., PNAS December 2023. The indoor air of course has a far higher effect on potential total exposure (and therefore health effects) than do outdoor values.

Do you have an institution? My email is as below in the signature section. Feel free to use that.

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Masoud–

I now see that my attachments (four papers) were rejected by the PurpleAir Community email.
So here is list of recent papers about 10 of which deal with things of interest to you.

  1. Wallace, L. (2023a). Cracking the code—Matching a proprietary algorithm for a low-cost sensor measuring PM1 and PM2.5. Science of the Total Environment 893.164874. https://www.researchgate.net/publication/373512209_Cracking_the_Code–final_manuscript

  2. Wallace, L. (2023b). Testing a New “Decrypted” Algorithm for Plantower Sensors Measuring PM2.5: Comparison with an Alternative Algorithm. Algorithms 2023, 16, 392. https://doi.org/10.3390/a16080392

  3. Wallace, L.; Zhao, T. (2023). Spatial Variation of PM2.5 Indoors and Outdoors: Results from 261 Regulatory Monitors Compared to 14,000 Low-Cost Monitors in Three Western States over 4.7 Years. Sensors 23, 4387. https://doi.org/10.3390/s23094387 .

  4. Wallace, L.A., Ott, W.R. (2023). Long-term indoor-outdoor PM2.5 measurements using
    PurpleAir sensors: an improved method of calculating indoor-generated and outdoor-infiltrated contributions to potential indoor exposure. Sensors 2023, 23(3), 1160. https://www.mdpi.com/1424-8220/23/3/1160 .

  5. Ott, W.R. L.A. Wallace, K.-C. Cheng, et al. (2022), Measuring PM2.5 concentrations from secondhand tobacco vs. marijuana smoke in 9 rooms of a detached 2-story house, Science of the Total Environment https://doi.org/10.1016/j.scitotenv.2022.158244

  6. Wallace, L.A., Zhao, T., Klepeis, N.R. (2022) Indoor contribution to PM2.5 exposure using all PurpleAir sites in Washington, Oregon, and California.Indoor Air 32: (9) 13105. https://onlinelibrary.wiley.com/doi/abs/10.1111/ina.13105.

  7. Wallace, L. Zhao, T. and Klepeis, N.E…(2022) Calibration of PurpleAir PA-I and PA-II monitors using daily mean PM2.5 concentrations measured in California, Washington, and Oregon from 2017 to 2021. Sensors 2022, 22, 4741. [https://doi.org/10.3390/ s22134741](https://doi.org/10.3390/
    s22134741) https://pubmed.ncbi.nlm.nih.gov/35808235/

  8. Wallace, L.(2022) Intercomparison of PurpleAir Sensor Performance over Three Years Indoors and Outdoors at a Home: Bias, Precision, and Limit of Detection Using an Improved Algorithm for Calculating PM2.5. Sensors 2022, 22, 2755. https://doi.org/10.3390/s22072755

  9. Cheng, K-C; Ott, W.R.; Wallace L.A.; Zhu. Y.; Hildemann, L. PM2.5 exposure close to marijuana smoking and vaping: A case study in residential indoor and outdoor settings. Science of The Total Environment, 802 (2022) 149897, ISSN 0048-9697, https://doi.org/10.1016/j.scitotenv.2021.149897 .

https://www.sciencedirect.com/science/article/pii/S004896972104972X

  1. Wallace, L., Bi, J., Ott, W.R., Sarnat, J.A. and Liu, Y. (2021) Calibration of low-cost PurpleAir outdoor monitors using an improved method of calculating PM2.5. Atmospheric Environment, 256 (2021) 118432. https//doi.org/10.1016/j.atmosenviron.2021.118432 https://www.sciencedirect.com/science/article/abs/pii/S135223102100251X

  2. Sun, L. and Wallace, L.A. (2021) Residential cooking and use of kitchen ventilation: The impact on exposure, Journal of the Air & Waste Management Association. https://www.tandfonline.com/doi/full/10.1080/10962247.2020.1823525

12. Wallace, L.A., Ott, W.R., Zhao, T., Cheng, K-C, and Hildemann, L.M. 2021 Method for estimating the volatility of aerosols using the Piezobalance: examples from vaping e-cigarette and marijuana liquids. Atmospheric Environment Volume 253, 15 May 2021, 118379. https://doi.org/10.1016/j.atmosenv.2021.118379

  1. Bi, J., Wallace, L., Sarnat, J.A. and Liu, Y. (2021). Characterizing outdoor infiltration and indoor contribution of PM2.5 with citizen-based low-cost monitoring data. *Environmental Pollution 276:*116793. https://pubmed.ncbi.nlm.nih.gov/33631689/

  2. Ott, W.R., Zhao, T., Cheng, K-C, Wallace, L.A., and Hildemann, L.M. (2021). Measuring indoor fine particle concentrations, emission rates, and decay rates from cannabis use in a residence. Atmospheric Environment. https://doi.org/10.1016/j.aeaoa.2021.100106

  3. Wallace, L., Ott, W., Zhao, T., Cheng, K-C, and Hildemann, L. (2020). Secondhand exposure from vaping marijuana: Concentrations, emissions, and exposures determined using both research-grade and low-cost monitors, Atmospheric Environment X, https://doi.org/10.1016/j.aeaoa.2020.100093 (Accessed 11/19/20)

  4. Zhao, T., Cheng, K-C, Ott, W.R., Wallace L.A., and Hildemann, L.M. (2020) Characteristics of secondhand cannabis smoke from common smoking methods: calibration factor, emission rate, and particle removal rate. Atmospheric Environment. https://doi.org/10.1016/j.atmosenv.2020.117731 (Accessed 11/19/20)

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Thanks again for sharing the materials.