A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Laboratory evaluation of low-cost PurpleAir PM monitors and in-field correction using co-located portable filter samplers
https://orcid.org/0000-0002-0522-4551
https://orcid.org/0000-0002-7563-9525
Abstract Low-cost aerosol monitors can provide more spatially- and temporally-resolved data on ambient fine particulate matter (PM2.5) concentrations than are available from regulatory monitoring networks; however, concentrations reported by low-cost monitors are sometimes inaccurate. We investigated laboratory- and field-based approaches for calibrating low-cost PurpleAir monitors. First, we investigated the linearity of the PurpleAir response to NIST Urban PM and derived a laboratory-based gravimetric correction factor. Then, we co-located PurpleAirs with portable filter samplers at 15 outdoor sites spanning 3 × 3-km in Fort Collins, CO, USA. We evaluated whether PM2.5 correction factors calculated using ambient relative humidity data improved the accuracy of PurpleAir monitors (relative to reference filter samplers operated at 16.7 L min−1). We also (1) evaluated gravimetric correction factors derived from periodic co-locations with portable filter samplers and (2) compared PM2.5 concentrations measured using portable and reference filter samplers. Both before and after field deployment, a linear model relating NIST Urban PM concentrations reported by a tapered element oscillating microbalance and PurpleAir monitors (“PM2.5 ATM”) had R2 = 99%; however, an F-test identified a significant lack of fit between the model and the data. The laboratory-based correction did not translate to the field. Over a 35-day period, time-averaged ambient PM2.5 concentrations and RHs measured during 72- or 48-h filter samples ranged from 1.5 to 8.3 μg m−3 and 47%–77%, respectively. Corrections calculated using ambient RH data increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference concentration from 24% (for uncorrected measurements) to 66%. Corrections derived from monthly, weekly, and concurrent in-field co-locations with portable filter samplers increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference to 46%, 54%, and 72%. PM2.5 concentrations measured using portable filter samplers were within 20% of the reference for 69% of samples.
Graphical abstract Display Omitted
Highlights The PurpleAir PM2.5 ATM response to NIST Urban PM was approximately 1:1 in the lab. Uncorrected PurpleAir monitors overestimated PM2.5 mass concentrations in the field. Correction for particle growth at elevated relative humidity reduced PurpleAir bias. Periodic correction to co-located filter samples also reduced PurpleAir bias. 72-h PM2.5 (μg m−3) measured by portable and conventional filter samplers agreed.
Laboratory evaluation of low-cost PurpleAir PM monitors and in-field correction using co-located portable filter samplers
https://orcid.org/0000-0002-0522-4551
https://orcid.org/0000-0002-7563-9525
Abstract Low-cost aerosol monitors can provide more spatially- and temporally-resolved data on ambient fine particulate matter (PM2.5) concentrations than are available from regulatory monitoring networks; however, concentrations reported by low-cost monitors are sometimes inaccurate. We investigated laboratory- and field-based approaches for calibrating low-cost PurpleAir monitors. First, we investigated the linearity of the PurpleAir response to NIST Urban PM and derived a laboratory-based gravimetric correction factor. Then, we co-located PurpleAirs with portable filter samplers at 15 outdoor sites spanning 3 × 3-km in Fort Collins, CO, USA. We evaluated whether PM2.5 correction factors calculated using ambient relative humidity data improved the accuracy of PurpleAir monitors (relative to reference filter samplers operated at 16.7 L min−1). We also (1) evaluated gravimetric correction factors derived from periodic co-locations with portable filter samplers and (2) compared PM2.5 concentrations measured using portable and reference filter samplers. Both before and after field deployment, a linear model relating NIST Urban PM concentrations reported by a tapered element oscillating microbalance and PurpleAir monitors (“PM2.5 ATM”) had R2 = 99%; however, an F-test identified a significant lack of fit between the model and the data. The laboratory-based correction did not translate to the field. Over a 35-day period, time-averaged ambient PM2.5 concentrations and RHs measured during 72- or 48-h filter samples ranged from 1.5 to 8.3 μg m−3 and 47%–77%, respectively. Corrections calculated using ambient RH data increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference concentration from 24% (for uncorrected measurements) to 66%. Corrections derived from monthly, weekly, and concurrent in-field co-locations with portable filter samplers increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference to 46%, 54%, and 72%. PM2.5 concentrations measured using portable filter samplers were within 20% of the reference for 69% of samples.
Graphical abstract Display Omitted
Highlights The PurpleAir PM2.5 ATM response to NIST Urban PM was approximately 1:1 in the lab. Uncorrected PurpleAir monitors overestimated PM2.5 mass concentrations in the field. Correction for particle growth at elevated relative humidity reduced PurpleAir bias. Periodic correction to co-located filter samples also reduced PurpleAir bias. 72-h PM2.5 (μg m−3) measured by portable and conventional filter samplers agreed.
Laboratory evaluation of low-cost PurpleAir PM monitors and in-field correction using co-located portable filter samplers
https://orcid.org/0000-0002-0522-4551
https://orcid.org/0000-0002-7563-9525
Abstract Low-cost aerosol monitors can provide more spatially- and temporally-resolved data on ambient fine particulate matter (PM2.5) concentrations than are available from regulatory monitoring networks; however, concentrations reported by low-cost monitors are sometimes inaccurate. We investigated laboratory- and field-based approaches for calibrating low-cost PurpleAir monitors. First, we investigated the linearity of the PurpleAir response to NIST Urban PM and derived a laboratory-based gravimetric correction factor. Then, we co-located PurpleAirs with portable filter samplers at 15 outdoor sites spanning 3 × 3-km in Fort Collins, CO, USA. We evaluated whether PM2.5 correction factors calculated using ambient relative humidity data improved the accuracy of PurpleAir monitors (relative to reference filter samplers operated at 16.7 L min−1). We also (1) evaluated gravimetric correction factors derived from periodic co-locations with portable filter samplers and (2) compared PM2.5 concentrations measured using portable and reference filter samplers. Both before and after field deployment, a linear model relating NIST Urban PM concentrations reported by a tapered element oscillating microbalance and PurpleAir monitors (“PM2.5 ATM”) had R2 = 99%; however, an F-test identified a significant lack of fit between the model and the data. The laboratory-based correction did not translate to the field. Over a 35-day period, time-averaged ambient PM2.5 concentrations and RHs measured during 72- or 48-h filter samples ranged from 1.5 to 8.3 μg m−3 and 47%–77%, respectively. Corrections calculated using ambient RH data increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference concentration from 24% (for uncorrected measurements) to 66%. Corrections derived from monthly, weekly, and concurrent in-field co-locations with portable filter samplers increased the fraction of time-averaged PurpleAir PM2.5 concentrations that were within 20% of the reference to 46%, 54%, and 72%. PM2.5 concentrations measured using portable filter samplers were within 20% of the reference for 69% of samples.
Graphical abstract Display Omitted
Highlights The PurpleAir PM2.5 ATM response to NIST Urban PM was approximately 1:1 in the lab. Uncorrected PurpleAir monitors overestimated PM2.5 mass concentrations in the field. Correction for particle growth at elevated relative humidity reduced PurpleAir bias. Periodic correction to co-located filter samples also reduced PurpleAir bias. 72-h PM2.5 (μg m−3) measured by portable and conventional filter samplers agreed.
Laboratory evaluation of low-cost PurpleAir PM monitors and in-field correction using co-located portable filter samplers
Tryner, Jessica (author) / L'Orange, Christian (author) / Mehaffy, John (author) / Miller-Lionberg, Daniel (author) / Hofstetter, Josephine C. (author) / Wilson, Ander (author) / Volckens, John (author)
Atmospheric Environment ; 220
2019-10-20
Article (Journal)
Electronic Resource
English
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