Field calibrations of a low-cost aerosol sensor at a regulatory monitoring site in California

D. M. Holstius, A. Pillarisetti, K. R. Smith, E. Seto
2014 Atmospheric Measurement Techniques Discussions  
Health effects attributed to ambient fine particulate matter (PM 2.5 ) now rank it among the risk factors with the highest health burdens in the world, but existing monitoring infrastructure cannot adequately characterize spatial and temporal variability in urban PM 2.5 concentrations, nor in human population exposures. The development and eval-5 uation of more portable and affordable monitoring instruments based on low-cost sensors may offer a means to supplement and extend existing
more » ... existing infrastructure, increasing the density and coverage of empirical measurements and thereby improving exposure science and control. Here, we report on field calibrations of a custom-built, batteryoperated aerosol monitoring instrument we developed using low-cost, off-the-shelf op-10 tical aerosol sensors. We calibrated our instruments using 1 h and 24 h PM 2.5 data from a class III US EPA Federal Equivalent Method (FEM) PM 2.5 β-attenuation monitor in continuous operation at a regulatory monitoring site in Oakland, California. We observed negligible associations with ambient humidity and temperature; linear corrections were sufficient to explain 60 % of the variance in 1 h reference PM 2.5 data and 15 72 % of the variance in 24 h data. Performance at 1 h integration times was comparable to commercially available optical instruments costing considerably more. These findings warrant further exploration of the circumstances under which this class of aerosol sensors may profitably be deployed to generate improved PM 2.5 datasets. 25 regulatory networks with current technology is hindered by resource constraints, as 606 AMTD 7, 2014 conventional techniques require costly equipment (Wilson et al., 2002) . In the absence of empirical measurements with adequate spatiotemporal resolution, epidemiologic studies have relied upon models to downscale or interpolate available data from satellites, regulatory monitors, land use databases, and emissions inventories (Brauer et al., 2011; Jerrett et al., 2005) . In studies of air pollution exposures and health effects, the 5 resulting exposure misclassification may attenuate or bias estimates of health effect relationships. Coarsely resolved PM 2.5 monitoring data also hinders scientific understanding of fluxes resulting from urban emissions, atmospheric transformations, and transport mechanisms. Finally, the relative lack of affordable instrumentation also inhibits timely, empirical verifications of policy-based interventions to reduce emissions 10 and exposures. Small, inexpensive, and portable devices, relying on newly available off-the-shelf sensors, may greatly improve our capacity to characterize aerosol concentrations with high spatial and temporal resolution and low system cost, especially when many such devices can be deployed concurrently. However, the utility of this approach has not 15 been adequately characterized in field settings. In the remainder of this paper, we show that it is possible to generate useful and accurate estimates of hourly and daily PM 2.5 concentrations at a regulatory monitoring site by combining one such sensor with other low-cost, readily available hardware. Guided by the prior work of Watson, Wilson, Chow and colleagues Watson et al., 1998; Wilson et al., 2002 Wilson 20 and Suh, 1997), who extensively analyzed and discussed issues in the augmentation of the then-current Federal Reference Method (FRM) PM 2.5 network with continuous PM monitors, we concentrate first and foremost on demonstrating a predictive relationship between (a) the output of the sensor and (b) regulatory monitoring data that is widely relied upon in air quality regulation and epidemiology. We note that, given a pre-25 dictive relationship, further work is still required to establish equivalency with PM 2.5 or any other PM concentration metric. Our intention is to demonstrate "proof of concept" in a natural environment of interest, so that the findings and methodology may be 607 AMTD 7, 605-632, 2014 Abstract AMTD 7, 605-632, 2014 Abstract 25 the physical design is shown in Fig. S1, Supplement. The components were easily procured from online electronics retailers with a total materials cost under $200 (USD) per PANDA. We estimate that a minimal variant, relying on a host device (e.g., a computer 609 Abstract 20 611 AMTD 7, 605-632, 2014 Abstract 7, 605-632, 2014
doi:10.5194/amtd-7-605-2014 fatcat:y5hvagngbvbadglizxduqdojwi