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Evaluation and Field Calibration of a Low-cost Ozone Monitor at a Regulatory Urban Monitoring Station

Category: Urban Air Quality

Accepted Manuscripts
DOI: 10.4209/aaqr.2018.02.0056
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Mauro Masiol1, Stefania Squizzato1, David Chalupa2, David Q. Rich1,2, Philip K. Hopke 1,3

  • 1 Department of Public Health Sciences, University of Rochester Medical Center, Rochester, NY 14642, USA
  • 2 Department of Environmental Medicine, University of Rochester Medical Center, Rochester, NY 14642, USA
  • 3 Center for Air Resources Engineering and Science, Clarkson University, Potsdam, NY 13699, USA

Highlights

A low-cost ozone monitor & FEM were located at an urban air quality station.
A 12% overestimation was found with respect to FEM analyzer.
Differences in response were investigated using air quality and weather data.
Three corrections are proposed to produce “FEM-like” ozone concentrations.


Abstract

The performance of a low cost ozone monitor (Aeroqual Series 500 portable gas monitors coupled with a metal oxide sensor for ozone; model OZL) was assessed under field conditions. Ten ozone monitors were initially calibrated in clean-air laboratory conditions and tested at controlled ozone concentrations of 5 to 100 ppb. Results showed good linearity and fast response with respect to a conventional research-grade ozone monitor. One monitor was then co-located at a regulatory air quality monitoring station that uses a U.S. federal equivalent method (FEM) ozone analyzer. Raw data from the Aeroqual monitor collected over 4 months (June–October) at a 10-minute time-resolution, showed good agreement (r2 = 0.83) with the FEM values but with an overestimation of ~12%. Data were averaged to different time resolutions; 1 h time averaged concentrations showed the best fit with the FEM results (r2 = 0.87). An analysis of the ratio of FEM/monitor concentrations against chemical and meteorological variables suggested the potential of interferences due to temperature, relative humidity, nitrogen oxides, and volatile organic compounds. Three correction models using temperature, humidity, and nitrogen dioxide (NO2) were then tested to better relate the monitor concentrations to the FEM values. Temperature and humidity are two variables commonly available (or easily measurable) at sampling sites. The model (#3) that added NO2 did not provide a substantial improvement in the fit. Thus, the proposed models with only temperature and humidity can be easily adopted and adapted by any user. The corrected data explained up to 91% of the variance and showed statistically significant improvement of the goodness of fits as well as decreased influence of the interfering variables on the diurnal and weekly patterns. The correction models were also able to lower the effect of seasonal temperature changes, allowing the use of the monitors over long-term sampling campaigns. This study demonstrated that the Aeroqual ozone monitors can return “FEM-like” concentrations after appropriate corrections. Therefore, data provided by a network of monitors could determine the intra-urban spatial variations in ozone concentrations. These results suggest that these monitors could provide more accurate human exposure assessments and thereby reduce exposure misclassification and its resulting bias in epidemiological studies.

Keywords

Semiconductor gas sensor Tropospheric ozone Urban air pollution Air pollution exposure


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