Technical note: Understanding the effect of COVID-19 on particle pollution using a low-cost sensor network

Abstract

The 2020 coronavirus pandemic and the following quarantine measures have led to significant changes in daily life worldwide. Preliminary research indicates that air quality has improved in many urban areas as a result of these measures. This study takes a neighborhood-scale approach to quantifying this change in pollution. Using data from a network of citizen-hosted, low-cost particulate matter (PM) sensors, called Air Quality & yoU (AQ&U), we obtained high-spatial resolution measurements compared to the relatively sparse state monitoring stations. We compared monthly average estimated PM 2.5 concentrations from February 11 to May 11, 2019 at 71 unique locations in Salt Lake County, UT, USA with the same (71) sensors’ measurements during the same timeframe in 2020. A paired t -test showed significant reductions (71.1% and 21.3%) in estimated monthly PM 2.5 concentrations from 2019 to 2020 for the periods from March 11-April 10 and April 11-May 10, respectively. The March time period corresponded to the most stringent COVID-19 related restrictions in this region. Significant decreases in PM 2.5 were also reported by state monitoring sites during March (p < 0.001 compared to the previous 5-year average). While we observed decreases in PM 2.5 concentrations across the valley in 2020, it is important to note that the PM 2.5 concentrations did not improve equally in all locations. We observed the greatest reductions at lower elevation, more urbanized areas, likely because of the already low levels of PM 2.5 at the higher elevation, more residential areas, which were generally below 2 μg/m 3 in both 2019 and 2020. Although many of measurements during March and April were near or below the estimated detection limit of the low-cost PM sensors and the federal equivalent measurements, every low-cost sensor (51) showed a reduction in PM 2.5 concentration in March of 2020 compared to 2019. These results suggest that the air quality improvement seen after March 11, 2020 is due to quarantine measures reducing traffic and decreasing pollutant emissions in the region.

A low-cost monitor for simultaneous measurement of fine particulate matter and aerosol optical depth – Part 3: Automation and design improvements

“…Satellite remote sensing, supplemented with data from surface measurements and chemical transport models (CTMs), represents the state of the art for global PM 2.5 monitoring at relatively high temporal and spatial resolution (van Donkelaar et al, , 2019Hammer et al, 2020;Lee, 2020). Measurements from satellite instruments, such as the Moderate Resolution Imaging Spectrometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR) (Salomonson et al, 1989;Diner et al, 1998), are used to estimate surface-level PM 2.5 concentrations (e.g Liu et al, 2005), which, in turn, have facilitated research into the health effects associated with PM 2.5 exposure (Brauer et al, 2016;Forouzanfar et al, 2016;Li et al, 2018;Lu et al, 2019). Satellites equipped with aerosol remote sensing instrumentation retrieve aerosol optical depth (AOD), a measure of light extinction in the atmospheric column, which can then be converted to ground-level PM 2.5 using a CTM or statistical relationship (Liu et al, 2005; van Donkelaar et al, 2006van Donkelaar et al, , 2010van Donkelaar et al, , 2012Hammer et al, 2020).…”

“…Networks of low-cost nephelometers (notably the Plantower PMS5003) have been suggested and deployed in large numbers as a means to provide surface PM 2.5 data at a higher spatial density than can be achieved with reference-grade monitors (Lin et al, 2020;Li et al, 2020;Badura et al, 2020;Lu et al, 2021;Chadwick et al, 2021). However, low-cost sensors (or more specifically, the Plantower PMS5003 devices) tend to exhibit measurement bias (Kelly et al, 2017;Zheng et al, 2018;Levy Zamora et al, 2019;Sayahi et al, 2019;Tryner et al, 2020), requiring correction relative to reference monitors (Ford et al, 2019;Wendt et al, 2019).…”

The impact of COVID-19 lockdown on air pollution in Europe and North America: a systematic review

“…As one example, Chadwick et al . 18 found major reductions of up to 71% in the period 11 March to 10 April 2020, which were periods of intense quarantine. Greater reductions were seen in lower elevation and more urbanized areas.…”

Role of vehicular emissions in urban air quality: The COVID-19 lockdown experiment

“…Another source of measurements are the high spatio-temporal resolution datasets collected through low-cost sensor network and mobile sensing strategies, which are becoming increasingly popular for capturing intra-urban air quality gradients ( Motlagh et al, 2021 ; Llaguno-Munitxa & Bou-Zeid 2020; Yang and Bou-Zeid, 2019 , Apte et al, 2017 ). Various studies have made use of these datasets and reported that lockdown measures have revealed heterogeneous drops of air pollution at the neighborhood level and have been associated with reference traffic volume reductions ( Chadwick et al, 2021 ; Wang et al, 2021; Hudda et al, 2020 ).…”