A low-cost monitor for simultaneous measurement of fine particulate matter and aerosol optical depth – Part 1: Specifications and testing

Abstract

Globally, fine particulate matter (PM 2.5 ) air pollution is a leading contributor to death, disease, and environmental degradation. Satellite-based measurements of aerosol optical depth (AOD) are used to estimate PM 2.5 concentrations across the world, but the relationship between satelliteestimated AOD and ground-level PM 2.5 is uncertain. Sun photometers measure AOD from the Earth's surface and are often used to improve satellite data; however, referencegrade photometers and PM 2.5 monitors are expensive and rarely co-located. This work presents the development and validation of the aerosol mass and optical depth (AMOD) sampler, an inexpensive and compact device that simultaneously measures PM 2.5 mass and AOD. The AMOD utilizes a low-cost light-scattering sensor in combination with a gravimetric filter measurement to quantify ground-level PM 2.5 . Aerosol optical depth is measured using optically filtered photodiodes at four discrete wavelengths. Field validation studies revealed agreement within 10 % for AOD values measured between co-located AMOD and AErosol RObotics NETwork (AERONET) monitors and for PM 2.5 mass measured between co-located AMOD and EPA Federal Equivalent Method (FEM) monitors. These results demonstrate that the AMOD can quantify AOD and PM 2.5 accurately at a fraction of the cost of existing reference monitors.

A low-cost monitor for measurement of fine particulate matter and aerosol optical depth – Part 2: Citizen-science pilot campaign in northern Colorado

“…The continuous PM 2.5 sensor (Plantower PMS5003) estimates the PM 2.5 mass concentration based on the amount of 650 nm laser light scattered at a 90 • angle. The resolution of the Plantower PMS5003 is 1 µg m −3 , and it is stated by the manufacturers that it is effective for measuring concentrations in the range of 0-500 µg m −3 , with an accuracy of ±10-15 µg m −3 (Yong, 2016). Our use of the PMS5003 estimates the wet PM 2.5 mass in equilibrium with the ambient relative humidity.…”

“…The AMOD was mounted on a stationary camera tripod, and sampling and data collection were controlled by participants using the CEAMS app on a smartphone through a Bluetooth connection with the device, as described in Wendt et al (2019). After each sampling event, participants used the smartphone application to download data from the instrument to their phone and then send the data to our server using file transfer protocol (FTP).…”

“…This is not an exact compar- ison, as the CEAMS measurements have overlapping days and different sampling periods (different start and end times). However, our goal is not to validate our measurements (for validation, see Part 1 by Wendt et al, 2019) but to demonstrate that our measurements are able to capture a similar view of air quality to a traditional reference monitor. Concentrations were relatively low, and only a few filters measured concentrations above 12 µg m −3 .…”

“…However, there could still be some erroneous values due to a slight misalignment or the presence of thin clouds. After removing measurements that did not meet our criteria, we ended up with 115 AOD values for our analysis; as we used the same filtering criteria in Wendt et al (2019), we would assume the same quality as that quantified in those validation experiments.…”

“…The AMOD measures (1) time-averaged PM 2.5 concentrations (using a filter sample that can be analyzed for mass and composition), (2) AOD at four different wavelengths (using optically filtered photodiodes), and (3) continuous PM 2.5 concentrations (using an optically based sensor). While more expensive than some commercially available low-cost sensors, the AMOD is a fraction of the cost (∼ USD 1000 for the instrument and ∼ USD 30 per filter for materials and analysis; Wendt et al, 2019) of traditional surface-based instruments used for regulatory monitoring of air quality and can be deployed by trained citizens to measure AOD, PM 2.5 , and η.…”