Emory Air Quality (Emory AQ) is an effort to monitor and report air pollutant concentrations at and around Emory University’s Main Campus. The high levels of industry and traffic in and around Emory University raised the question “is it safe to breathe this air?” Emory AQ started first with a focus on measuring particulate matter (PM) concentrations, temperature, and relative humidity at Emory University campus. That has then expanded to the initiative in Atlanta schools and now we have expanded to the Metro Atlanta Clean Air Initiative (MACAI).
What is PM?
Particulate Matter (PM) consists of small particles and liquid droplets suspended in the air. Their chemical properties are determined by the composition of these solid and liquid particles. We measure PM using a Dylos sensor, which divides PM into two categories: 2.5 to 10 micrometers in diameter (PM10), and 2.5 micrometers or smaller (PM2.5). The national standard for PM2.5 is 9 µg/m^3 and for PM10 is 35 µg/m^3.
Why Relative Humidity?
The Dylos particle counter doesn't take into account relative humidity when measuring the PM. This is a problem because if humidity is high, water will attach to particles and cause the particles to become larger. Thus the Dylos measures the particle as bigger than it actually is.
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A good write-up of how humidity affects PM can be found here, a paper on research done in China can be found here, and information from the EPA on PM2.5 formation and relative humidity can be found here.
Assumptions
In order to translate from PM to volume of particulates, we assumed that all particles are spherical and used an average density to calculate the volume of PM (μg/m^3). Both temperature and humidity affect the sensors that measure PM, which may skew the data in some conditions.
This is a project by the Saikawa lab at Emory University.
This project is funded by the Emory Department of Environmental Science and the Office of Sustainability Initiatives (OSI).
This project was inspired by Berkeley BEACON.