Emory Air Quality (Emory AQ) is an effort to monitor and report air quality around Emory University’s Main Campus. The high levels of development and traffic in and around Emory University raised the question “how clean is the air we breathe?” For this reason, Emory AQ currently monitors particulate matter(PM), temperature, and relative humidity.
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 in diameter(PM2.5). The national standard for PM2.5 is 12 micrograms per meter cubed and for PM10 is 35 micrograms per meter cubed.
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.
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.
Environmental and Health Concerns
PM, when inhaled, possesses a risk of aggravating or causing cardiorespiratory problems: asthma, lung and heart disease, difficulty breathing, and irritation. The smaller the particle, the deeper it can penetrate your lungs, or even your blood stream. For this reason, PM2.5 poses a greater health risk than PM10, pollen, or other large dust particles. Environmentally, the chemical composition of PM can contribute to chemical weathering, crop damage, and alter the pH of aquatic ecosystems. The EPA provides more information here.
How Do We Report Air Quality?
The Environmental Protection Agency (EPA) establishes a National Ambient Air Quality Standard (NAAQS) for five major air pollutants (ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide), regulated by the Clean Air Act. These standards are used to establish the U.S Air Quality Index (AQI), a reporting index that categorizes the air into six degrees of health concern. For , the AQI criteria for “Good”, satisfactory air with little or no risk, is 12.0 micrograms per meter cubed. Anything beyond this threshold introduces risk to sensitive groups, such as those with asthma, as air quality decreases further.
More About AQI
Good: The air poses no risk.
Moderate: For most people, the air poses no risk. The air may be hazardous for a very small number of people sensitive to specific irritants.
Unhealthy for Sensitive Groups: For most people, the air poses no risk. The air is hazardhous for young children, older adults, and those with heart and/or lung conditions.
Unhealthy: Most people will start experiencing negative effects from the air. Sensitive groups will have more severe symptoms.
Very Unhealthy: Everyone will experience more serious symptoms.
Hazardous: Entire population will be extremely negatively affected.
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/m3). Both temperature and humidity affect the sensors that measure PM, which may skew the data in extreme conditions.