Air Quality Index Case Study

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Measuring Air Quality
Air quality is measured using the Air Quality Index (AQI). Developed by the Environmental Protection Agency (EPA), the index monitors five major air pollutants and measures the level of health concern these pollutants cause. The index was mandated under the Clean Air Act in 1976, it was originally called the Pollutant Standards Index. The AQI is used internationally. In the United States, all cities with populations larger than three hundred and fifty thousand are required to report AQI results each day. (AirNow, n.d.; EPA, n.d.).
The AQI measures fine particulate matter pollution and Ozone (O3), two pollutants of concern in the U.S. The AQI also measures, Carbon monoxide (CO), Nitrogen Dioxide (NO2), and Sulfur Dioxide (SO2). Using a scale of 0-500, results fall into six categories: Good (≤ 50), Moderate (51-100), Unhealthy for sensitive groups (101-150), Unhealthy for everyone (151-200), Very Unhealthy (201-300), and Hazardous (> 300).
San Francisco’s AQI
On Tuesday, July 28, 2015, the Bay Area Air Quality Management District (BAAQMD) reported on their website (, for San Francisco:
Table 1.
Particulate matter Based on 24-hour concentrations (using PM2.5) 57 Moderate
Ozone Based on 8-hour average concentrations 41 Good
Carbon monoxide Based on 8-hour average concentrations 12 Good
Nitrogen Dioxide Based
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Located about fifteen miles from the City of San Francisco is the Chevron Richmond Refinery, a 2900 acre facility that processes a quarter of a million barrels of crude oil every day (Chevron, n.d.). The SF Bay Area is also home to the Port of Oakland, ranked in 2013 as the fifth busiest container port in the United States. California’s freight system, which includes maritime shipping, is the “…single largest contributor of diesel particulate matter (soot) and smog-forming nitrogen-oxide emissions in the state” (UCS, 2014, p.

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