Ground Ozone Levels are Decreasing
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Ozone Exceedances
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(Number of exceedances
of one-hr. standard)
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Source: Rhode Island DEM, Office of
Air Resources
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The 1990s have witnessed a remarkable decrease in the number of one-hour ozone standard exceedances in Rhode Island. The national ambient air quality standard (NAAQS) for ozone is 0.12 parts per million averaged over a one-hour period. Hourly values of 0.125 parts per million and above are considered exceedances of the ambient ozone standard. The DEM Office of Air Resources measures data at four stations in Rhode Island. The graph above depicts trends at those stations over the course of the past decade; a decreasing trend is noted for all stations. It may seem counterintuitive that ozone exceedances have been more common at the West Greenwich station relative to the Providence station - isn't air quality generally at its worst in urban centers, with cleaner air as one moves away from cities? The confounder in this situation is that the nitrous oxides emitted by cars, more prevalent in urban areas, reacts with ozone in the atmosphere and artificially lowers ground ozone levels.
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Ozone Exceedances
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(Number of exceedances
of eight-hr. standard)
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Source: Rhode Island DEM, Office of
Air Resources
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In July 1997, the EPA revised the 1-hour primary standard and replaced it with an 8-hour standard at a level of 0.08 ppm. The 0.08 PPM, 8-hour primary standard is met at an ambient air quality monitoring site "when the 3-year average of the annual fourth-highest daily maximum 8-hour average ozone concentration is less than or equal to 0.08 PPM." The implementation of the new 8-hour standard was vigorously contested by industry, but in a recent US Supreme Court Ruling, the new standard was upheld, though its final implementation plan is still being written by the EPA.
Despite these trends, ground level ozone in New England continues to present a challenge to citizens and regulators alike. New England's air exceeded the 8-hour ozone standard on 30, 28 and 35 days in the years 1997, 1998, and 1999, respectively. New England's ozone levels are usually at their maximum between 1:00 and 7:00 PM during the spring and summer. The EPA-New England Air Quality Index page contains real-time and forecasted air pollution data for the region. (Source: US EPA)
Ground-level ozone is formed by a chemical reaction between VOCs and oxides of nitrogen (NOx) in the presence of sunlight. The number of exceedance days in Rhode Island have decreased over the past decade. Ozone concentrations can reach harmful levels when the weather is hot and sunny with calm winds - in fact, weather is generally considered to be the primary factor affecting ground-level ozone. The respiratory effects of ozone are felt in some individuals even at relatively low levels. Several groups of people are particularly sensitive to ozone - especially when they are active outdoors - because physical activity induces faster, deeper breathing. Most commonly affected are children, asthmatics, or others affected by respiratory diseases, and active adults. In general, as concentrations of ground-level ozone increase, there is an increase in ozone-related health effects, and the effects become more serious.(Source: US EPA)
Other Air Toxics Data:
National Air Quality Standards
For more information:
http://www.state.ri.us/dem/programs/benviron/air/ozone.htm
A site devoted to forecasting ozone levels across Rhode Island
and detailing associated health effects.
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