People who visit Los Angeles or Denver during the time when both cities experience the atmosphere’s inversion layer understand the definition of smog. The concentration of the smog is so thick that one cannot detect the urban landscape while perched on top of a mountain ridge. Once you travel down the mountain side towards the city, your eyes burn from the toxic chemicals suspended in the air around you.
On days such as those, the air quality index is at the highest point of the unhealthy category. We rarely see such dangerous air quality levels in the Midwest, but we do experience a number of days during the summer when people with respiratory ailments need to take precaution. Air quality levels such as the ones measured in Los Angeles and Denver are categorized on the Air Quality Index (AQI). The AQI consists of the air quality categories, which the federal government uses to characterize the quality of the air at locations throughout the United States.
An increase in the AQI means an increase in the percentage of people adversely affected by the air quality. The instrument used to assess the ambient air quality and pollution is called the High Volume Sampler (HVS), from which concentration levels are recorded and compared to monitors or models. The AQI values are divided into ranges, and each range is assigned a descriptor and a color code. The EPA issues standardized public health advisories that are associated with each AQI range. The EPA may also encourage people to take public transportation or work from home during periods of high AQI levels.
The EPA measures three major pollutants: particulates, ozone, and carbon monoxide. Scientists find ozone in the ground level and upper layers of the atmosphere. Both ozone origins have similar chemical compositions, but only one of the origins is beneficial to a person’s health. Upper atmospheric ozone forms a protective layer from the sun's harmful rays, while ground-level ozone is the primary component of smog. Motor vehicles are the main culprits to the disbursement of ground level ozone, and urban areas with high traffic congestion such as Los Angeles become ozone incubators during certain times of the year. Scientists link ozone to respiratory irritation, chronic bronchitis, and diminished lung capacity. The elderly and small children are particularly vulnerable to high ozone levels.
Carbon monoxide is another poisonous gas emitted by motor vehicles. When it enters the bloodstream, carbon monoxide impedes oxygen from being delivered to the body's vital organs. People who suffer from cardiovascular disease are susceptible to developing additional complications from carbon monoxide exposure, particularly those with angina or peripheral vascular disease. The third type of air pollutant are particulates, which can be coarse (larger than 2.5 micrometers) or fine (less than 2.5 micrometers). Particulates come from windblown dust, grinding operations, fuel combustion, power plants, and wild fires. Scientific studies link fine particulates to such health concerns as aggravated asthma, chronic bronchitis, and diminished lung capacity. People who suffer through seasonal or condition specific allergies can have their symptoms exacerbated by the presence of particulate matter. Moreover, particulates also contribute to eye irritation.
While the EPA is responsible for measuring and monitoring air quality, local meteorologists disseminate the information as part of their forecasts during the times of year when the potential for air quality to decrease is high. The local National Weather Service (NWS) office begins their air quality forecasts around the middle of May, and runs them every day until the summer weather pattern breaks in early September. The EPA monitors heavily traveled roads with HVS devices during summer, and analyzes the results from the recorded data. The key to measuring air quality is concentration, and high concentration of three pollutants can become serious community health issues.