When walking outside on a muggy summer day, most people don’t look up at the sky and wonder about the air quality — it’s usually the last thing on people’s minds. However, criteria pollutants can negatively affect human health if levels get too high. The Environmental Protection Agency has created a color coded system, called the Air Quality Index, to alert the population when the air quality becomes dangerous. Viney Aneja, professor in air quality and environmental technology, helped Technician break down the meaning behind the science.
1. There are six criteria pollutants that are the most pervasive in the atmosphere – carbon monoxide, lead, particulate matter, nitrogen dioxide, ozone and sulfur dioxide. These pollutants have the biggest effect on air quality and our health.
“That is not to say that these are the only six that have an impact on us and our welfare, but they are the ones we believe are prevalent in the atmosphere all the time and will have an impact on us,” Aneja said. “We have done health affect-related studies. We have exposed cats and rats and dogs and mice to these pollutants and seen they – at a certain concentration – begin to have an adverse impact on [the animals], which are somewhat models of the human system. Then we can extrapolate from there that humans will experience an impact.”
2. For each pollutant there is a primary and secondary standard. The primary standard represents its impact on humans. The secondary standard represents its impact on human welfare – buildings, environment, vegetation – everything that isn’t human health.
“One hour concentration ought not to exceed 35 ppm (parts per million) for carbon monoxide. This 35 ppm is the National Ambient Air Quality Standard (NAAQS) for one hour of carbon monoxide, which means for one hour the concentration of CO should not exceed 35 ppm,” Aneja said. “Similarly, there is an eight hour standard. We make measurements of carbon monoxide continuously and we average this continuous measurement for one hour. That’s the starting point for air quality indexing.”
3. Criteria pollutants have different concentration values, but in order for the general public to understand the air quality index, the NAAQS is arbitrarily set at 100.
“For example, one hour of carbon monoxide at 35 ppm will have a value of 100 (units). Sulfur dioxide at 75 parts per billion would have a value of 100. We have brought all these six pollutants to a common denominator with the help of the air quality index and it is 100,” Aneja said. “A value of 100 units for the pollutant means that is the maximum tolerated by the NAAQS. Above 100 would be harmful to us; below 100, we’ll be OK.”
4. Value ranges correspond to different colors, ranging from green to maroon. Green and yellow, representing levels below 100 units, indicate the air quality is generally safe for everyone. Any higher than 100 units, indicated by code orange up to code maroon, begins to be unsafe for the public.
“In general, when the public sees green, everything is hunky-dory. When it says red, purple and maroon it sees things are going bad. In Raleigh and in the state of North Carolina in general, there are only two pollutants that we need to concern ourselves with – ozone and particulate matter. If any of the pollutants reach orange, then it is a code orange for the air quality as a whole. It doesn’t have to be all six [pollutants], it can be any one of them,” Aneja said. “During summer, we normally approach orange, but never exceed orange. Orange is above the NAAQS. Most of the time we are in moderate and good in Raleigh and the Triangle. We never go to red, purple or maroon. Los Angeles is purple – there are so many cars and its topography is a valley.”
The Air Up Here:
What pollutants affect Raleigh/the Triangle the most?
Particulate matter and ozone are the two pollutants that approach and sometimes exceed the national air quality standard in Raleigh and surrounding areas during the summer.
“Particulate matter and ozone are formed in the atmosphere, not emitted into the atmosphere. [The other 4] are emitted into the atmosphere, not formed. As the temperature increases during the summer, these pollutants react faster and produce more and more ozone and particulate matter,” Aneja said.
The Clean Air Act
“Our nation’s ability to manage our air is based on the Clean Air Act. The Clean Air Act was written in 1970, but it was amended in 1976 and it was amended again and it was last amended in 1990, which was under George Bush [Sr]. The Clean Air Act says we have the luxury to make changes to the act based on new science,” Aneja said.