March 24 – San Diego Reader – Sheila Pell Reports – Almost a week after the county banned large gatherings and life-as-usual came to a halt, the air has changed. From Otay Mesa to Oceanside, the color-coded maps that show where air pollutants concentrate are green, the lowest risk.
The air is good in Alpine where smog, corralled by mountains, settles, and in San Ysidro, a hotspot for border-fumes. Since the majority of air pollution in San Diego is caused by vehicle emissions, the coronavirus shutdown has led to clearer skies, as it has in China, Italy, New York City and beyond.
“We can be certain that there have been fewer emissions with reduced traffic over the past week,” says Bill Brick, chief of air monitoring and technical services at San Diego Air Pollution Control District. “Our air monitoring data do show relatively low concentrations of pollutants. Ozone is near background levels due to a well-mixed atmosphere.”
Other pollutants, however, like PM2.5 and nitrogen oxide, may be lower due to recent storms washing them away. “So it’s difficult to quantify as long as the atmosphere continues to be unstable.”
But in January, the system at full throttle, air maps showed fiery hues in some areas, indicating unhealthy air. The county earned failing marks from the American Lung Association last year for having the sixth-highest rate of ozone pollution in the country from 2015 to 2017.
The county is currently in non-attainment of state and federal designations for eight-hour measurements of ozone, and state designations for one-hour measurements of ozone, as well as particles PM 10 and PM 2.5, which can worsen asthma. (California adopted its own stricter standards in the Clean Air Act of 1988).
Wildfires and pollutants that blow in from other cities don’t help, but at least for now, they don’t hurt, either. The South Coast Air Basin (Los Angeles area) has reported lower concentrations of air pollutants since the slowdown.
Brick says the South Coast Air Basin typically brings some additional ozone to San Diego at this time of year, though far less than it did decades ago. Heat, however, hasn’t subsided. Ozone levels vary by year, and warmer conditions contribute to higher numbers, as seen in 2016 and 2017.
“These ozone values go into the calculation of our design value,” he says, which is a three-year running average of the fourth highest eight-hour ozone value – at Alpine. It’s used to determine compliance with federal air standards.
The biggest contributor in the county, however, are vehicles, he says. Over the long-term, air pollution is improving due to cleaner vehicles and other emissions reductions. It’s too early to calculate the results of the current pause.
“Air pollution levels are strongly linked to the meteorology, so timing and intensity of returning to the normal economy and emissions is hard to pin down.”