Silent component of smog fouls nighttime air quality

Introduction to Smog and Air Quality

A hidden pollutant that contaminates Southern California’s nighttime air is much more prevalent than previously thought, suggesting that air quality alerts underestimate the health effects of breathing smoggy air, a study released Wednesday reported. Researchers at Caltech and other academic institutions found that levels of ammonium nitrate made up half of the fine particulate pollution (PM2.5) on the region’s worst air days but are unaccounted for by air pollution control agencies.

The Impact of Ammonium Nitrate

This means air quality indexes of “good,” “moderate,” “unhealthy,” or “hazardous” released to the public may be worse than indicated. “When PM2.5 is measured and ammonium nitrate levels are high, the PM2.5 is underestimated because most of it evaporates before it is measured,” wrote the lead author of the study published in “Science Advances” on May 21, Ryan Ward. He did the work while a graduate student at Caltech in Pasadena and is now a post-doctoral fellow at Columbia University in New York.

Sources of PM2.5

PM2.5 are tiny pollution aerosols that originate from tailpipes of cars, trucks, ships in port and also fossil-fuel powered garden equipment. These particles can lodge deep into the lungs and the brain and are linked to poor health outcomes. Scientists and medical doctors have known for at least 20 years that breathing smog peppered with high PM2.5 levels is linked to cardiovascular issues, respiratory problems, and premature death.

Health Effects of PM2.5

Chronic exposure to PM2.5, the size of 2.5 micro meters or less, and the slightly larger variety, PM10 that’s 10 micro meters leads to hospitalizations, higher incidents of asthma and COPD and even death, according to a recent article by Dr. Olawale Amubieya, pulmonologist and junior faculty in the Division of Pulmonary and Critical Care Medicine at UCLA Health. Ward wrote that it’s not known if this inorganic chemical is more toxic than the other compounds found within PM2.5, he said, adding that in total, microscopic particulate pollution is a public health hazard.

Measuring Air Quality

Measurements of the Air Quality Index (AQI) don’t say what the smog is made of. With the new data, Caltech scientists and clean-air advocates suggest air quality regulators re-focus their attention on reducing ammonium nitrate, an often ignored element of smog. “This study should urge the U.S. EPA and California Air Resources Board (CARB) to address ammonium nitrate,” said Bill Magavern, policy director for the nonprofit Coalition For Clean Air in Los Angeles.

Reducing Ammonium Nitrate

Ammonium nitrate was measured using the Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT), a collection of scientific instruments that measure continuous air quality. ASCENT is funded by the National Science Foundation (NSF). Scientists could differentiate the compounds within PM2.5 by using the portal of ASCENT in Pico Rivera, combined with a mass spectrometer, Ward said. The spectrometer was first tested on the roof of Caltech Hall, the tallest building on the Pasadena campus, from January to June 2023.

Formation of Ammonium Nitrate

Ammonium nitrate is formed after oxides of nitrogen (NOx) molecules change into nitric acid, which combines with ammonia, creating ammonium nitrate. Ironically, smog-reducing regulations and less-polluting internal combustion engine automobiles burning gasoline or diesel fuels have reduced NOx and particulate levels in the South Coast Air Basin. However, this has produced a counter-effect, resulting in ozone, the primary smog component formed when chemicals react in sunlight, leaving the daytime air but hanging around in the nighttime air.

Reducing Fossil Fuel Emissions

California has a mandate that the state must sell no more gasoline-powered passenger vehicles. Starting in 2035, only battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) can be purchased. “The good news is California is trying to move cars, trucks, buses, lawnmowers to zero emission. The bad news is the Trump administration and Congress is trying to block all that progress and force us to burn more fossil fuels and breathe all that poison,” said Magavern.

Conclusion

In conclusion, the study by Caltech researchers highlights the importance of addressing ammonium nitrate, a hidden pollutant that contaminates Southern California’s nighttime air. The findings suggest that air quality alerts may underestimate the health effects of breathing smoggy air, and that reducing fossil fuel emissions is crucial to improving air quality.

FAQs

1. What is ammonium nitrate and how is it formed?
   Ammonium nitrate is a pollutant that forms when oxides of nitrogen (NOx) molecules change into nitric acid, which combines with ammonia.
2. What are the health effects of PM2.5?
   PM2.5 can lodge deep into the lungs and the brain and are linked to poor health outcomes, including cardiovascular issues, respiratory problems, and premature death.
3. How can ammonium nitrate be reduced?
   Reducing fossil fuel emissions by transitioning to zero-emission vehicles and appliances can help reduce ammonium nitrate levels.
4. What is the Air Quality Index (AQI) and what does it measure?
   The AQI measures the level of air pollution, but it does not indicate the composition of the smog.
5. What is the Atmospheric Science and Chemistry mEasurement NeTwork (ASCENT)?
   ASCENT is a collection of scientific instruments that measure continuous air quality, funded by the National Science Foundation (NSF).