Particulate air pollution is a big problem in the Sacramento area at the instant.
I queried the Purple Air website for raw PM2.5 levels, particulate air pollution smaller than 2.5 microns in diameter, in micrograms per cubic meter (ug/m^3), the size that most-affects lung function, averaged over one day.
The 24-hour national standard is 35 ug/m^3, so it's concerning we have levels around 50 ug/m^3 right now. You might be able to notice the bad air from your scratchy throat.
So, what gives? These particles are made mostly of ammonium nitrate. Particulate formation is often ammonia-limited in the summertime, but around here, under foggy wintertime conditions, that limitation is removed. The atmosphere goes hog-wild. There is plenty of ammonia and nitric acid and since one's a base and one's an acid they readily get together. Soon the air becomes filled with particles.
Here is AI's summary regarding particulate formation in the San Joaquin Valley (which is the same process that occurs elsewhere in California, including the Sacramento Valley):
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Key Findings on Wintertime PM2.5 and Ammonia Nitrate-Driven Pollution:
High winter PM2.5 concentrations (often exceeding 35 (ug/m^3) are largely driven by the combination of NOx (from traffic/industry) and NH3 (primarily from agricultural sources) to form ammonium nitrate.
Limiting Factors: While the San Joaquin Valley has an excess of ammonia, NOx reductions are more effective than NH3 reductions in lowering wintertime ammonium nitrate levels.
Seasonal Peaks: PM2.5 concentrations in the Valley peak during winter due to stagnant air, fog, cold temperatures, and increased wood burning, with ammonium nitrate concentrations being three times higher in December than in June.
Regional Differences: In the SJV, ammonia is typically in excess, whereas in the South Coast Air Basin (LA region), wintertime PM2.5 may show different, more ammonia-limited characteristics due to regional differences in emissions.
Factors Influencing Winter PM2.5 Levels
Meteorology: Inversions, cold temperatures, and lack of rain trap pollutants, creating elevated, multi-day episodes.
Emission Sources: Key sources include residential wood burning (organic carbon) and ammonium nitrate formed from NOx and agricultural ammonia. Contribution of Ammonia:
Despite being often NOx-limited, ammonia is still crucial to the inorganic PM2.5 mass; studies show that over 50% of inorganic PM2.5 in California is linked to anthropogenic ammonia.
