I’m sure almost no one saw this coming: One of the wettest January’s in the San Joaquin Valley on record. In Fresno County alone, nearly 4 inches of rainfall fell. That’s more than a third of the county’s average annual rainfall total of 10.99 inches. All told, the 2022-‘23 season – which runs from Oct. 1 through Sept. 30 – so far, the skies have opened up and dumped 9.20 inches of rain in this central California community. At least one Central Valley county with rain totals on the Valley floor that surpasses Fresno’s is Merced, which has recorded over 12 inches thus far.
This after years if not as many as two-plus decades of drought conditions.
Quite astonishingly, for the entire month of Jan. this year, Fresno County did not record a single day of unhealthy air for sensitive individuals or worse for the pollutant fine-particulate matter or PM2.5 regarding the 24-hour average – also known as the “average daily” reading.
In this thread, we zoom in closer on precipitation numbers and PM2.5 readings in Fresno County during the month of January 2023.
Precipitation events
California’s San Joaquin Valley got an abundance of rain last month; and that’s putting it mildly. Locations in both the north and central Valley regions were so hard hit that localized flooding occurred, both in and around the Merced area and in the small farming community of Planada, located just south of there. And there was at least one funnel-cloud sighting. If you want to know when the last time the region has seen this much rain in so short a period of time, you have to go back to the 1990’s or earlier, as far back as the first half of March 1989, when for 10 days straight, precipitation moved in off the Pacific Ocean and dumped it as rain on the Valley floor and in the Sierra foothills and as snow in the Sierra Nevada Mountains themselves, that is, at elevations above 5,000 feet.
In Fresno County, between the 1st and the 19th of Jan. ‘23, rain fell every day except on 1/3, 1/6, 1/12, 1/15 and 1/18 – five days. As for the rest of the month (between Jan. 20th and the end of the month), there were no other days that had rain.
Fresno air quality
Air quality for Jan. this year for daily average PM2.5 at the highest site ranged in concentration from a low of 2.5 micrograms per cubic meter on 1/9 to a high of 34.6 micrograms on 1/29. (Source of the PM2.5 data used right here and previously in the post: the California Environmental Protection Agency Air Resources Board).
These numbers alone, do not tell all there is to know. According to the U.S. Environmental Protection Agency document titled: The National Ambient Air Quality Standards for Particle Pollution,” in the section identified as “Revisions to the Air Quality Index,” and as shown in the table on page 4, daily average PM2.5 is considered to be in the Good range (AQI between 0 and 50) if the level is 12.0 micrograms per cubic meter or lower. If daily average PM2.5 falls between 12.1 and 35.4 micrograms per cubic meter, the corresponding AQI lands between 51 and 100 and the corresponding air quality is deemed to be in the Moderate range. For Jan. ‘23, for Fresno County, where average 24-hour PM2.5 is concerned, there were 18 days in all of good air quality. On 13 days on the other hand, in Fresno County, for fine-particle pollution, air quality was moderate.
Interestingly, with 12 days in all last month in the county where air quality was moderate there was also no precip. However, there were also days without rain where the air quality happened to be good: 1/3, 1/15, 1/18 and 1/30. Meanwhile, most days with good-quality air (11 in all), had measurable rainfall. (Sources of data used right here, the California Environmental Protection Agency Air Resources Board and the National Weather Service). It’s entirely possible, rain could have been a contributing factor in the county air quality being good on those 11 days that rain did fall.
Calling soot what it really is: trouble
Soot or fine-particulate pollution is pollution at the microscopic level. Those specks are too small to see with the naked eye, less so the ultra-fine particulate matter.
When inhaled, such PM can become lodged deep in the lung or enter the bloodstream and travel to other organs as well as to the brain which, while there, can impede cognitive function.
Bottom line: No matter the air concentration of fine or ultra-fine PM, a speck of soot breathed in and finding its way to the lung, or the cardiovascular or circulatory systems, the potential exists for harm to health to be caused – irreparable health harm or otherwise.
Corresponding, connected home-page-entry image: U.S. National Institutes of Health: National Heart, Lung and Blood Institute
– Alan Kandel
Copyrighted material.
Last edited on Mar. 2, 2023 at 5:17 a.m. Pacific Standard Time.