In the United States, the region with the worst fine particulate matter pollution problem is – you guessed it – California’s San Joaquin Valley. Fine particles, though actually less than 2.5 micrometers in diameter in size, are nevertheless given the designation PM 2.5. These particles are roughly one-thirtieth the width of an average human hair.
In an article in The Fresno Bee, meanwhile, referenced is a San Joaquin Valley Air Pollution Control District (air district) daily PM 2.5 health standard of 20 micrograms per cubic meter of air. It is important to note this was tightened from the air district’s previous 24-hour fine particulate matter standard of 30. Also noted in the same Bee article is another number: 470, in this case referring to the number of wood-burning violations recorded for the winter 2014-’15 season when rules on wood-burning are in effect. This is a slight improvement over the prior winter’s 547 violations. Wood-burning rules are in effect in the Valley Nov. 1 through Feb. 28.
Meanwhile, from the California Environmental Protection Agency Air Resources Board’s “Air Quality and Meteorological Information (AQMIS2)” page, 49 is the number of days the Valley exceeded the 24-hour federal PM 2.5 health standard of 35 micrograms per cubic meter of air this winter (30 in Jan. and Feb. 2015 and 19 in Nov. and Dec. 2014), this compared with the South Coast Air Basin’s 25 (20 in Jan. and Feb. 2015 and 5 in Nov. and Dec. 2014). The number of times the Valley exceeded the federal PM 2.5 standard last year (Nov. 1, 2013 through Feb. 28, 2014) was 71.
Add to this that during winter 2014-’15 up to this point in time, that is, more rain fell compared to last winter and there has been more Valley fog. Rain totals are recorded from Jul. 1 to Jun. 30. This may have contributed to the fewer number of exceedences this year compared to last.
There are other factors that could have come into play as well.
“Through February, nearly 3,000 wood-burning devices were registered with the District as meeting current [U.S. Environmental Protection Agency] emission standards,” the air district in a Feb. 26, 2015 news release emphasized.
“This winter, as of Feb. 26, there were 36 days when wood-burning was not allowed for anyone in at least one county. Comparatively, last winter, there were a total of 376 curtailments throughout the air basin.”
The Valley county with the most curtailments or prohibitions in 2013-’14 was Fresno, with 59. The county with the fewest was Merced with 25, according to the air district in the release.
What was different also wood-burning-wise this season compared to last, for EPA-approved and air-district-registered wood-burning devices, as long as daily PM 2.5 levels were expected to be 65 micrograms per cubic meter or less, their use was allowed. Last year, if the threshold of 30 micrograms per cubic meter of air was expected to be exceeded, there was no wood-burning, with one exception, that being, if residents had no other way to heat their homes.
In no uncertain terms, the air district has made quite clear that, “[t]his season, there were fewer days during which the fine-particle level exceeded the federal health standard of 35 micrograms per cubic meter. There was also more rain and less atmospheric stagnancy than last winter, although the statewide drought continues with associated air-quality effects.”
The air district, meanwhile, is discouraging residential wood-burning even though formal wood-burning restrictions aren’t in force any longer in the Valley effective as of Mar. 1st.
Look for temperatures later this week to return to the 70s. Expect with that levels of air-pollutant emissions to rise too.