July ’15 sees better air quality in Valley – is Mother Nature or are humans responsible?

July 2015 in California’s San Joaquin Valley, as far as July’s go, was one of the least smoggy. Though the air quality data is still preliminary, there were no exceedances of the federal eight-hour health standard for ozone on 21 out of July’s 31 days.

So, what’s behind the improvement? Favorable weather conditions such as overcast (cloudy) skies, wind and even rain, all three, perhaps, or, is it something else like tougher air quality rules imposed by the San Joaquin Valley Air Pollution Control District?

Before getting too, too excited, several key pieces of information.

First, for year 2015 the National Ambient Air Quality Standard that applies regarding ozone is 75 parts per billion (ppb). This was established by the U.S. Environmental Protection Agency (EPA) on Mar. 27, 2008 and it applies to both primary and secondary ozone, averaged over eight hours. So, a reading of 76 ppb or over constitutes an exceedance and corresponds to an Air Quality Index (AQI) reading of 101 or higher.

Next, in looking at data from July 2015, there were a total of 10 ozone exceedance days. The days on which there were no exceedances recorded, incidentally, does not necessarily mean good air quality on those days. For instance, on Jul. 21st, the data reveals that the recorded ozone level was 71 parts per billion (0.071 parts per million). Ozone levels of between 60 ppb (0.06 ppm) and 75 ppb (0.075 ppm) correspond to AQI readings of between 51 and 100, putting air quality in the moderate range.

Now, it is important to consider what Valley meteorological conditions were on each of July’s 31 days. In trying to draw conclusions, weather being an important factor, questions to ask are:

  • On the days with ozone exceedances what meteorological conditions were present throughout the Valley at the time?
  • On the days without ozone exceedances what meteorological conditions were present throughout the Valley?
  • Were there any days where factors other than weather may have played a contributory role in helping to prevent an exceedance from occurring?

This requires further explanation. Say, for example, high temperatures were present, but perhaps motor vehicle activity was subdued as might happen on a Sunday or holiday. As it were, July 4th this year fell on a Saturday. Temperatures by late afternoon in many Valley locations hovered near the century mark. Also during the 4th of July holiday, outdoor grilling activity is typically more pronounced. What, if any, effect did this have? All of this information could help in determining the reason(s) for the general improvement in air quality this July, that is, compared to all July’s, 2008 to 2014, the years with the more stringent 75 ppb ozone standards in effect.

In much of the region throughout much of July, unstable air was present. One source indicated that there was above average precipitation with some areas receiving record rainfall amounts for July and that on most days the weather was unseasonably cool as a marine layer made its way into the Valley and remained until high pressure pushed the marine layer out. It was mainly during these high-pressure, higher-temperature periods that ozone pollution began building and national ambient air quality standards averaged over eight hours were exceeded. Many of these exceedances (eight, actually) occurred during the first few days of the month as well as the last several days of July when temperatures in many locations reached 100 degrees or higher. A high of 108 degrees occurred in Fresno on Jul. 29th. Bakersfield’s high that day was 107 degrees according to this same source. A ridge of high pressure with accompanying high temperatures was present as well for two days in a row beginning on Jul. 16th. Ozone standard exceedances in the Valley also occurred on these days. In all, there were 10 exceedances for the month. This compares with July 2014’s 28 exceedances. In addition, subtropical moisture made its way into the Valley and in the higher elevations of the Sierra Nevada Mountains on more than one occasion. Tropical moisture associated with Hurricane Delores was dumped on the Valley floor on the 18th in the form of showers and thunderstorms and lingered for several days; some areas hit by flash flooding on account of these. July 2015 in the Valley and California, for the most part, was a wet, wild and windy month.

Meanwhile, July ’15’s mean ozone value was 70 ppb (0.070 ppm). Incidentally, the lowest air quality reading in the Valley was for Jul. 9th which measured 48 ppb (0.048 ppm) indicating good air quality. This compares with July ’14’s mean ozone value of 82 ppb (0.082 ppm). Remember, this reflects the average of daily eight-hour (highest) readings, from July 1st through July 31st.

So, in a related The Fresno Bee article, cited was San Joaquin Valley Air Pollution Control District Executive Director Seyed Sadredin, who seemed to have pointed to tough new ozone regulations, seemingly more so than cooperating meteorological conditions that made the difference this July compared to others. Although no specific rules were mentioned, it was, however, explained that, if I understand what was emphasized in the article in question correctly, it is as a result of rules requiring businesses and industrial and other sources to scale back their releases, particularly oxides of nitrogen (NOx) and volatile organic compounds (VOC) – such as those fumes released from gasoline, paints, solvents and dairy wastes, primarily – that is resulting in Valley air during the summer ozone season gradually getting cleaner. This is the way I interpreted what I read, at least. It remains to be seen how or if air quality for the remainder of the summer and also throughout the early part of autumn is going to be affected.

As it also has to do with ozone, there is one other point to bear in mind: The ozone that is in the stratospheric layer is naturally occurring ozone. This is the ozone layer that helps block the sun’s harmful ultraviolet light radiation from reaching the earth’s surface. Through physical processes some of the stratospheric ozone settles (drops) into the troposphere. This additional ozone into the troposphere adds to the ground-level ozone problem. Even though it in general is at relatively low levels, there is the presence of tropospheric ozone all year round; this in light of the fact ozone (its creation) is a warm-weather phenomenon.

Furthermore, it takes sunlight, heat and the mixing of chemicals in the air such as VOC and NOx to facilitate ozone’s formation. Cloudy skies, blowing breezes and/or rain are the most common conditions which help retard or even prevent ozone’s formation. Add in cool temperatures and the ozone retarding and prevention picture is complete.

Primary ozone is ozone created directly from combustion processes. Secondary ozone is that which is created indirectly, such as when fumes from gasoline (a volatile organic compound or VOC) combines with naturally occurring oxides of nitrogen (NOx) present in the air. The Bee article author mentioned the way in which lungs are damaged from the ozone scourge. There was one reference pointing out the ground-level ozone, when taken into the lungs, induces a chemical burn tantamount, apparently, to a sunburn on lung tissue, although, to be quite frank, I’m not sure I understand that latter explanation.

Quite interestingly, Tuesday’s high temperature in the Fresno region was 83 degrees and while Wednesday’s high temperature was 86, still, good air quality was forecasted throughout much of the eight-county Valley. We’ll take it!


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