2021 Air Quality Status

Ground-level ozone forms when nitrogen oxides (such as those found in vehicle exhaust) combine with volatile organic compounds (such as those found in gasoline fumes) during periods of intense sunlight. Ozone is the most prevalent form of air pollution in the Alamo region. Attainment of the Environmental Protection Agency's (EPA's) 2015 National Ambient Air Quality Standard (NAAQS) for ground-level ozone is based on a three-year average of the annual fourth highest, eight-hour reading at any one of the area’s three regulatory monitors, which are located at Calaveras Lake, Camp Bullis, and Marshall High School (referred to as San Antonio NW). In order to be in compliance with the standard, the three year average must be no higher than 70 parts per billion (ppb) at all three regulatory monitors.

Table 1 below lists the four highest daily maximum eight-hour ozone concentrations measured at the area's three regulatory monitoring sites during the 2020 Ozone Season (which began March 1 and will end on November 30, 2021):

Table 1:  Four highest ozone readings of 2021 at regulatory monitoring sites (as of 06/16/2021)
 Monitoring Site  Highest  ppb  2nd Highest  ppb  3rd Highest  ppb 4th Highest   ppb
 San Antonio NW C23 04/11/2021 72 05/06/2021 67 03/26/2021
67 06/16/2021
 Camp Bullis C58 04/11/2021
76 05/07/2021
71 05/20/2021 70 04/25/2021 70
 Calaveras Lake C59 04/11/2021
67 03/26/2021
64 05/07/2021 62 04/25/2021 60

Table 1 shows that the fourth highest, eight-hour average reading at the three regulatory monitors in the region, San Antonio NW, Camp Bullis, and Calaveras Lake, were 66 ppb, 70 ppb, and 60 ppb, respectively, as of June 16, 2021.  When those fourth highest readings are averaged with the fourth highest readings from 2019 and 2020, and demonstrated in Table 2, below, the three year averages are 70 ppb at San Antonio Northwest, 71 ppb at Camp Bullis, and 63 at Calaveras Lake:

Table 2: 2019-2021 3-year average of 4th highest, 8-hour reading at regulatory monitoring sites
(as of 06/16/2021)
Monitoring Site 2019  2020
3-Year Average
San Antonio NW C23 75 69 66 70
Camp Bullis C58 69 74 70 71
Calaveras Lake C59 63 66 60 63
Source: https://www.tceq.texas.gov/cgi-bin/compliance/monops/8hr_attainment.pl

Although the 2021 readings have yet to be validated by the EPA, it appears that our three-year average is exceeding the standard for ground level ozone at one of the region's regulatory monitors: Camp Bullis C58. 

Bexar County has been designated nonattainment of the federal ozone standard since September 24, 2018, with the other twelve counties that surround San Antonio and make up the Alamo Area were officially determined to be "attainment/unclassifiable" earlier that year. Of six possible non-attainment categories that have progressively stricter regulations designed to reduce pollution and bring them back into compliance with the federal standards, Bexar County was placed in the least strict (marginal) category, due to the fact that its violations register just slightly over the threshold. This triggered a three-year clock to bring ozone levels into compliance, or else risk being reclassified to the moderate category.

The nonattainment designation's requirements, even at a marginal level, directly impact new or expanding businesses as well as transportation agencies, and will have rippling effects throughout the region's economy.  It is expected, however, that these requirements will help bring healthier air to the area.  At the moderate nonattainment level, more stringent requirements, such as mandatory vehicle emissions testing, will be implemented in Bexar County.