About air monitoring

Notes:

1. PM2.5 represents fine inhalable particulate matter, with an aerodynamic diameter smaller than 2.5 microns. It is expressed in micrograms per cubic meter (µg/m³). Vehicle traffic is an important source of PM2.5 among multiple other sources. At this monitoring site, PM2.5 primarily helps us monitor particle pollution near-road. More details about this pollutant can be found on the EPA site.
2. The graph shows daily concentrations of PM2.5 relative to the 24-h average NAAQS. Daily values above this standard cannot be interpreted as exceedances as this is not a regulatory monitor and will not be included in design value calculations. When sufficient data is acquired to appropriately average, the PM2.5 concentration can be more directly compared with the annual NAAQS, which is based on 3-year average of annual data. Note that PM2.5 is not monitored for regulatory purposes at this site.
3. No data is represented as a gap on the plotted time-series. Data gaps are acceptable as they represent downtime due to instrument maintenance and/or routine quality assurance.

Notes:

1. Nitrogen Dioxide (NO2) and nitric oxide (NO) are the two primary gaseous pollutants classified as NOx, which play an important role in the formation of ground level ozone. NO2 concentration (in parts per billion, ppb) is generally higher than that of NO and other nitrogen oxides, the reason for which it is used as an indicator for a larger family of nitrogen oxides. From the NOx group, only NO2 is a regulatory pollutant and has corresponding NAAQS for both 1-h (100 ppb) and 1-year average (53 ppb), as shown with the orange line in the above graph. Main source of NOx is combustion, including emissions from vehicle traffic. More details can be found on the EPA site
2. When sufficient data is acquired, the hourly NO2 concentration can be appropriately averaged for direct comparison with the 1-year NAAQS (53 ppb). Note that NO2 is not monitored for regulatory purposes at this site.
3. No data shows as a gap on the plotted time-series. Data gaps are acceptable as they represent downtime due to instrument maintenance and/or routine quality assurance.

Notes:

1. Carbon monoxide (CO) is a gaseous pollutant that is primarily emitted from combustion, including from vehicle traffic emissions. If inhaled in excessive concentrations for long periods of time, CO can be harmful to human health. Concentration is expressed in parts per million (ppm). More details can be found on the EPA site.
2. CO is a regulatory pollutant and has two primary NAAQS, an 8-h average (9 ppm) and a 1-h average (35 ppm). In the graph, hourly concentrations are compared with the 1-h NAAQS.
3. No data shows as a gap on the plotted time-series. Data gaps are acceptable as they represent downtime due to instrument maintenance and/or routine quality assurance.

Notes:

1. Temperature and relative humidity are two important meteorological measurements that help understand the ambient conditions being monitored, ensure the instruments operate in their designed temperature range, troubleshoot instrument/sampling system errors, and inform data quality assurance. The two parameters are anticorrelated.
2. No data shows as a gap on the plotted time-series. Data gaps are acceptable as they represent downtime due to instrument maintenance and/or routine quality assurance.

Notes:

1. Wind measurements (direction and speed) are very important meteorological parameters that help understand potential sources of pollutants. Wind direction is measured in compass degrees: North (0 and 360 degrees), East (90 degrees), South (180 degrees) and West (270 degrees). Wind speed is measured in miles per hour (mph). Low wind speeds are indicative of stagnant air conditions, which favor accumulation of pollutants and chemical reactions.
2. No data shows as a gap on the plotted time-series. Data gaps are acceptable as they represent downtime due to instrument maintenance and/or routine quality assurance.

Notes:

*Please note that there is no formaldehyde and acetaldehyde data reported in January 2024 due to sampling system malfunctioning.

1. 
   Benzene, 1,3-butadiene, and naphthalene are three hazardous air pollutants (HAPs) or toxic air pollutants; they are also part of the volatile organic compounds group (VOCs). One of their sources is vehicle traffic emissions and therefore are relevant to the near-road monitoring. Their concentrations are expressed in ppb by volume (ppbv). Their concentrations are expressed in ppb by volume (ppbv). More details can be found on the EPA site.
2. In this monitoring program, these HAPs are measured over 24 hours, every 6 days, using canister samples. Canister samples are analyzed in the contracted laboratory with a turnaround up to 30 days (EPA Method TO-15A).
3. A single exceedance will not necessarily mean a health effect will occur but that more investigation is needed.
4. Their 24-h average concentrations are compared with health based AMCV (100 ppb for benzene, 430 ppb for 1,3-butadiene, and 41 ppb for formaldehyde). For longer averaging periods, data can be compared with the long-term AMCV (1.4 ppb for benzene, 9 ppb for 1,3-butadiene, 9.5 ppb for naphthalene, 8.9 ppb for formaldehyde, and 25 ppb for acetaldehyde). More information about TCEQ AMCVs can be found on the TCEQ site.

Notes:

*Please note that there is no formaldehyde and acetaldehyde data reported in January 2024 due to sampling system malfunctioning.

1. The 24-hour Air Monitoring Comparison Values (AMCV)

• 1,3 Butadiene = 430
• Benzene = 100
• Formaldehyde = 41

2. Because there are no 24-hour AMCV’s for Acetaldehyde and Naphthalene, short-term AMCV’s were used, and are as follows:

• Acetaldehyde = 250
• Naphthalene = 95