About air monitoring
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About air monitoring

TxDOT is placing one air monitor in each I-45 North Houston Highway Improvement Project (NHHIP) segment one year in advance of the start of construction on the corresponding project segment. The first air monitor has been put in place in Segment 3 and this webpage will be updated to post the readings from this and subsequent NHHIP segment air monitors.

The air quality data available through this website have been provided by the contractor responsible for operating and maintaining the air monitoring station where the measurements are made. Each contractor is responsible for reviewing and assuring data quality prior to submitting it for use by this website and the public.

No data are posted to this website before they are quality assured. The time required for quality assuring the data varies and affects when data are ready for posting. It depends on the number of chemical compound measurements being checked and the calibration steps that must be reviewed for each measurement.

Most recent measurements at the TXDOT Near Road Air Quality Monitoring Site (NR-AQM-01)

Section 1: Data sources and data availability on the website

Ambient air measurements taken at the NR-AQM-01 site are provided by the contractor (AECOM) and they are quality assured. The contractor operates and maintains the site, validates the data, reviews and quality checks the data, and reports the data to TxDOT on a monthly basis. TxDOT updates the graphs on this website and makes the data available to the public at a similar frequency.

Continuous measurements reported on this website are criteria pollutants and precursors (PM2.5, NO, NO2, NOx, CO), and meteorology (relative humidity, temperature, wind direction and wind speed). Toxic air pollutants measurements are based on 24-hr canister samples (benzene, 1,3-butadiene and naphthalene) and 24-hr sorbent cartridge samples (formaldehyde and acetaldehyde) taken every 6 days by following closely the EPA sampling calendar. All pollutants presented on this website are compared to their respective National Ambient Air Quality Standards (NAAQS) or Air Monitoring Comparison Values (AMCV).

Disclaimer: The NR-AQM-01 is not a regulatory monitor that TCEQ/EPA uses for regional reporting and design value calculation purposes. Therefore, although criteria pollutants (i.e., PM2.5, NO2 and CO) may be approaching or exceeding the NAAQS at this site, they should not be construed as an immediate health concern or as actual exceedance of the NAAQS since they would not be incorporated into the official design value calculations used by EPA for designation purposes. Nor do they represent all locations of expected maximum representative concentrations in the area (Code of Federal Regulations. Title 40, Chapter I, Subchapter C, Part 58).

For official information and alerts on daily air quality conditions, please visit the EPA Air Now Website, the TCEQ Air Quality Index (AQI) website , or TCEQ Air Quality Forecast and Ozone Action Day Alerts.

Section 2: Time series plots of hourly measurements

Most recent quality-assured monthly data acquired at the NR-AQM-01 monitoring site are made available by TxDOT in the form of displayed graphs but also in a downloadable format. Graphs can be saved and/or printed by the user as well. The purpose is to inform the public about the near-road pollution levels during and after the NHHIP construction project.

PM2.5 24-hr concentrations

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.

NO2 hourly concentrations

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.
  4. The complete dataset for all NO2, NO, and NOx concentrations can be found in the April 2024 NR-AQM-01 hourly NOx concentrations

CO hourly concentrations

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.

Temperature and relative humidity hourly measurements

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.

Wind speed and direction hourly measurements

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.

VOCs 24-hr average concentrations

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.

VOCs 24-hr AMCV percentages

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