Technical Services Branch
Routine Ambient Air Monitoring Activities

Routine Monitoring Schedule

• SO2, CO, 03, NO2, are monitored continuously
• Particulate matter (PM- 10), and lead are monitored for 24-hour periods, once every six days (this sampling schedule is observed nationwide)

Routine station operations and Quality Assurance Control Measures

• Once a day
  • A member of the Technical Services Branch's staff visits each station and the operation of the monitors is checked. The premises are also checked for any vandalism or changes in nearby emissions activities that might account for unusually high or atypical instrument readings.
  • Any required routine maintenance (e.g. changing of filters or cleaning of sample lines, cleaning inlet probe, etc.) is performed during this daily visit.
• Once every two weeks
  •  The response of each instrument is challenged at both the high and low ends of their measurement range. The   check at the low end is referred to as the precision check, and the check at the high end is the span check.
  • To perform a precision and span check, calibration gases of certified concentrations are introduced into the instruments sampling inlet and the response is recorded. The response must be within a specified limit (varies for each pollutant, generally ± 1O% of true value) or the instrument must undergo a full re-calibration.
• Once every quarter
  • For the entire monitoring network, one instrument for each pollutant is singled out for independent calibration check or audit. This audit is carried out by someone other than the staff member carrying out the routine precision and span checks and is also carried out with an independent set of calibration gases. If an instrument fails the audit, it must undergo a full re-calibration by the routine station operator and the audit is repeated.
• At least once per year
  • Through participation in EPA's National Performance Audit Program, every instrument in the monitoring network is subjected to an audit through use of EPA supplied primary calibration standards and calibration devices. This audit serves as an independent check on the District's calibration and maintenance procedures. Instruments failing these audits are subjected to full re-calibration.

Data Reporting

• All data collected at each, monitoring station is submitted to the U.S. EPA Aerometric Information Retrieval System Air Quality Subsystem (AIRS-AQS) on a monthly basis for continuous gaseous pollutants (CO, 03, S02, N02) and on a quarterly basis for particulate matter (PM-10 and Lead). Also submitted quarterly are the results of all audits and precision and span checks.
• Daily measurements taken each morning and afternoon are reported to the Metropolitan Washington Council of Governments for the purpose of determining the area's daily Air Quality Index (AQI).