| Monitoring-site selection and placement | China’s HJ 664-2013, Technical Regulation for Selection of Ambient Air Quality Monitoring Stations (on trial) | Guidance for selecting and locating ambient-air monitoring stations. It is a siting standard, not a general instrument-accuracy tolerance. | Document the sampling location, nearby obstructions, inlet height and surrounding emission sources. Do not treat compliance with HJ 664 as proof of sensor accuracy. |
| Particulate matter: PM2.5 and PM10 | U.S. EPA 40 CFR Part 50, including Appendices J and L for PM10 and PM2.5 reference methods | Defines pollutant-specific reference-method requirements. EPA reference methods for particulate matter use filter-based sampling and laboratory analysis under specified procedures. | Run side-by-side, time-matched sampling with a suitable reference instrument. Report the averaging period, inlet configuration, humidity conditions, data completeness and statistical agreement. A light-scattering sensor should not be described as an FRM-equivalent method without the required evaluation and designation. |
| Ozone (O3) | U.S. EPA 40 CFR Part 50, Appendix D; applicable EPA Federal Reference or Equivalent Method requirements | Specifies a reference photometric method for measuring ozone in ambient air. | Compare simultaneous readings with a properly operated reference analyzer. Record calibration checks, averaging intervals, environmental conditions and results across the intended concentration range. |
| Carbon monoxide (CO) | U.S. EPA 40 CFR Part 50, Appendix C; applicable EPA method designation requirements | Specifies a non-dispersive infrared reference method for ambient CO measurement. | Use a co-located, calibrated reference analyzer and assess bias and precision over representative readings. Check for vibration, power-supply and temperature effects during flight. |
| Sulfur dioxide (SO2) | U.S. EPA 40 CFR Part 50, Appendix A; applicable EPA method designation requirements | Specifies a reference method based on ultraviolet fluorescence for ambient SO2. | Compare against a calibrated reference analyzer, including zero and span checks. Evaluate response time, inlet losses and the effect of flight airflow on sample delivery. |
| Nitrogen dioxide (NO2) | U.S. EPA 40 CFR Part 50, Appendix F; applicable EPA method designation requirements | Specifies a reference method for ambient NO2 measurement using chemiluminescence-based techniques. | Use a reference method appropriate to NO2; distinguish direct NO2 measurement from instruments that infer NO2 through conversion. Document cross-sensitivities and response time. |
| Sampling inlet and aircraft airflow | Instrument-specific sampling design; relevant method requirements for the pollutant being measured | Drone motion, propeller wash, inlet orientation and tubing can change the air reaching a sensor. These effects are not resolved simply by meeting a station-siting standard. | Test the inlet under stationary and representative flight conditions. Record inlet position and orientation, tubing length, flow rate and flight speed; check for particle losses and contamination from the aircraft. |
| Calibration and traceability | Applicable EPA method procedures and the analyzer manufacturer’s validated operating instructions | Reference-method comparisons rely on suitable calibration and documented operating conditions. Requirements vary by pollutant and method. | Keep calibration records, use appropriate standards and document pre-test and post-test checks. Report the reference instrument, calibration status, test dates and any invalid or missing data. |
| Accuracy evidence and reporting | Pollutant-specific EPA FRM/FEM requirements; project-specific acceptance criteria | There is no single universal accuracy threshold that applies to every pollutant, sensor technology or drone configuration. | Publish paired data, sample count, concentration range, averaging period, regression results, bias and precision. State the test conditions and limitations; do not claim EPA reference-method equivalence unless the applicable designation requirements have been met. |
| Practical selection criterion | Combination of intended use, pollutant-specific validation and operational constraints | A suitable system depends on the pollutant, required detection range, sampling duration, flight endurance, payload and whether regulatory-grade measurements are needed. | Choose only after reviewing independent, pollutant-specific collocation results and confirming that the complete drone-and-inlet configuration was tested for the intended operating conditions. |