UTA TRAX Air Quality Monitoring Dataset Written By: Dr. Alexander Jacques, University of Utah Updated: October 1, 2022 --------------------------- This README describes the format and fields of the measurements observed as part of the UTA TRAX Air Quality Monitoring Study, conducted by the University of Utah and supported by UTA and the Utah Division of Air Quality (DAQ). More information on the project is available via this website (https://atmos.utah.edu/air-quality/trax/index.php). --------------------------- This dataset is divided into monthly compressed comma-delimited files for each measurement platform. As of this writing, there are five different platforms available: TRX01 - Instruments deployed on UTA TRAX Rail Car 1136 TRX02 - Instruments deployed on UTA TRAX Rail Car 1104 TRX03 - Instruments deployed on UTA TRAX Rail Car 1034 RAIL1 - Instruments deployed at a UTA substation around 300 W 1700 S in Salt Lake City (latitude 40.73115 N, longitude 111.89698 W) HAWTH - Instruments deployed adjacent to DAQ equipment at Hawthorne Elementary School (latitude 40.73439 N, longitude 111.87215 W) - Decommissioned December 2021 Platforms installed on the UTA Rail Cars include GPS positioning, train-top ambient temperature and humidity, PM2.5 measurements from a Met One ES-642 Dust Monitor, and ozone measurements from a 2B Technologies 205 Ozone Monitor. Fixed-site platforms RAIL1 and HAWTH contain PM2.5 measurements from Met One ES-642 Dust Monitors. All platforms record sampled measurements from each instrument every 2 seconds. --------------------------- FIELD DESCRIPTIONS Missing observations/fields for a given timestamp are denoted with a -9999 value. The following fields may be seen in the comma-delimited files: Timestamp - The timestamp of the observational record in YYYY-MM-DDTHH:MM:SS format. Observations are recorded in Universal Time Coordinated (UTC), so 7 hours must be subtracted to convert to Mountain Standard Time (6 for Mountain Daylight Time). Latitude - The GPS latitude output (decimal degrees) Longitude - The GPS longitude output (decimal degrees) Elevation - The GPS elevation above sea level output (meters) Battery_Voltage - The battery voltage recorded by the data logging device (volts) Train_Box_Temperature - The temperature recorded inside the installation unit (degrees C) Train_Top_Temperature - The ambient temperature recorded outside of the installation box on top of the rail car (degrees C) Train_Top_Relative_Humidity - The ambient relative humidity recorded outside of the installation box on top of the rail car (percent) ES642_PM2.5_Concentration - The sampled PM2.5 concentration (ug/m3) ES642_Air_Flow_Rate - The air flow rate measured by the ES-642 (L/minute) ES642_Internal_Air_Temperature - The internal temperature of the ES-642 sampled air (degrees C) ES642_Internal_Relative_Humidity - The internal relative humidity of the ES-642 sampled air (percent) ES642_Internal_Air_Pressure - The internal air pressure of the ES-642 sampled air (hectopascals) ES642_Error_Code - The numeric error code recorded by the ES-642 (0 if no errors, integer > 0 if errors indicated) 2B_Ozone_Concentration - The sampled ozone concentration (ppbv) 2B_Air_Flow_Rate - The air flow rate measured by the 2B (L/minute) 2B_Internal_Air_Temperature - The internal temperature of the 2B monitor (degrees C) 2B_Internal_Air_Pressure - The internal air pressure of the 2B monitor (degrees C) PM2.5_Data_Flagged - Binary indication that PM2.5 concentrations should be used with caution (0 or 1 - additional info below) Ozone_Data_Flagged - Binary indication that ozone concentrations should be used with caution (0 or 1 - additional info below) --------------------------- DATA QUALITY CHECKS Numerous automated and manually reviewed data quality checks have been applied to these data to help remove potentially suspicious or inaccurate observations. The unique nature of these deployments on top of electric train cars, which at times share roadways with other vehicles, means that short-term/rapid changes in concentrations could be the result of real signals produced by adjacent vehicles at times. Users are encouraged to inspect data they may use further as well based on their needs (e.g. for temporal or spatial averaging purposes). The following checks have been applied to this dataset: 1) Data are omitted entirely if it has been determined that the train car is located inside a UTA Maintenance Depot or if the GPS is malfunctioning 2) PM2.5 concentrations are set to -9999 if the ES-642 air flow rate falls below 1.5 L/minute or if the concentrations do not pass an unphysical high-frequency noise test. 3) Ozone concentrations are set to -9999 if the 2B air flow rate falls below 1.5 L/minute or if the concentrations do not pass an unphysical high-frequency noise test. 4) PM2.5_Data_Flagged is set to 1 if the ES-642 produces an error code, if the ES-642 internal relative humidity exceeds 50%, or if the ambient train-top relative humidity exceeds 70%. High RH can result in PM2.5 concentrations that are much higher than official measurements when concentrations are elevated (official measurements are heated to remove water). There may be use cases where using this data is still reasonable, which is why it is provided with the flag attribute in place. 5) Ozone_Data_Flagged is set to 1 if the 2B internal temperature or installation unit exceeds 50 degrees C. The performance of the 2B sensors can degrade in extreme heat, so caution should be applied when this is the case.