8.1.5 Precipitation
For
areas where precipitation falls in a frozen form, consideration should be
given to ordering an electrically heated rain and snow gauge. AC power must
be available to the precipitation measurement site. For remote sites where
AC power is not available, propane-heated gauges can be ordered. However, if
air quality measurements are being made at the same location, consideration
should be given to the air pollutant emissions in the propane burner
exhaust.
Air
movement across the top of a gauge can affect the amount of catch. For
example, Weiss [64] reports that
at a wind speed of 5 mph, the collection efficiency of an unshielded gauge
decreased by 25%, and at 10 mph, the efficiency of the gauge decreased by
40%. Therefore, it is recommended that all precipitation gauges be installed
with an Alter-type wind screen, except in locations where frozen
precipitation does not occur.
Exposure
is very important for precipitation gauges; the distance to nearby
structures should be at least two to four times the height of the structures
(see Section 3.1.3). Adequate lengths of cabling must be ordered to span the
separation distance of the gauge from the data acquisition system. If a
weighing gauge will be employed, a set of calibration weights should be
obtained.
8. QUALITY ASSURANCE AND QUALITY CONTROL
8.1 Instrument Procurement
8.1.1 Wind Speed
8.1.2 Wind Direction
8.1.3 Temperature and Temperature Difference
8.1.4 Dew Point Temperature
8.1.5 Precipitation
8.1.6 Pressure
8.1.7 Radiation
8.2 Installation and Acceptance Testing
8.2.1 Wind Speed
8.2.2 Wind Direction
8.2.3 Temperature and Temperature Difference
8.2.4 Dew Point Temperature
8.2.5 Precipitation
8.2.6 Pressure
8.2.7 Radiation
8.3 Routine Calibrations
8.3.1 Sensor Check
8.3.2 Signal Conditioner and Recorder Check
8.3.3 Calibration Data Logs
8.3.4 Calibration Report
8.3.5 Calibration Schedule/Frequency
8.3.6 Data Correction Based on Calibration Results
8.4 Audits
8.4.1 Audit Schedule and Frequency
8.4.2 Audit Procedure
8.4.3 Corrective Action and Reporting
8.5 Routine and Preventive Maintenance
8.5.1 Standard Operating Procedures
8.5.2 Preventive Maintenance
8.6 Data Validation and Reporting
8.6.1 Preparatory Steps
8.6.2 Levels of Validation
8.6.3 Validation Procedures
8.6.4 Schedule and Reporting
8.7 Recommendations