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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


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