气象和空气质量监测

CR23X integral in the study of proposed power plantsites
Tall tower platforms help record baseline data

The past few years have seen a scramble within the powerindustry to use more of Utah's natural resources for electric powerproduction.  To secure the required permits to constructproposed facilities, power companies must model emissions from theproposed plant site using cur-rent meteorological and air qualitydata that are representative of on-site conditions. Meteorological Solutions, Inc. (MSI) installed and operatedmeteorological and air quality monitoring systems to characterizebaseline conditions at proposed or existing power plant locationsin Utah.  A minimum of one year of valid data is required, andstrict quality control measures are implemented to assure high datarecovery.  Data are collected and stored as 15-minute averagescomputed from 1-second values using a Campbell Scientific CR23X datalogger.  A reliable landline or cellular telephoneconnection allows frequent interrogation of the installeddataloggers to retrieve data and confirm data validity. Campbell Scientific's Datalogger Software was used for dataretrieval, real-time display of numeric values, and dataloggerprogram modifications.

View of two deployed instrument platforms frombelow; the wind speed, wind direction, and aspirated temperaturesensors can be distinguished.

For all of these applications, meteorological sensors wereeither mounted on 50 or 100 meter towers.  Wind andtemperature sensors were boom-mounted on electrically poweredinstrument lift carriages at 100 or 50 meters and at 10meters.  This feature facilitated sensor access for periodicmaintenance and semi-annual performance audits and eliminated theneed to climb the towers.  The tower sensor configurationincluded MetOne 010C/020C sensors to measure wind speed anddirection at 10 and 50 or 100meters and R.M. Young RTD temperatureprobes with motor-aspirated shields at 2, 10, and 50 or 100 meterlevels.  This arrangement allowed for a variety of deltatemperature calculations to satisfy differ-ent dispersion modelinput requirements. A Li-Cor LI200X measured solar radiation and aVaisala CS105 measured barometric pressure.

View of the base of a 50 meter tower; power plantis in the background.

All towers were instrumented with sensors to collect data forinput into the EPA-approved ISCST dispersion model. Two towers wereequipped with additional sensors to satisfy the data inputrequirements of the EPA-approved AERMOD and CALPUFF dispersionmodels.  These included the Vaisala HMP45C sensor for relativehumidity, the REBS Q-7.1 Net Radiometer, and the R. M. Youngtipping bucket rain gauge.

Atmospheric stability was calculated using three differentmethods.  Sigma theta(σθ) was calculated by the CR23X from1-second data and stored every 15 minutes for later calculation ofatmospheric stability using the sigma theta method.  The solarradiation-delta temperature (SRDT) approach to calculatingatmospheric stability required processing the 15-minuteaverage databy MSI as did the sigma-W approach which uses vertical wind speedmeasurements.

In order to maintain current information about site measurementsystems and assure high rates of data recovery (usually greaterthan 98%), dataloggers were interrogated daily whenever possibleusing either the COM210 telephone modems or a COM100 cellular phonepackage.  After interrogating the on-site datalogger andretrieving all data stored since the last call, MSI computers inSalt Lake City stored the data.  The data validation processwas initiated when these data were automatically subjected to aseries of parameter-specific quality tests using a programdeveloped by MSI based on USEPA guide-line criteria.  Theprogram generated are port identifying each value in the data filethat failed one or more of the listed tests.  In addition, aseries of stacked time parameter plots were created so that an airquality meteorologist could visually inspect or look forirregularities in the data, assess parameter inter relationships,and decide if corrective action was needed. If appropriate, thesite technician was dispatched to the site as soon as possible torectify the problem.

As an added quality control measure to confirm proper operationof motor-aspirated temperature shields, the shields were equippedwith flow switches that were interfaced with control ports ontheCR23X.  Whenever the flow through the aspirated shields wasobstructed (e.g., by icing or spider webs), a switch connected tothe control port prompted the datalogger program to increment acounter.  The quality control program registered the counts asa parameter that failed the data editing criteria, and the sitetechnician initiated corrective action.

The ENC 16/18 enclosure functions as an “on-siteheadquarters;” the CR23Xenables quality control, performs datacalculation, and provides communications through a COM200.

Quality control for atmospheric gas sampling equipment mayinclude periodic zero, span and precision checks. The checks can beactivated by the CR23Xcontrol ports connected to an A21REL-12relaydriver and interfaced with the gas analyzer calibrationsystem.  Gas analyzers and calibrators with RS-232 connectionsto their microprocessors allow remote access via modem to theirsystems.  At one air quality monitoring station, MSI used acode-activated switch for selectable telephone access of not onlythe CR23X but the gas monitoring equipment as well. This featureallowed real-time communication with the analyzer to viewdiagnostics and troubleshoot problems remotely.