The correct use of the time zone adjustment factor (parameter tadjust) required by the US EPA AERMET meteorological preprocessor often causes some confusion. The incorrect use of this parameter may lead to a failed AERMET run or incorrect output.
The Time Zone Adjustment Factor (tadjust) is an adjustment factor that is subtracted from the reported hour to convert the time to local standard time. The parameter tadjust should be specified in the AERMET Input File for the following:
Hourly surface data file
Upper air data file
Onsite data file / Application site
HOURLY SURFACE DATA
The hourly surface data in AERMET requires the following adjustment:
Several of the data file formats accepted by AERMET are recorded in local time – i.e., the same time zone which the meteorological station is located. This means that the adjustment to local time for surface data will be zero.
The exception is the TD-3505 / ISHD format which is recorded in GMT. For stations using this format, the modeler must supply the number of time zones west (positive number) or east (negative number) of GMT.
AERMET View Surface Pathway Time Zone Setting – Data Recorded in LST
AERMET View Surface Pathway Time Zone Setting – Data recorded in GMT
The Time Zone Adjustment Factor is input to the AERMET Stage 1 input file, under the Surface LOCATION keyword, following the Latitude and Longitude parameters as follows:
LOCATION 24157 47.633N 117.533W 0
UPPER AIR DATA
The upper air data in AERMET requires the following adjustment:
Typically, upper air data is recorded in GMT (Greenwich Mean Time), which means that in most cases the adjustment to local time will be a non-zero value.
AERMET View Upper Air Pathway Time Zone Setting
The Time Zone Adjustment Factor (tadjust) is entered in the AERMET Stage 1 input file, under the Upper Air LOCATION keyword, following the Latitude and Longitude parameters as follows:
LOCATION 00024157 47.633N 117.533W 8
Note that the above example is for a station located in the Pacific Time Zone (GMT -8). For stations west of Greenwich, a positive number should be specified (e.g., for GMT -8 the adjustment is 8). For stations east of Greenwich, a negative number should be specified (e.g., . for GMT +8 Beijing, the adjustment is -8).
ONSITE DATA / APPLICATION SITE
When supplying an onsite data file to AERMET, location information is also provided. This includes a Time Zone Adjustment Factor:
The Time Zone Adjustment Factor (tadjust) is entered in the AERMET Stage 1 input file, under the Onsite LOCATION keyword, following the Latitude and Longitude parameters as follows:
LOCATION SiteID 47.633N 117.533W 0
In addition, for cases where mixing height data are input via the Onsite Pathway in place of using Upper Air data, this LOCATION card is also written to the AERMET Stage 3 input file.