An air quality monitoring network consists of a number of monitoring
stations (e.g. sulphur dioxide and meteorological) including a base station
which captures all the data from the monitoring stations. The outstations
are linked to the base station via a radio frequency network. Each
outstation has its own logger and sufficient storage space for 10 days worth
of data should the communications to the base station be lost. Figure 1
shows a basic view of a typical monitoring network.
Description of Units
Outstations
Outstations refer to the sulphur dioxide monitoring stations as well as the
meteorological stations. Most stations are equipped with a met mast which
houses some kind of a wind monitor, ambient temperature sensor with
radiation shield and the antenna for communication with the base station.
The monitoring stations make use of UV fluorescence analysers to measure
ambient sulphur dioxide concentrations. These stations or shelters are air
conditioned to maintain a temperature between 22 to 30 °C and have to remain
clean and dry.
The instruments in the shelters run constantly and record three minute (3
min) average data. This data is stored in the data logger at the station as
a record and downloaded to the base station when the data logger is polled.
No data is lost when the communication to the base is station goes down. The
data logger continues to store the records until the base station polls the
logger. At this point the logger downloads the latest record first and then
any other records which might be on the logger. It is also possible to
connect the laptop directly to the data logger (Fig 2) to monitor the raw
data capture or to download the outstanding records.
Base station
The Base Station houses the computer network which controls the data
transfer not only within the station but to the outstations as well. The
data flow is shown in figure 2.
Figure 2.
These
monitoring stations can also be equipped to test for other criteria
pollutants besides sulphur dioxide, including ozone, carbon monoxide and
nitrogen oxides.
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