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Tool 16 - Calculating Air Pollution near Industrial Activities
This tool will help the city to set priorities among air pollution problems caused by industries. It consists of a simple table to calculate air pollution at a certain distances from industrial activities. The method of application is described in six steps below.
Based on this tool, UNEP and HABITAT have developed a Spreadsheet to calculate the air pollution caused by all emitting factories in Dar es Salaam (about 35 factories) and the distance from the chimney where the highest concentrations could be expected. This spreadsheet is adaptable to allow cities in developing countries to apply this spreadsheet for their own situations.
The Method:
STEP 1:
Collect the annual emission, the stack height, the heat content, and the
amount of working hours per year of each factory.
STEP 2:
Choose the appropriate correlation factor in the table below:
Table 16.1: Maximum Concentration (in mg/m3) of an Inert Pollutant near an Industrial Source with an Emission of 1 kg/hour, Characterized by Stack Height H (in meters) and Heat Content W (in MW)
*** The data in italics is outside the validity area of the model because the model is not accurate within 100 m of the source. However, it still gives a rough indication of the expected concentrations.
The correlation factors was calculated with the Operational Atmospheric
Transport Model (OPS), a dispersion model for industrial sources developed
by the Dutch National Institute of Public Health and Environment (RIVM).
The correlation factors are based on the general Dutch situation. This
means a wind speed of 4 m/s and a south to west wind direction for about
40% of the time. During the rest of the time, the wind directions are
equally divided.
If the wind speed and directions in your city is not completely different,
this table will give a good indication of the enhanced concentrations
of pollutants near industrial activities. If the wind speed in a specific
city is very different, one must make an assumption about whether the
occurring concentrations will be higher or lower. This method will give
developing countries a good indication of pollution dispersion.
STEP 3:
Calculate the concentration based on the annual emission and the
amount of working hours of each factory.
STEP 4:
The above calculations are based on the assumption that the wind speed
is 4m/sec, and about 40% of wind flows from the southwest. Assess whether
the concentrations will be higher or lower in your individual city.
STEP 5:
Compare the concentration to the (WHO) air quality guidelines for annual
mean SPM concentrations (of 60-90 g/m3).
STEP 6:
Assess the extensiveness of the areas, where the air quality guidelines
are exceeded. The table gives factors to make rough assumptions about
the surface size where guidelines are being exceeded. The Dar es Salaam
example will give an example of how to use the table.
City Example: A Cement Factory in Dar es Salaam
Step 1:
The following data were collected in Dar es Salaam:
* annual emission of the cement factory: 106,000 ton dust (SPM)
* the chimney height: 75 meters
* the heat content: 0 MW (own estimation)
Step 2:
See the correlation factor in the table for 70 - 210 m and 0 MW. The maximum
concentration will be found around 600m from the source, and the concentration
will be
0.03 g/m3 per 1kg SPM/hour.
Step 3: 0.031 g/m3 per 1 kg SPM/hour is the same as:
(0.031/8760)*106,000*1000=375 g/m3 per 106,000 ton SPM/year
Step 4:
The average wind speed in Dar is about 5 to 8 m/sec. Since the city is
situated near the
coast, the dispersion conditions will be better than average. Therefore,
it is expected that
the concentrations due to the emissions of the cement factory will be
somewhat lower than
the calculated 375 ug SPM/m3. We assume that it will be about 300-350
g/m3.
Step 5:
The emissions of the cement factory lead to a serious SPM problem in the
city. The
average calculated concentration at 600m from the source does exceed the
guideline (200-
300 g/m3 versus the guideline of 60-90 g/m3 (WHO) or 200 g/m3 (Indian)).
In all
probability, the concentrations will exceed the WHO guidelines in a large
area around the
cement factory, especially if other sources, e.g., transport, will further
increase the SPM
concentrations.
Step 6:
As calculated in steps 1 to 5, the average calculated concentration at
600m from the source
is seriously exceeding the guideline. Therefore at least 50% emission
reduction is
necessary to reduce the concentrations to the guideline level.
The table in step 6 shows that about 4,440,000 m2 = 4.44 km2 around
the factory will
exceed the guideline (see the factor in the table at a chimney height
of 100m, and a needed
emission reduction of at least 50%).
A spreadsheet with the example of Dar es Salaam City can be opened here for easy adoption by your city.