The Effect Of Heavy And Sustained Rains On Fallout Dust Monitoring
During weather of this type we note:
General dust levels of agricultural, topsoils or other environmental dusts are lower due to the sources being saturated rather than the water droplets milking out the airborne dust.
Production dust, however, is not greatly affected as any crushing, blasting or milling operation will still generate dust.
Because of the above 2 factors the content of fallout dust will now have higher production dust as a percentage content but less in terms of the total dust concentration (the agricultural soil dust is almost non-existent).
Organic debris will be lower as well.
Pulverised roadway generated dusts will be lower or almost absent except where heavy traffic dried the surface.
The sustained rainy & wet conditions have been extensively studied in the Western Cape area which has such rains during winter periods.
Results can be in the order of 5-10% of the normal dry weather dust conditions.
The recovery of dust levels will take some time as roads & dusty areas will need to dry out before the dust levels start to increase again.
During the “recovery” period the first thing that increased is the organic debris & insect debris.
During extended heavy rain periods the addition of algaecides needs to be increased as the acidic rain addition will encourage the development of algae & other bacterial colony growth. Fortunately these do not add a lot of mass to each sample, but as a percentage this organic material increases a lot as the overall mass remains low.
Due to the increased humidity of the air production dust will not travel as far as the air density is lower & cannot thus support dust with the result that the precipitation rate gradient is steeper ie. Production dust from a crusher installation will perhaps all precipitate out within 80-100metres (no wind) while in dry weather the material fines could still be in suspension at half a kilometre.
The d0.50 average particle size of production dust at a given DustWatch position will be finer.
Remember acid + base = salt & therefore the salinity of the water will increased. This fortunately does not add mass to the sample.