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Question
Why is rain sometimes black in color and what chemical parameters should be
tested?
Case ID : 00203

1) Why is rain sometimes in black color?
2) What chemical parameters should be tested for rain that appears to be black?



From : Safoora, Fathimath
Thailand
Last viewed : 16 September 2019 14:53
Viewed : 3641 (times)



Answers
Answer from expert #1
The most likely cause of rain that looks black is elemental carbon. Chemicals
can be adsorbed onto the surface of carbon particles but it would depend on the
situation as to what chemicals should be monitored.

Answer from expert #2
Rain becomes black in colour if it contains carbon particles from incomplete
combustion of carbon compounds, usually those in fossil fuels but also from
incineration of waste. Apart from carbon particles, such rain may contain
products of incomplete combustion. Some of these may be very toxic but there is
no way of knowing what to look for without knowledge of the material being
burnt. It should be assumed that there will be associated toxicity and the
source of the black particles should be sought and brought under control.

Answer from expert #3
The origin of black soot is normally incomplete combustion of fossil fuel and
burning of biomass. The major component is black soot, but Polycyclic compounds
as well as inorganic ions and metals could be associated with are being part of
the black soot (particulates). The analysis to be performed should include
carbon and perhaps PAHs and depending on the local source of pollution also
sulphate, nitrate as well as selected metals.

Compound specific information can be obtained from the ATSDR webpage.

Answer from expert #4
The origin of black soot is normally incomplete combustion of fossil fuel and
burning of biomass. The major component is black soot, but Polycyclic compounds
as well as inorganic ions and metals could be associated with are being part of
the black soot (particulates). The analysis to be performed should include
carbon and perhaps PAHs and depending on the local source of pollution also
sulphate, nitrate as well as selected metals.

Answer from expert #5
1. Most likely black rain is caused by soot in the atmosphere. Soot particles
are emitted by combustion of fossil fuels, biofuels, and biomass. Black carbon
particles are removed from atmosphere mainly through wash-out in rainfall or
snow.

2. Chemical parameters to be tested include black carbon.

Answer from expert #6
Rain is black if there is soot in the atmosphere due to incomplete combustion.
Collect the soot particles and analyse in the lab.

Answer from expert #7
The 'blackness" is most likely caused by unburnt carbon particles -- black
carbon , from combustion processes.

Besides testing for carbon, sulfates and mercury contents should also be tested.