Mechanism of acid rain

1.	Mechanism of acid rain
Answer» This is due to the presence of acidic oxide emissions in the atmosphere from industries and vehicles. However, a rainfall that has a pH value of less than 5.6 is considered as acid rain . It is formed when sulphur dioxides and nitrogen oxides, as gases or fine reacts with rain water.Local soil was generally alkaline; atmospheric aerosols, which are mixtures of stirred-up soil particles and anthropogenic pollution, were slightly acidic, cloud condensation nuclei, which initiate clouds at condensation level, had an average pH of ∼6. However, local clouds were very acidic (pH ∼4), indicating that further acidification takes place in clouds by adsorption of acidic gases, e.g., CO2, SO2, and NOx. We found that summer showers formed by coalescence of cloud droplets are likely to be as acidic as cloud water.If the snow crystals are initiated by freezing of cloud droplets and grow by vapor diffusion, then the constituents of cloud water are diluted and the snow is less acidic than cloud water. If snow grains (graupel) are formed by accretion of frozen cloud drops or by riming, the snow can be as acidic as cloud water. Both atmospheric chemical reactions and cloud microphysical processes are responsible for chemical variations in precipitation.

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