Pollutant gas deposition is favoured by turbulence and wet surfaces. Aerosols of 0.2 to 1 micron size are the main carriers of acidity and sulphate; Phoretic effects due to condensation (stefan flow) or cold surfaces allow particles to cross the layer of laminar flow. Surface irregularities favour deposition. Rainwater analysis shows that doses of contaminants are low; hydration and mobilization of surface materials deposited before may be more important than direct rain attack. Undiluted plumes may cause high concentration pollution.