Acid RainAcid rain is rain that is highly acidic because of sulphur oxides, nitrogen oxides, and other air pollutants dissolve in it. Normal rain is slightly acidic, with a pH od 6. Acid rain may have a pH value as low as 2.8.

Acid rain can severely damage both plant and animal life. Certain lakes for example, have lost all fish and plant life because of acid rain.

Acid rain comes from sulphur in coal and oil. When they burn, they make sulphur dioxide (SO2). Most sulphur leave factory chimney as the gaseous sulphur dioxide (SO2) and most nitrogen is also emitted as one of the nitrogen oxides (NO or NO2), both of which are gases. The gases may be dry deposited-absorbed directly by the land, by lakes, or by the surface vegetation. If they are in the atmosphere for any time, the gas will oxidise (gain an oxygen atom) an go into solution as acids.

Sulphuric acid (H2SO4) and the nitrogen oxides will become nitric acid (HNO3). The acids usually dissolve in cloud droplets and may travel great distance before being precipitated as acid rain. Catalysts such as hydrogen peroxide, ozone and ammonium help promote the formation of acids in clouds. More ammonium (NH4) can be formed when some of the acids are partially neutralized airborne ammonia (NH3). Acidification increases with the number of active hydrogen (H+) ions dissolve in acid. Hydrocarbons emitted by for example car exhaust will react in sunlight with nitrogen oxides to produce ozone. Although it is invaluable in the atmosphere, low level ozone causes respiratory problems and hastens the formation of acid rain. When acids rain falls on the ground it dissolved and liberates heavy metals and aluminium (Al). when it is washed into lakes, aluminium irritates the outer surface of many fish. As acid rain falls or drains into the lake the pH of the lakes falls. Forest suffer the effect of acid rain through damage to leaves, through the lost of vital nutrients and through the increased amount of toxic metals liberated by acid, which damage roots and soil microorganism.

the gases may be drying deposited absorbed directly by the land,by lakes or by the surface "vegetation"

1. what is the definition of the underlined word?

2.what harms respiratory organs?