The Taj Mahal is threatened by pollution from
SO2
Sulphur dioxide is produced by various industries like rubber manufacturers, sulphuric acid manufacturers, mining and is also emitted by automobiles. Sulphur dioxide is hygroscopic - when it is in the atmosphere, it reacts with humidity and forms sulphuric and sulphurous aerosol acids which combine with other atmospheric pollutants to form acid rain. The air around the Taj Mahal contains dangerously high levels of sulphur and nitrogen oxides. This is due to the large number of industries set up in the neighbourhood, and also pollution of the Yamuna River. As per meteorological studies the wind direction is usually towards the Taj Mahal. All these result in acid rain, which is presently corroding the marble of the monument.