In general, marbles that make palaces, other monuments and forms of architecture, limestone and natural sources of ammonia are severely affected by the action of oxides of sulphur($SO _2$).
The passage of $SO _2$ gas has caused the yellowing of Taj Mahal over these years.

The Taj Mahal has become a matter of concern because pollutants in air are discolouring its white marble. It is the most beautiful place in India and it will be a tragedy if something bad happens to it. 

Experts have warned that pollutants in the air are discolouring its white marble. So, it is not only living organisms that get affected by polluted air but non-living things like buildings, monuments and statues also get affected.

The Supreme Court ordered industries to switch to cleaner fuels like CNG (Compressed Natural Gas) and LPG (Liquefied Petroleum Gas). Moreover, the automobiles should switch over to unleaded petrol in the Taj zone.

Experts have warned about Taj Mahal that pollutants in air are discolouring its white marble.

Granite is the least susceptible to acid rain because its it is composed of feldspar and quartz, both of which resist attacks of acid.

Sulphur dioxide fumes mix with air moisture and come down as acid rain in the form of sulphuric acid. This acid rain can damage the marble tombs which is calcium carbonate and its reaction with acid rain forms calcium sulfate which gives a yellowish color of acid to the marble. This gradually destroys the marble structure over a period of time.
$CaCO _3 + H _2SO _4 \rightarrow CaSO _4 + H _2O + SO _2\uparrow$

$CO _2$ which is naturally occurring oxide dissolves in water and form carbonic acid and makes the normal rain water slightly acidic.

Acid rain corrodes the marble of the monument. The phenomenon is also called Marble cancer.

Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions. Acid rain pollutes water and soil. It can have harmful effects on plants, aquatic animals and infrastructure.

Acid rain is very harmful as it contains sulphuric acid and nitric acid. It reduces the fertility of soil, damages vegetation and affects the marble monuments by corrosion.

All the above activities result in the less use of fossil fuels, and hence less release of acid rain causing oxides.

Since the area in which Taj Mahal is located is surrounded by many industries and factories, they emit a great amount of pollutants into the atmosphere, They even release toxic and acidic components in the near by water bodies. The pollutants in air are discoloring the white marbles of Taj Mahal due to acidic corrosion (caused by the oxides of non-metals like sulfur and nitrogen).

When pH of rain water drops anywhere below 5.6, it is said to be acid rain. 

One of the most fundamental acid rain solutions is to utilize fuels that burn more cleanly or to burn coal more efficiently. This will greatly reduce the possibilities of acid rain developing in the atmosphere.

The industries located in and around Agra like rubber processing, automobile, chemicals and especially Mathura Oil Refinery have been responsible for producing pollutants like sulphur dioxide and nitrogen dioxide, which contaminate the environment by producing dissolved acids in the air.  

Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids.