The higher concentration of which gas in air can cause stiffness of flower buds?

Pollution results from the presence of dangerous substances in the atmosphere. Air pollution is caused by human activities such as the burning of fossil fuels, smoke from factories, thermal power plants, etc. Nitrogen oxide and carbon monoxide are byproducts of combustion. These gases help to pollute the air. Acid rain is created when water vapor, sulphur dioxide, and nitrogen oxides from the atmosphere combine to make nitric acid or sulfuric acid. Therefore, a high concentration of sulphur dioxide, or ${\mathrm{SO}}_2$, in plants as a result of acid rain causes the flower buds to stiffen and fall off, which interferes with the plant's reproductive cycle.