The fading luster of metallic heritage in the Kathmandu Valley is primarily caused by air pollution, particularly from vehicle emissions and industrial activities. The presence of pollutants, such as sulphur dioxide (\(\rm SO_{2}\)) and nitrogen oxides (NOx), can lead to the formation of acidic compounds that corrode metals, tarnishing their surface and deteriorating their appearance over time.

One chemical equation that illustrates the impact of air pollution on metallic surfaces is the reaction of sulfur dioxide with oxygen and water to form sulphuric acid.

\(\rm SO_{2}\) + \(\rm O_{2}\) + \(\rm H_{2}O\) → \(\rm H_{2}SO_{4}\)

\(\rm H_{2}SO_{4}\) further corrodes metals. For eg: When \(\rm H_{2}SO_{4}\) reacts with a metal, such as copper (Cu), it can lead to corrosion of the metal.

\(\rm Cu\) + \(\rm H_{2}SO_{4}\) → \(\rm CuSO_{4}\) + \(\rm H_{2}\)

In this reaction, the copper metal is corroded by the sulphuric acid, leading to the formation of copper sulphate, which can further contribute to the deterioration of metallic heritage.