This phenomenon of photochemical smog & decomposition of Indigo is represented in Figs. 1 and 2 respectively.

Lighter or bleached denims fade faster than basic unwashed denim.

Table 1 & Fig. 3 show the correlation between indigo concentration, ozone concentrations and the extent of fading.

In order to relate laboratory results to actual exposure in a warehouse, a 5-year study was conducted to determine the actual rate of fading under various exposure conditions. The results from these tests are shown in Fig. 3.

2. Air Humidity and Temperature

Higher humidity and higher temperature are known to accelerate yellowing.

High humidity gives a thin water film on denim, which increases the absorption rate of ozone.

High humidity results in higher moisture retention by the denim fabric, consequently increasing the absorption rate of ozone (Table 2).