What factor does NOT affect flowering in plants?

Flowering in plants is primarily influenced by environmental factors such as light duration, temperature, and sometimes water and nutrient availability. Photoperiod, or the length of day versus night, is a critical factor for many plants, as it helps them determine the right time to bloom based on the seasonal light changes. Soil type can also be significant, as different soils provide varying levels of nutrients and support for root systems, which can indirectly affect flowering. Water availability plays a crucial role as well, since plants require adequate moisture for optimal growth and reproduction, including blooming.

Air pollution levels, however, do not directly influence the biological mechanism that governs flowering in plants. While pollution can have adverse effects on plant health and growth, it does not alter the fundamental processes that control flowering, such as photoperiod sensitivity or hormonal responses. Therefore, among the options given, air pollution levels are less likely to be a determining factor in the flowering process of plants, making it the correct choice for this question.