Photochemical smog (smoke + fog) is a type of pollution that is created when ultraviolet light reacts with NOx (nitrogen oxides) and VOC’s (volatile organic compounds) which are found in the atmosphere. This can only occur when there is sunlight and is most prominent in the morning and afternoon. Warm sunny days with gentle winds and a lower level inversion combined with the pollutants derived from the combustion of hydrocarbon and NOx cause this to happen. Even though the combustion of hydrocarbons and NOx is mostly omitted from the burning of fossil fuels, these pollutants can also be sourced from volcanic eruption, and forest fires.
When broken down, photochemical smog occurs when nitrogen and oxygen combine in the combustion process to form nitric oxide. The nitric oxide created oxidizes in the atmosphere to produce nitrogen dioxide. Sunlight breaks down nitrogen dioxide into nitric oxide and an oxygen radical. The oxygen radical combines with molecular oxygen to form ozone. This ozone produced is the main component of photochemical smog.
The result of this photochemical fog is that it visibly lingers in the air causing a haze in the air. This smog can cause detrimental effects on the human respiratory system and can have serious strain on the heart and circulatory system. These effects cause humans to become mildly sick but can also be as serious as contributing to death.
Photochemical smog can also adversely affect the environment. It can decrease crop production, the termination of photosynthetic plants, and have poor effects on any animal dependent on clean air. Photochemical smog can even corrode hard surfaces that make up buildings and cities.
LA is an ideal place for photochemical smog to occur. It’s low valley creates a good place for the smog to settle once the emissions of its overcrowded car population are created and put into the atmosphere to interact with sunlight. Instead of burning coal to create electricity a better alternative is to combust natural gas because it has cleaner emissions. By limiting the emissions of electricity production, you can directly reduce the photochemical smog occurring. LA created a phasing out of certain pollutants that can be held responsible for the decrease in smog in the area.
Sources
Chameides, W. L., et al. “The role of biogenic hydrocarbons in urban photochemical smog: Atlanta as a case study.” Science241.4872 (1988): 1473-1475.
Tiao, G. C., G. E. P. Box, and W. J. Hamming. “Analysis of Los Angeles photochemical smog data: a statistical overview.” Journal of the Air Pollution Control Association 25.3 (1975): 260-268.