Final answer:
Photochemical smog comes in two types: industrial, which is gray or black and comes from burning fossil fuels, and photochemical, which is brown and forms from reactions between sunlight and emissions from vehicles and other sources.
Step-by-step explanation:
There are two types of photochemical smog: industrial smog and photochemical smog. Industrial smog primarily comes from burning fossil fuels and typically appears as gray or black in color, resulting from a large amount of particulate matter and sulfur compounds present in it. Photochemical smog, on the other hand, results from chemical reactions between sunlight and pollutants from automobile emissions and other sources. It typically has a brown haze, primarily due to the presence of nitrogen oxides, which can appear brownish when they combine with other air pollutants.
Industrial smog is largely composed of carbon dioxide, carbon monoxides, sulfur compounds, and mercury, which are a result of incomplete combustion processes. On the other hand, photochemical smog forms through a sequence of chemical reactions starting with nitrogen oxides reacting with sunlight, leading to the formation of secondary pollutants like ground-level ozone. This smog is particularly problematic in urban areas with warm, sunny climates, and harms human health, especially affecting senior citizens, children, and individuals with heart and lung conditions.