Industrial activities and transportation sources contribute significantly to the emission of volatile organic compounds VOCs in urban areas. VOCs are a group of carbon-containing compounds that easily evaporate at room temperature. They are emitted from various sources, including industrial processes, vehicle exhaust, fuel combustion, and consumer products.1. Industrial activities: Industries such as chemical manufacturing, petroleum refining, and paint production release large amounts of VOCs into the atmosphere. These emissions occur during the manufacturing, storage, and transportation of chemicals, solvents, and other products. Some common industrial VOCs include benzene, toluene, ethylbenzene, and xylene.2. Transportation sources: Vehicles, especially those powered by gasoline and diesel engines, emit VOCs through their exhaust. The main VOCs emitted by vehicles are benzene, toluene, ethylbenzene, and xylene. Additionally, VOCs are released during the evaporation of fuels, such as gasoline, from storage tanks, refueling stations, and vehicle fuel systems.Impact on indoor and outdoor air quality:1. Outdoor air quality: The release of VOCs from industrial activities and transportation sources contributes to the formation of ground-level ozone and secondary organic aerosols SOAs . Ground-level ozone is a major component of smog and is formed when VOCs react with nitrogen oxides NOx in the presence of sunlight. Ozone is a harmful air pollutant that can cause respiratory problems, aggravate asthma, and reduce lung function. SOAs are tiny particles that can penetrate deep into the lungs, causing respiratory and cardiovascular issues.2. Indoor air quality: VOCs can also infiltrate indoor environments through ventilation systems, infiltration, and the use of consumer products containing VOCs e.g., cleaning agents, paints, and adhesives . High concentrations of VOCs indoors can cause various health problems, including headaches, dizziness, eye, nose, and throat irritation, and in some cases, long-term exposure can lead to chronic health issues such as liver and kidney damage or cancer.To mitigate the impact of VOC emissions from industrial activities and transportation sources, it is essential to implement stricter emission regulations, promote cleaner technologies, and encourage the use of alternative fuels and public transportation. Additionally, improving indoor air quality can be achieved by using low-VOC products, ensuring proper ventilation, and regularly maintaining HVAC systems.