What causes a brown hazer near cities?

Brown haze near cities is primarily caused by the accumulation of air pollutants, including nitrogen oxides (NOx), volatile organic compounds (VOCs), and particulate matter. These pollutants result from vehicle emissions, industrial activities, and the burning of fossil fuels. When sunlight interacts with these pollutants, it leads to the formation of ground-level ozone and secondary particulate matter, which contribute to the brownish tint in the atmosphere. Weather conditions, such as temperature inversions, can exacerbate this haze by trapping pollutants close to the ground.