Forming in densely populated urban areas, photochemical smog manifests itself as a brown cloud of fog lingering along the troposphere, subjecting those living in and around the air space to inhale the dense and toxic air it creates. Photochemical smog forms when nitrogen oxides and volatile organic compounds (VOCs) interact with sunlight, forming a light brown haze and creating tropospheric ozone. Photochemical smog in specific comes from automobile emissions, and although ozone is naturally occurring, it is only in the upper atmosphere: if ozone forms at ground-level, it comes at the risk of health issues to humans and other organisms, as well as harming our infrastructure and agriculture.

In terms of human health, nitrogen oxides on their own can cause heart and lung issues, while reducing the immune system response to infections. VOCs cause eye irritation and act as potential human carcinogens. Tropospheric ozone also causes eye irritation, but proves to be harmful to those with pre-existing respiratory conditions: not only does it cause coughing and wheezing, but it can add to the respiratory issues a person is already experiencing, especially for people with asthma. When it comes to infrastructure though, photochemical smog can cause significant damages through weathering. This is possible through acid rain, which is caused by the evaporation of pollutants into the hydrologic cycle. Acid rain has a lower pH balance than normal water, causing it to be more acidic. When acid rain occurs, it corrodes metals and used for buildings and weather stonework, leaving immense damage over a period of time. These damages are expensive and are difficult to repair. 

So what can be done? When it comes to photochemical smog, the city of Los Angeles has been able to find solutions to this issue. L.A. is notorious for its photochemical smog because of the vast number of automobiles in the area. To combat this issue, the California Motor Vehicle Pollution Control Board was created by the California government in 1959, and from there they passed laws allowing for proper emissions tests. Cars were also re-modeled by the 1960s to have a “blowby” in their crankcase that allowed hydrocarbons to re-burn, preventing them from being released into the atmosphere at such a big rate. Later in the 1970s, fuel was also changed. By removing lead from fuel, reduced further pollutants from being emitted, and reduced the risk of further health issues. They also promoted the use of alternative fuels like natural gas or methanol to reduce gasoline usage and emissions. 

References:

Britannica, T. Editors of Encyclopaedia (2019, December 17). Smog. Encyclopedia Britannica. https://www.britannica.com/science/smog

Canada, E. A. C. C. (2010, June 2). Air pollution damage to infrastructure and industry – Canada.ca. Government of Canada. https://www.canada.ca/en/environment-climate-change/services/air-pollution/quality-environment-economy/economic-issues/damage-infrastructure-industry.html

Deziel, C. (2019, March 2). How Is Photochemical Smog Formed? Sciencing. https://sciencing.com/photochemical-smog-formed-6505511.html

Photochemical Smog- what it means for us. (2004, March). U.S. EPA. https://www.epa.sa.gov.au/files/8238_info_photosmog.pdf

The Southland’s War on Smog: Fifty Years of Progress Toward Clean Air (through May 1997). (n.d.). South Coast AQMD. Retrieved December 3, 2021, from https://www.aqmd.gov/home/research/publications/50-years-of-progress#Early%20Smog%20Control%20Efforts