The key difference between classical smog and photochemical smog is that classical smog forms due to humid climate, whereas photochemical smog forms due to smoke coming from automobiles and factories.
The term smog can be described as fog or haze intensified by smoke or other atmospheric pollutants. Smog is a type of intense air pollution. This term came into fame in the 20th century. Initially, this term was used to name the pea soup fog, a serious problem in London that occurred from the 19th century to the mid-20th century. This visible air pollution included nitrogen oxides, sulfur oxide, ozone, smoke, and some other particulates.
We can categorize it into classical smog and photochemical smog based on their formation. In addition, we can also categorize smog as summer smog and winter smog. Summer smog is associated with the photochemical formation of ozone. Winter smog forms in the winter season; it occurs when the temperatures are colder and atmospheric inversions are common, which causes an increase in coal and other fossil fuel usage that is important in heating homes and buildings.
What is Classical Smog?
Classical smog is a mixture of smoke, fog, and sulfur dioxide that forms as a result of a cool, humid climate. A classical smog tends to undergo a reduction in nature. We can find this type of natural smog in areas having a humid climate. Classical smog can act as a reducing agent in the presence of atmospheric pollution; therefore, we call it a reducing smog.
What is Photochemical Smog?
Photochemical smog or summer smog is the chemical reaction of sunlight, nitrogen oxides, and volatile organic compounds in the atmosphere. This reaction leaves airborne particles and ground-level ozone. This type of smog depends on primary pollutants and the formation of secondary pollutants.
Primary pollutants include nitrogen oxides such as nitric oxide and nitrogen dioxide, volatile organic compounds, etc. Secondary pollutants include peroxyacetyl nitrates, tropospheric ozone, and aldehydes.
Moreover, the composition of photochemical smog and the reactions involved in the formation of it were not completely understood until the 1950s.
There can be some natural causes that result in photochemical smog. The major natural sources include volcanoes and plants. Usually, an erupting volcano emits a high level of sulfur dioxide along with a large amount of particulate matter it emits. These two are the key components in forming a photochemical smog. The photochemical smog formed as a result of volcanic eruption is named “vog”. This helps us to distinguish it as a natural occurrence. The second major source of photochemical smog is the plants. Globally, plants and soil contribute to the production of hydrocarbons by producing isoprene and terpenes. These hydrocarbons that are released from the plants tend to be highly reactive than man-made hydrocarbons. These compounds can cause the formation of photochemical smog.
What is the Difference Between Classical Smog and Photochemical Smog?
The key difference between classical smog and photochemical smog is that classical smog forms due to humid climate, whereas photochemical smog forms due to smoke coming from automobiles and factories. Moreover, classical smog forms in cool, humid climates, while photochemical smog forms in dry and sunny climates.
The below infographic presents the differences between classical smog and photochemical smog in tabular form for side by side comparison.
Summary – Classical Smog vs Photochemical Smog
The term smog can be described as fog or haze intensified by smoke or other atmospheric pollutants. Classical smog forms as a result of natural incidents, while photochemical smog forms as a result of human activities. The key difference between classical smog and photochemical smog is that classical smog forms due to humid climate, whereas photochemical smog forms due to smoke coming from automobiles and factories.
1. “What Is Photochemical Smog? Formation and Causes with Faqs.” BYJUS, 16 Apr. 2020.