Activity 3.3.1 Air Pollution Core Activity

 Air Pollution Basics

Sulfur Pollutants
Sulfur pollutants include gases like sulfur dioxide (SO2) and hydrogen sulfide (H2S), which come from burning fuels or processing ores that contain sulfur. Once released into the air, SO2 can react, especially in sunlight and moisture, to form sulfate ions and acidic compounds such as sulfuric acid. These create fine particles (aerosols) that reduce visibility (haze) and contribute to acid rain, damaging plant leaves, soils, and aquatic systems. Some plants show visible tissue injury at moderate SO2 levels, while others suffer “hidden injury,” meaning reduced growth without obvious symptoms (Freedman, Chap. 16).

Nitrogen Pollutants
Nitrogen pollutants, often called NOx (nitric oxide, NO, plus nitrogen dioxide, NO2), mainly arise from combustion in vehicles, power plants, and industrial processes. In the atmosphere, NO can oxidize to NO2, which may further convert to nitric acid and nitrate ions in rain or particulate form. These nitrogen compounds contribute to acid deposition, nutrient loading (eutrophication), and help form fine particles that degrade air quality. Another nitrogen gas, N2O, is more inert and has a long atmospheric lifetime, which makes it important for climate. Ammonia (NH3), from soil, fertilizer, and animal waste, also plays a role by often converting to nitrate in the air. While direct injury to vegetation is uncommon at normal levels, the chemical transformations make nitrogen gases very influential (Freedman, Chap. 16).

Hydrocarbon and Volatile Organic Compound Pollutants
Hydrocarbons (chains of carbon and hydrogen) and VOCs (volatile organic compounds) can be emitted naturally by plants and decomposition or from human activities such as fuel combustion, solvents, and evaporation. Although many VOCs at ambient concentrations are not directly harmful to vegetation or humans, they become critically important in air chemistry. In the presence of sunlight, VOCs react with NOₓ in a chain of radical-driven steps (for example, RO2 + NO → NO2 + RO), producing ground-level ozone (O3) and other oxidants. These oxidants damage cell membranes in leaves, reduce photosynthesis, and irritate human respiratory tissues and lungs. Thus, hydrocarbons and VOCs are the central “fuel” for photochemical smog formation (Freedman, Chap. 16).

 

Comparison of Current AQI

First, What is AQI?
The Air Quality Index (AQI) is a scale from 0 to 500 that translates pollutant concentrations into a unified metric. Lower AQI means cleaner air; higher means more health risk. An AQI up to about 50 is “Good” 51–100 is “Moderate” and anything beyond that comes “Unhealthy for Sensitive Groups,”. The purpose is to help everyday people see at a glimpse how air might affect health­­.

At 3:00 pm, Riverside County, California, recorded the highest Air Quality Index (AQI) in the United States at 473, indicating hazardous conditions driven by extremely high particulate matter. In contrast, both San Antonio, TX, and Los Angeles, CA, reported much cleaner air with AQIs of 50, placing them in the moderate range. Ozone readings were available for San Antonio (50) and Los Angeles (44), both well within safe levels, while Riverside had no current ozone data to upload. Overall, the table shows a blunt difference between regions with severe particle pollution and those experiencing only minor or routine levels of air pollution at the same time of day.

Comparison of Current PM 2.5 and O3 (Ozone)

What is PM2.5?
PM2.5 refers to particulate matter with diameter less than or equal to 2.5 micrometers. These fine particles can bypass the nose and throat and reach deep into the lungs and even cross into the bloodstream, causing inflammation, cardiovascular stress, respiratory disease, and contributing to premature death.

What is O3 (ground-level ozone)?
Ground-level ozone is a secondary pollutant formed when NOx and VOCs react under sunlight. Unlike “good” ozone in the stratosphere, this ozone damages lung tissue, leads to coughing and shortness of breath, worsens asthma and lung disease, and impairs plant growth and agricultural yield.

References

Air Now Interactive Map

Freedman, B. (2018). Environmental science: A Canadian perspective. Dalhousie University Libraries.

Texas Commission of Environmental Quality (TCEQ)