Understanding the Air Quality Index (AQI) Gases

The Air Quality Index (AQI) is a tool used to communicate how polluted the air currently is or how polluted it is forecast to become. It focuses on health effects that can be experienced within a few hours or days after breathing polluted air. In India, the National Air Quality Index monitors several key pollutants.

The question asks which atmospheric gases from the given list are normally considered when calculating the AQI in cities in our country. Let's look at the gases provided:

• Carbon dioxide ($\text{CO}_2$)
• Carbon monoxide ($\text{CO}$)
• Nitrogen dioxide ($\text{NO}_2$)
• Sulfur dioxide ($\text{SO}_2$)
• Methane ($\text{CH}_4$)

Which Gases are Included in AQI Calculation?

The standard pollutants monitored for AQI calculation in India typically include:

• Particulate Matter (PM2.5 and PM10)
• Ozone ($\text{O}_3$)
• Nitrogen dioxide ($\text{NO}_2$)
• Sulfur dioxide ($\text{SO}_2$)
• Carbon monoxide ($\text{CO}$)
• Ammonia ($\text{NH}_3$)
• Lead ($\text{Pb}$)

Now let's examine the gases listed in the question against this standard list of AQI pollutants:

• Carbon dioxide ($\text{CO}_2$): Carbon dioxide is a primary greenhouse gas and a major contributor to climate change. While important for the environment, it is generally not included in the standard daily Air Quality Index calculations which focus on pollutants with more immediate health impacts at typical ambient concentrations.
• Carbon monoxide ($\text{CO}$): Carbon monoxide is a poisonous gas produced by the incomplete burning of carbon-based fuels. It is a standard pollutant monitored for AQI because it can affect the amount of oxygen carried in the bloodstream, posing health risks.
• Nitrogen dioxide ($\text{NO}_2$): Nitrogen dioxide is a gas that primarily gets into the air from the burning of fuel. It is a significant air pollutant, contributing to respiratory problems and the formation of smog and acid rain. It is included in AQI monitoring.
• Sulfur dioxide ($\text{SO}_2$): Sulfur dioxide is produced when fuels containing sulfur are burned, like coal and oil. It can cause respiratory issues and contributes to acid rain. Sulfur dioxide is a standard pollutant monitored for AQI.
• Methane ($\text{CH}_4$): Methane is a powerful greenhouse gas and a component of natural gas. Like carbon dioxide, its primary concern is related to climate change, and it is not typically included in the standard daily Air Quality Index calculations focused on immediate health impacts.

Identifying the Correct Gases for AQI

Based on the standard components of the Air Quality Index calculation, the gases from the given list that are normally considered are Carbon monoxide ($\text{CO}$), Nitrogen dioxide ($\text{NO}_2$), and Sulfur dioxide ($\text{SO}_2$). These correspond to points 2, 3, and 4 in the question's list.

Therefore, the correct combination of gases from the list that are normally considered for calculating the Air Quality Index is Carbon monoxide, Nitrogen dioxide, and Sulfur dioxide.

Revision Table: AQI Pollutants

Additional Information on Air Quality

The Air Quality Index value is calculated based on the concentration of these pollutants in the air. A higher AQI value indicates poorer air quality. Different countries and regions may include slightly different sets of pollutants or use different calculation methods, but the gases mentioned (CO, NO₂, SO₂) are commonly included in many systems, including India's.

Monitoring these specific gases and particulate matter is crucial because they have known adverse effects on human health and the environment even with short-term exposure at elevated concentrations. Greenhouse gases like Carbon dioxide and Methane are primarily monitored for their long-term impact on climate rather than short-term air quality health effects, which is the focus of the daily AQI.