What Is AQI? How to Understand Air Quality Levels in Nepal

AQI meaning in one sentence

The Air Quality Index is a communication tool that translates measured or estimated pollutant concentrations into a simpler number, color, category, and health message. Higher values represent greater concern for health under the chosen AQI system.

Concentrations use scientific units such as micrograms per cubic metre or parts per billion. AQI makes several pollutants easier to communicate on one scale, but it also hides detail, so the dominant pollutant and raw concentration still matter.

Which pollutants can determine AQI?

AQI systems commonly calculate separate sub-indices for regulated pollutants. The largest sub-index is generally reported as the overall AQI, although the exact pollutants and breakpoints vary by country and platform.

• PM2.5 fine particles
• PM10 inhalable particles
• Ground-level ozone
• Nitrogen dioxide
• Sulfur dioxide
• Carbon monoxide

AQI colors and the action they suggest

Color categories move from lower concern to increasingly unhealthy conditions. Under the widely used US AQI, green is Good, yellow Moderate, orange Unhealthy for Sensitive Groups, red Unhealthy, purple Very Unhealthy, and maroon Hazardous. Other systems may use different thresholds or names.

A category is a prompt to adjust exposure. As pollution rises, reduce duration and intensity, move away from the source, choose cleaner indoor air, and pay closer attention to symptoms. Sensitive people should usually make changes earlier.

AQI is not the PM2.5 concentration

A PM2.5 concentration is the estimated mass of fine particles in a volume of air. A PM2.5 AQI is the index value produced after that concentration is mapped through a particular set of breakpoints and averaging rules. A concentration of 80 micrograms per cubic metre therefore should not be described as AQI 80 without performing the correct conversion.

This distinction also explains why WHO guideline values and AQI category boundaries should not be treated as interchangeable. WHO guidelines are health-based concentration recommendations, while an AQI is a public communication system.

Why two air-quality apps can disagree

A difference does not automatically prove that one platform is wrong. Compare the pollutant concentration, location, timestamp, source type, and AQI standard first. Large or persistent differences should still be investigated.

• They may use different monitoring stations, models, or sensor networks
• Their readings may have different update times or averaging periods
• One may apply calibration or quality-control corrections
• They may use Nepal, US, or another international AQI standard
• One app may report current conditions while another emphasizes a forecast

Common AQI mistakes to avoid

• Treating one reading as representative of every neighborhood
• Ignoring the last-updated time
• Comparing AQI values calculated under different standards
• Assuming a mask removes every gas and particle
• Waiting for symptoms before reducing a clearly avoidable exposure

How to read the VayuDrishti Air Guide

Start with your selected location, current AQI category, dominant pollutant, and timestamp. Next, scan the hourly outlook for a cleaner window. Finally, use the activity guidance for your age, health, and plan. This sequence turns a scientific reading into a practical choice for the day.

Now act

Practical recommendations

• Read the category and health message before focusing on the exact number.
• Confirm which pollutant is responsible for the AQI.
• Check the station or model location and the last-updated time.
• Use the hourly trend to plan activity instead of relying on a single screenshot.
• People in sensitive groups should act earlier and follow their clinician's advice.
• Do not compare two platforms until you know whether they use the same AQI standard and averaging period.