Air quality in Colombo has significantly worsened over the past three months. Measurements using the Air Quality Index (AQI), which is based on PM2.5 levels, show a marked decline since November 2024. While conditions were considered “Good” in early October 2024, by December they had reached “Unhealthy ” levels.
In October 2024, Colombo’s air quality remained stable. The weekly average AQI stayed firmly within the “Good” range (0–50), and even the highest hourly values only reached the “Moderate” level (50–100). This meant consistently clean air and no health risks for anyone.
However, from November 2024 onwards, conditions began to worsen. The weekly average AQI rose into the “Moderate” range, and on some days, the highest AQI readings entered the “Unhealthy for Sensitive Groups” category (100–150). These short-term spikes were serious enough to affect those with existing health conditions.
By December 2024, air quality had deteriorated further. By the end of the month, the weekly average was nearing the upper range of the “Unhealthy for Sensitive Groups” category, while the highest hourly levels had reached the “Unhealthy” range for everyone. During these periods, air pollution posed a real health threat to the entire population.
Such high pollution levels indicate rising concentrations of harmful particles like PM2.5, which can affect health even after brief exposure. Poor air quality can trigger or worsen breathing and heart problems, especially among vulnerable groups such as children, older adults, and those with existing medical conditions.
Colombo’s increasing AQI highlights the importance of regularly monitoring air quality and taking preventive steps—both at individual and policy levels. This worsening trend is a clear warning sign that urgent, collective action is needed to improve air quality and protect public health.
Note: The AQI is calculated based on particulate matter (PM2.5) concentrations in the air. For details on how air quality is measured and categorised, refer to our previous blog. To convert PM2.5 levels into AQI values, recent standard breakpoints and calculations defined by the US Environmental Protection Agency (EPA) are used. This infographic displays the weekly average AQI as a line, offering a clearer picture of overall trends by smoothing out daily changes. The shaded area indicates the range of hourly AQI values (from minimum to maximum) recorded each week, illustrating the full spectrum of air quality conditions over that period.
Research by: Akshayvisnu Ramanathan and Anushan Kapilan
Visualisation by: Muaadh Himaz