No Fires, So Why the Haze? Calm Winds Are Bad for Urban Cities

Hazy conditions in Singapore in late March were due to unusual atmospheric conditions

- Steve Yim

From March 25 to 27, residents across Singapore experienced noticeably hazy conditions. Levels of PM2.5, a type of pollutant, were elevated, and the Pollutant Standards Index—a measure of air quality here—reached 77, in the moderate range. The poor air quality was primarily due to unusual atmospheric conditions rather than transboundary pollution, which Singapore has faced in the past from peatland or forest fires in nearby regions.

Using the latest technology developed by my team at Nanyang Technological University (NTU), we detected calm winds in Singapore's lower atmosphere during those days—weather conditions that are unfavorable for dispersing air pollutants.

The technology is known as the 3-Dimensional Real-time Atmospheric Monitoring System (3DREAMS@SG), which comprises three advanced monitoring stations equipped with sophisticated light detection and ranging (Lidar) systems. The Lidar system is able to measure wind patterns and aerosol concentrations up to 12km vertically.

Focusing on the data from 3km above ground, we can analyze detailed, second-by-second data on air particle movements and their potential sources, including urban emissions, haze, or volcanic particulates.