Rain brings temporary relief from haze, but expert warns that pollutant-laden moisture may also pose health risks

Rainfall across Singapore on 21 September brought temporary relief from the haze, lowering air pollution levels in several areas. However, NIE climate change researcher Dr Wang Jingyu cautioned that rain may not remove all health risks associated with fine particulate pollution.

According to the National Environment Agency, the 24-hour Pollutant Standards Index fell from between 68 and 86 at 10am to between 65 and 80 by 9pm. One-hour PM2.5 concentrations also declined following afternoon showers.

PM2.5 refers to airborne particles measuring no more than 2.5 micrometres in diameter. These particles are small enough to enter the lungs when inhaled, and prolonged exposure may lead to serious health problems.

Speaking to Lianhe Zaobao, Dr Wang explained that rainfall can help to clean the air by capturing suspended pollutant particles as raindrops pass through the atmosphere. The effectiveness of this process depends on the intensity of the rain. The afternoon showers therefore helped reduce fine-particle concentrations in some parts of Singapore.

However, Dr Wang noted that under warm and humid conditions, rainwater may evaporate and the resulting moisture can combine with remaining PM2.5 particles. This can form tiny droplets that remain suspended near ground level, creating a mist-like appearance.

These droplets may be several times larger than the original PM2.5 particles and can still affect health. Larger droplets may irritate the upper respiratory tract and cause symptoms resembling those of a cold, while smaller droplets can continue to penetrate the lungs.

The respite from the haze may also be temporary. Hot spots in Kalimantan and southern Sumatra were continuing to produce moderate to dense smoke plumes, while dry conditions were expected to persist in parts of the region. With prevailing winds forecast to continue blowing from the south-east, the risk of haze affecting Singapore remained.

Dr Wang’s comments highlight that clearer skies after rainfall do not necessarily mean that all airborne pollutants have disappeared. During periods of haze, members of the public should continue to monitor official air-quality advisories and take appropriate health precautions, particularly if they are more vulnerable to respiratory irritation.

Read the original article here.