KUALA LUMPUR, April 5 — Air quality deteriorated across parts of the Klang Valley and Negeri Sembilan today, with four areas breaching unhealthy levels and Putrajaya emerging as the hardest hit, even as broader national data suggests conditions remain mixed.

Data from the Department of Environment’s Air Pollution Index Management System (APIMS) showed Putrajaya, Jenjarom in Selangor, and Seremban and Nilai in Negeri Sembilan all recorded Air Pollutant Index (API) readings above 100 as of 10am.

Putrajaya’s readings have been the most persistent, first crossing into unhealthy territory at 4am yesterday before hovering around the 150 mark. After a brief dip overnight, levels rebounded this morning, reaching 152 by 10am.

Nilai saw a sharp overnight spike, crossing the threshold at 11pm yesterday and climbing to 124 by 8am before easing slightly to 102 by mid-morning. 

Nearby Seremban entered the unhealthy range later, recording 119 at 7am and worsening to 130 by 10am, though it eased to 105 by early afternoon.

In Selangor, Jenjarom also breached the unhealthy level at midnight yesterday, peaking near 150 before improving marginally to 143 by 10am Sunday.

Elsewhere, conditions showed signs of recovery. Johan Setia in Klang, which had recorded unhealthy levels since early Friday and briefly exceeded 160 on Saturday morning, returned to moderate levels at 97 by 10am.

Real-time data from the World Air Quality Index project offers a broader snapshot, showing much of urban Malaysia still within the moderate range despite localised spikes. 

As of the latest readings, cities such as Kuala Lumpur, Petaling Jaya and Klang were largely registering moderate air quality levels, underscoring how conditions can vary sharply between monitoring points.

Nationwide, most monitoring stations remained within safer ranges, with 15 stations recording good air quality and 48 at moderate levels.

The API, Malaysia’s main public gauge of air quality, is derived from the highest sub-index among six pollutants — PM2.5, PM10, ozone, carbon monoxide, nitrogen dioxide and sulphur dioxide — and categorised from good to hazardous based on health risk.

No single cause has been officially confirmed, but the pattern is consistent with early signs of haze conditions along the west coast of Peninsular Malaysia.

Authorities have noted a rise in open burning incidents nationwide since mid-March, fuelled by dry weather.

Johor is among the states with the highest number of such cases, adding to concerns that haze could worsen if conditions persist.