PETALING JAYA (THE STAR/ASIA NEWS NETWORK) - Six areas have recorded unhealthy air pollutant index (API) levels on Monday.

As of 3pm, Nilai recorded a reading of 112, Seremban recorded a reading of 104, Banting recorded 116, Port Klang recorded 135, Putrajaya recorded 107, and Shah Alam recorded a reading of 101.

An API reading of between 0 and 50 is considered good, 51 to 100 (moderate), 101 to 200 (unhealthy), 201 to 300 (very unhealthy), and 301 and above (hazardous).

Shah Alam recorded a borderline unhealthy ozone level, which may lead to some chest discomfort, cough, and shortness of breath.

Seremban and Putrajaya are also two areas that recorded readings at the border of moderate and unhealthy levels.

The API is calculated based on five major air pollutants, namely Sulphur Dioxide (SO2), Nitrogen Dioxide (NO2), Ground Level Ozone (O3), Carbon Monoxide (CO) and particulate matter with a diameter below 10 micrometers (PM10).

Most of these pollutants come from various sources such as industries, motor vehicles, open burning and power generation.

The concentrations of these five pollutants are measured in 52 automatic air quality stations throughout Malaysia, mainly located in industrial and urban areas.