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SINGAPORE \u2013 Air quality deteriorated over Singapore on Sept 15<\/span><\/a>, with the Pollutant Standards Index (PSI) reaching<\/span><\/a> unhealthy levels<\/span><\/a> in all parts of the country in the early hours of the morning before improving slightly.<\/p>\n Previously, bouts of unhealthy haze were detected only in certain parts of the country.<\/p>\n The PSI, a measure of air quality here, registered readings of between 104 and 154 at 6am on Sept 15, before dropping slightly to between 92 and 131 at 6pm.<\/p>\n Air quality is considered moderate when PSI levels are between 51 and 100, and unhealthy when PSI readings are above 100.<\/p>\n At that level, healthy people should reduce prolonged or strenuous outdoor activities, while those with chronic heart and lung disease should avoid such activities.<\/p>\n Unhealthy levels of haze were first detected in central Singapore on Sept 4. Since then, hazy conditions have prevailed across Singapore.<\/p>\n The PSI on Sept 16 is expected to be between the high-moderate to mid-unhealthy range, said the National Environment Agency.<\/p>\n Some organisations have implemented measures to protect people against the haze.<\/p>\n