SINGAPORE – The haze has returned to Singapore today (Aug 20), according to TODAY readers reporting on the worsening air quality in many areas of Singapore. The National Environment Agency’s three-hour Pollutant Standards Index (PSI) had risen to 34 at 10am, up from 25 at 6am. The reading is an average of the PSI over the previous three hours. A PSI reading of 34 falls within the "good" zone. Reports of the haze seemed to be concentrated in the west, where reader @eugene_kee tweeted "#sghaze seen at pasir panjang. Maybe on the way?" Reader @LividEye corroborated the report, tweeting "We are in Clementi Pasir Panjang, South West area. And yes, the #sghaze seemed to be looming in the skies right now." In the east, reader @endorphynn wrote that the situation in the Marine Parade area was "bad. Hazy.. Definitely smell it in e air", while @sharon_pow said that the situation in Eunos and Paya Lebar was "ok". The NEA has said that it is currently investigating, and will provide an update later this afternoon. The three-hour PSI hit a record high of 401 at 12pm on June 21, in a third straight day of records, although two days of mostly clear skies followed over the next few days. The three-hour PSI readings are calculated based on PM10 concentrations only. The PSI index was developed by the United States’ Environmental Protection Agency (EPA) to provide accurate and timely information about daily levels of air pollution. Air pollutants such as sulphur dioxide, nitrogen dioxide, ozone, carbon monoxide and particulate matter called PM10 (particulate matter of 10 microns or smaller in size) are used in the determination of the index. The 24-hour PSI reading at 11am was 23-29, in the 'good' range. For the PM2.5 concentration, the 24-hour reading at 11am was 13-17 μg/m3. The PM2.5 reading measures fine particles measuring 2.5 micrometres or less in diameter, as well as ultrafine particles, and soot. The Ministry of Health has set up a 24-hour hotline to help with public queries on the haze: 1800-333-9999 PSI Air quality descriptor 0-50: Good 51-100: Moderate 101-200: Unhealthy 201-300: Very unhealthy +300: Hazardous Source: http://tdy.sg/neapsi More about the PSI: http://tdy.sg/PSIhowandwhy