The haze and health: a blog about the fog.

The haze is an atmospheric phenomenon where pollutant particles accumulate in the air and obscure the normal clarity of the sky. In Singapore, this usually happens when the prevailing southwest monsoon winds blow the smoke from regional forest fires to Singapore. This phenomenon is not new and has been occurring regularly since 1994. In 1997, it featured on the front page of the Straits Times and news was made again in early October this year when the pollutants standard index or PSI hit 150 (>100 being labelled as unhealthy) for a 24-hour period, this being the worst since 1997 when the index reached 138. Singapore’s blue skies begin to clear up again with the start of the inter-monsoon rains in late October, bringing PSI readings to lower levels again, before these readings fade into oblivion again, at least until next year. The PSI actually measures the main gaseous (NO2, CO, SO2 and O3) and particulate matter pollutants in our environment. Of these 5 types of pollutants that are measured, the reading of the predominant pollutant present is the one reported. During the haze, the predominant pollutant is PM10 or airborne particulate matter less than 10 microns in diameter, which is roughly about a sixth of the diameter of human hair. Though not without precedence, the infamous London Fog of 1952 has clearly demonstrated that air pollution can kill, with large short-term and long-term increases in mortality and cardiopulmonary disease. The US and European time series have consistently shown short-term associations between temporal day-to-day variations in PM10 exposure and rate of death from all causes and cardiopulmonary illnesses.1,2 There has indeed been a heightened interest in the effects of air pollution after two prospective cohort studies suggested that exposure to PM10 pollution is associated with increased rates of mortality. The landmark study by Dockery et al3 followed 8111 subjects over a 15-year period in 6 US cities, while the American Cancer society followed 522,138 adults from 1982 to 1989.4 When follow-up time was doubled to more than 16 years for the American Cancer Society study, Pope et al5 concluded that long-term exposure to combustionrelated fine particulate air pollution is an important environmental risk factor not only for cardiopulmonary but