24-hour PSI returns to moderate range in northern, southern Singapore; 1-hour PM2.5 elevated in 3 regions

Air quality in Singapore has improved, with 24-hour Pollutant Standards Index (PSI) readings in the northern and southern regions returning to the moderate range on Tuesday (Sept 15) afternoon.

Northern Singapore recorded unhealthy air quality for 10 hours, from 1am on Tuesday, before returning to the moderate range at 10am. The southern region spent 14 hours in the unhealthy range before improving to moderate levels at 11am.

At 3pm, data from the National Environment Agency (NEA) showed that PSI readings ranged from 92 to 135, placing air quality in the moderate to unhealthy bands. Central Singapore recorded the highest PSI reading at 135, followed by the western (118) and eastern (115) regions.

Meanwhile, the one-hour PM2.5 reading, an indicator of fine particulate matter in the air and a measure of current air quality, ranged from 48 to 101 at 3pm.

A reading of between 0 and 55 µg/m3 falls within the normal band, while readings ranging from 56 to 150 are classified as within the elevated band.

All three regions with moderate air quality — central (101), western (71) and eastern (70) Singapore — also recorded elevated PM2.5 readings.

NEA's historical data also shows that while PM2.5 concentration readings in the three regions fell back into the normal band on Tuesday morning, they began rising again from around 1pm.

Why PM2.5 is the number to watch

While scientific and epidemiological studies on the health effects of exposure to particulate matter have shown that the impact of short-term exposure is low, NEA provides hourly 1-hour PM2.5 readings.

These readings provide a real-time indication of the concentration of fine particles that can enter the lungs and bloodstream.

However, raw PM2.5 figures do not necessarily tell the average person what precautions to take. As such, NEA groups PM2.5 readings into four bands: normal (0-55 µg/m3), elevated (56 to 150), high (151 to 250), and very high (251 and above).

It also "translates" what this means into an outdoor activities planning guide for healthy and vulnerable groups planning to conduct or participate in such activities immediately.

Members of the public should note that the health impact of haze is dependent on one's health status, the PSI level, and the length and intensity of outdoor activity.

They may refer to the following guide when planning to take part in outdoor activities immediately:

新加坡的空气质量有所改善，周二（9月15日）下午，北部和南部地区的24小时污染物标准指数（PSI）读数已恢复到中等水平。

新加坡北部地区周二凌晨1点起连续10小时空气质量不健康，之后于上午10点恢复至中等水平。南部地区则连续14小时处于不健康水平，之后于上午11点改善至中等水平。

下午3点，国家环境局（NEA）的数据显示，空气污染指数（PSI）读数在92至135之间，空气质量处于中等至不健康水平。新加坡中部地区的PSI读数最高，为135，其次是西部地区（118）和东部地区（115）。

与此同时，下午 3 点，PM2.5 一小时读数（空气中细颗粒物的指标，也是衡量当前空气质量的指标）在 48 到 101 之间。

读数在 0 到 55 µg/m3 之间属于正常范围，而读数在 56 到 150 之间则属于升高范围。

新加坡中部（101）、西部（71）和东部（70）这三个空气质量中等的地区，PM2.5 读数也均偏高。

国家环境局的历史数据显示，虽然周二上午这三个地区的 PM2.5 浓度读数回落到正常范围内，但从下午 1 点左右开始又开始上升。

为什么PM2.5是值得关注的指标

虽然有关接触颗粒物对健康影响的科学和流行病学研究表明，短期接触的影响较小，但新加坡国家环境局 (NEA) 仍提供每小时 1 小时的 PM2.5 读数。

这些读数可以实时指示可能进入肺部和血液的细颗粒物的浓度。

然而，PM2.5的原始数值并不一定能告诉普通人应该采取哪些预防措施。因此，新加坡国家环境局（NEA）将PM2.5读数分为四个等级：正常（0-55微克/立方米）、偏高（56至150微克/立方米）、高（151至250微克/立方米）和极高（251微克/立方米及以上）。

它还“转化”了这一含义，为计划立即开展或参与此类活动的健康和弱势群体提供户外活动规划指南。

公众应注意，雾霾对健康的影响取决于个人的健康状况、PSI 值以及户外活动的持续时间和强度。

他们计划立即参加户外活动时，可以参考以下指南：