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Air and Coastal Water Quality Monitoring

Real-time Monitoring of Criteria Air Pollutants

The ambient air quality in Singapore is continuously monitored through a network of air monitoring sensors across Singapore. These sensors measure the level of the six criteria air pollutants; namely, sulphur dioxide (SO2), nitrogen dioxide (NO2), ozone (O3), carbon monoxide (CO) and particulate matter (both PM10 and PM2.5, with diameters of less than 10 and 2.5 micrometres, respectively). 

For ambient air quality monitoring, the concentrations of these criteria air pollutants are used to compute the Pollutant Standards Index (PSI)  over a rolling 24-hour period.  These PSI readings are reported on an hourly basis on the NEA website, haze microsite and myENV app. The readings are broken down by the north, east, south, west and central regions of Singapore as measured at NEA’s five national reporting stations located in these regions.

Read more on PSI and the 6 criteria pollutants.


Real-time Monitoring of Ambient Volatile Organic Compounds (VOCs)

Volatile Organic Compounds (VOCs) are organic chemical vapours which can come from both man-made and natural sources. These compounds can cause smells by themselves or when they react with other VOCs. They are often involved in complex atmospheric photochemical reactions that contribute to ground-level ozone formation. Ozone is one of the 6 key air pollutants monitored by NEA.  

Apart from the 6 criteria pollutants, NEA also continuously monitors VOCs as additional parameters at our monitoring stations, including at four stations located in the north-eastern region of Singapore. The VOCs monitored include Benzene, Toluene, Xylene (BTX), which are industrial emissions that are also monitored by other environmental agencies such as the United States Environmental Protection Agency.  

In addition, NEA officers are equipped with portable instruments and detectors to carry out on-site measurements, and collect air samples at selected locations for laboratory analysis for a further spectrum of chemical compounds. 

Read more on  VOCs and  Ozone.

One of the VOCs of interest is benzene. The World Health Organization (WHO) provides risk-based guidelines for long-term benzene exposure, but does not set a single threshold. Jurisdictions such as the European Union (EU) have established an annual limit value of ~1.6 parts per billion (ppb) for ambient benzene concentrations. Singapore’s national ambient benzene level is  well below this international benchmark.

For shorter term exposure, the US Environmental Protection Agency (EPA) has established a set of Acute Exposure Guideline Levels (AEGL), which describes the airborne concentration of a chemical above which harmful effects could occur for the general population. There are three AEGL tiers, each defined for specific exposure durations. For instance, the 1-hour AEGL-1 level, which is the least severe of the three AEGL tiers, represents the airborne concentration of chemicals above which the general population could experience notable discomfort or irritation. The hourly benzene readings across the ambient air monitoring stations in residential areas are well below 1% of the AEGL-1 threshold for benzene.

Find out more about benzene trends at monitoring stations across Singapore.


 


Real-time Monitoring of Coastal Water Quality

NEA has a network of eight buoy-based water quality monitoring stations along the Straits of Johor and the Straits of Singapore to measure the key physical, chemical and microbiological water quality parameters.  

Real-time data from these stations are continuously transmitted to an operational management system that manages and processes the data to assess if the water quality has been affected by oil spills, eutrophication of seawater, and algae blooms that may affect our fish farms located at our coastal waters. 

In addition, as may be required by the situation, NEA also takes grab samples to analyse additional water quality parameters, such as heavy metals and VOCs.


Routine Coastal Water Monitoring Programme 

NEA regularly monitors the water quality of coastal areas. Coastal water samples are analysed for metals, total organic carbon, and other physical, chemical and bacteriological parameters. Apart from monitoring for recreational purposes, e.g. use of recreational beaches, data collected from coastal water monitoring is also shared with agencies such as SFA as part of the on-going efforts to monitor the levels of planktons in the sea, which have implications on the Singapore’s coastal fish farms.  

Read more on why NEA monitors water quality of coastal areas.



Common Q&As

1. Why does NEA monitor PSI and the six key air pollutants? 

Good air quality safeguards public health. NEA tracks the ambient level of six key air pollutants; namely, particulate matter (PM2.5 and PM10), sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO) and ozone (O3). NEA benchmarks Singapore’s air quality against the World Health Organisation Air Quality Guidelines (WHO AQG), while keeping a watching brief on the United States Environmental Protection Agency (US EPA) National Ambient Air Quality Standards and the air quality in major cities. 

The Pollutant Standards Index (PSI) is an index to provide accurate, timely and easily understandable information about daily levels of air quality. The PSI over a rolling 24-hour period measured at the five national reporting stations, are reported on an hourly basis on the NEA website, haze microsite and the myENV app. Other than the PSI, the 1-hour PM2.5 concentrations are also made available to the public as additional information on air quality. 

 
2. Where do Volatile Organic Compounds (VOCs) come from?

It is not uncommon to have VOCs in the environment. This is because VOCs are emitted from biogenic sources, mainly trees, as well as a variety of anthropogenic sources such as motor vehicles, chemical manufacturing facilities, refineries, factories, as well as consumer and commercial products. 

VOCs are also released from burning fuels, such as gasoline, wood, coal, or natural gas. They are present in smaller traces in common household products like paint, varnishes, wood preservatives, moth repellents, air fresheners, hobby supplies, aerosol sprays, fluid solvents, automotive products, glue and cleaning products.

 
3. What is ground-level ozone? 

Ground-level ozone is ozone that is not emitted directly into the air from ozone sources, but is produced in reactions between oxides of nitrogen (NOx) and VOCs. This happens when pollutants emitted by vehicles and industries undergo complex chemical reactions in the presence of sunlight. Hot sunny days in an urban environment tend to result in higher ozone levels. As excessive ozone in the air can be harmful to health, increasing the impairment of respiratory functions, it is one of the key air pollutants monitored in Singapore, as well as in other countries. 

 
4. Why does NEA monitor the water quality of coastal areas?


NEA regularly monitors the water quality of coastal areas. Coastal water samples are analysed for key physical, chemical, microbiological and bacteriological parameters for long term trend analysis, and closely monitored for changes in water quality due to oil or chemical spills, fish kills, eutrophication of seawater and algae blooms that could potentially affect our fish farms and marine biodiversity. 

The water quality of seven popular recreational beaches is also monitored on a weekly basis to assess the suitability of the beaches for primary water contact activities like swimming, skiing and wakeboarding. The water quality is assessed based on the WHO guidelines of enterococcus counts not exceeding 200 counts per 100ml for 95 per cent of the time.


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