As the EPD just released the 2016 Air Pollutant Emission Inventory Report, we received interesting enquiries about this Emission report and the Concentration report released at Jan 2018.

If you care about health of yourself and your loved ones, there are 3 things you should know about the differences between Emission and Concentration:

  1. The Bigger Picture

If we need to minimize public health risk due to air pollution, controlling human exposure to air pollution is the key. Human exposure level depends on 3 factors – magnitude (concentration of pollutants), duration (time period of exposure) and frequency (occurrence of exposure).

The purpose of 2016 Emission Inventory Report (see below for what it is) is to show the quantity and trend of local emission from major sources. It focuses on the ambient level of pollution and serves as background. The report is not able to give an account of the level and trend of concentration, which largely varies from place to place due to geographical factors, and so it is difficult to judge whether the air we breathe is better or not (more or less risky to public health).

CAN analysed the concentration of major pollutants in Jan 2018. The finding was worrying – after 3 years of decline, concentration of roadside air pollution (NO2 and PM) increased by 3-5% in 2017 compared to 2016.

Analysis: ageing vehicles and ever more vehicles on the road are the causes of rising concentration of roadside pollution. Traffic jam increases both the concentration and the duration of human exposure (both passengers-in car and pedestrians are exposed to air pollution).

CAN’s advice:

There are limitations of EPD’s end-of-pipe solutions – it controls emission only. It relies on Transport Authority’s transport management solutions and bold measures to control the growth of vehicular fleet to further reduce concentration and duration of human exposure.

  1. Definitions of key terms 

When speaking of public health, it is important for everyone to understand these key concepts

i) Emission – the quantity of air pollutants emitted by various sources.

ii) Concentration – concentration of a specific air pollutant is the amount of material per unit volume of air.

iii) Exposure – it is the pollutant concentration in the air at the point of contact between the body and the external environment.

iv) Dose – it is the amount of the pollutant that actually crosses one of the body’s boundaries and reaches the body issues.


  1. What is the 2016 Emission Inventory Report? 

The inventory shows estimates of emission from 7 source categories for 6 major air pollutants in 2016.

These figures are estimated based on emission estimation models or emission compilation methodologies. Each year, the value of each parameter of different models are collected and inputted.

For example, for road transport, EPD measures emission from road vehicles by means of remote sensing equipment. By inputting value of different parameters, such as VKT (vehicle kilometer travelled), the quantity of emission is estimated.

More Readings: Response to 2016 Air Pollution Emission Inventory

Story posted on
26th Apr, 2018


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