Primer on Pollution Source Apportionment


Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment

Building an effective air pollution control plan for the cities and the regions, it is important to know the contribution of sources. This is not a easy process, as it involves many steps, some related to field experiments, some related to laboratory analysis, some related to (statistical and predictive) modeling, and some related to linking the results to pollution control planning.

CategoryBottom-up source modelling approachTop-down receptor modelling approach
basic definitionIn this approach an emissions inventory is established for all the known sectors (anthropogenic and natural) and processed through a meteorology coupled chemical transport model to ascertain their share of contribution to the select airshed.In this approach, an ambient sample is analysed for its chemical composition (in the form of ions, metals, and carbon species) and statistically matched with the chemical profiles of different fuels to ascertain their share of contribution to the measured ambient sample.
source definitionTypically, source refers to a sector and in some cases, it can refer to a region.Typically, source refers to the type of fuel and with some handwaving it can refer to a sector.
Major limitationsThe emissions inventory work is heavily dependent on the depth of activity levels, fuel consumption data, and emission factors which vary by region and combustion technology in place.It is very difficult to differentiative between the sectors burning the same fuels. For example, diesel burnt at a generator set and diesel burnt in a truck will show the same chemical profile; dust from wind erosion and dust from the side of the roads that is resuspended will have the same chemical profile; biomass burnt in an open field and biomass burnt inside the house for cooking will have the same chemical profile.
Spatial representativenessAnalysis results are representative of the entire airshed selected for the emissions and the chemical transport modelling exercise. The grid resolution can provide further details within the airshed.Analysis results are representative of an area covering 2-km radius of the sampling location. The representativeness of the overall result to a city or a region depends on the number of sampling locations and the number of samples collected in the city or the region.
Temporal representativenessAnalysis results will be available at various temporal scales – by hour, by day, by month, and by season, depending on the granularity of the emissions and the chemical transport modelling exercise.Analysis results are representative of the day and time of the sample collected. Because of this, multiple samples are required by month and season to ascertain the temporal trends in source contributions.
Financial burdenVARIABLE - depending on the granularity of the emissions and chemical transport modelling exercise; primary data collecting activities; and modelling tools employed.HIGH - depending on the number of sampling locations in the airshed and number of samples collected per season.
Laboratory needsHIGH - when primary data collection is carried out to ascertain the emission factors by fuel and by sector.HIGH - a stringent set of protocols must be followed starting from sampling, storage, chemical analysis, source profiling, QAQC, and receptor modelling.
Personnel needsLOW to MEDIUM - when the emission inventories are available and the chemical transport model setup is operational, personnel needs can be low.HIGH - Includes personnel to perform field, laboratory and statistical modeling tasks as described below. Advanced, semi-autonomous samplers can reduce personnel time in the field.
Personnel skill needsHIGH - experienced staff is required to collate/manage/map/analyse the emissions inventory for the airshed; experienced staff is required to operate/calibrate/analyse the meteorology coupled chemical transport models for the airshed to ascertain the source contributionsHIGH - experienced staff is required to collect/store/record the samples during the field experiment; experienced staff is required to operate/calibrate/analyse the samples in the lab; and experienced staff is required to conduct the receptor modelling exercise involving selection and use of relevant source profiles.
Computational needsHIGH - depending on the chemical transport model of choice, chemical mechanism selected, spatial and temporal resolution of the modelling system, and range of output parameters, computational needs can range from HIGH to VERY HIGHMINIMUM - only part when computational facilities are required is the receptor modelling exercise, which is a statistical package capable of running on a laptop
Study time scalesTypically, less than one year.Typically, one year for the sample exercises and 1-2 years for chemical analysis and receptor modelling (which entirely depends on the capacity of the lab)

We structured these steps into a primer explaining the process of source apportionment using these 2 methods to support an informed air quality management plan. You can download a pdf version of the primer here or browse the pages below.

Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment
Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment
Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment
Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment Primer on Source Apportionment
  • Tools for improving air quality management: A review of top-down source apportionment techniques and their application in developing countries. Publication by the World Bank (2011) [PDF]
  • An 101 overview of “air pollution monitoring
  • A version of the (above) table was published in Accelerating city progress on clean air: Innovation and action guide – Technical report with Vital Strategies (New York, USA, 2020) Download