Stack Monitoring, Ambient Monitoring and Environmental Evidence
Stack monitoring tells us what leaves a source. Ambient monitoring tells us what is present in the surrounding environment. Neither, on its own, establishes the complete causal pathway between a facility and population exposure.
- Reviewed
Environmental monitoring is strongest when the question determines the measurement.
Different monitoring systems answer different questions.
Stack monitoring
Stack testing and continuous emissions monitoring examine the source.
They can provide evidence concerning pollutant concentration, mass release, operating conditions, control-system performance and compliance.
This establishes what leaves the facility.
Ambient monitoring
Ambient monitors measure the surrounding environment.
They may measure particulate matter, gases, metals and other pollutants at defined receptor locations.
This can provide direct evidence about environmental concentrations where people or ecosystems may be exposed.
The attribution problem
Ambient pollution can originate from many sources.
A measured concentration may include contributions from transport, industry, heating, shipping, agriculture, fires and long-range transport.
Detection near a facility therefore does not automatically establish that facility as the sole or dominant source.
Connecting source and receptor
Linking stack emissions to ambient concentration may require emissions inventories, meteorology, dispersion modelling, source signatures, temporal patterns and spatial analysis.
This is the causal bridge between the source and receptor.
Deposition
Neither ordinary stack nor ambient-air monitoring necessarily describes contamination accumulated on soil, vegetation or water.
Additional environmental sampling may therefore be necessary.
Human exposure
Ambient concentration still does not automatically equal individual dose.
People move.
They spend time indoors, outdoors, at work and travelling.
Exposure assessment may therefore require additional information.
Monitoring system
A robust evidence architecture may include source monitoring, ambient monitoring, deposition measurement, environmental sampling, dispersion analysis and exposure assessment where appropriate.
Governing principle
Source evidence and receptor evidence are complementary.
The strongest environmental conclusion usually comes from understanding how they connect, rather than asking one monitoring system to answer every question.
Selected sources and scope
Sources support the indicated concepts or dated assessments; they do not endorse GCCEI or validate a particular installation. Checked on 18 October 2026.
- R06 · US EPA: Continuous Emission Monitoring Systems. Web resource, accessed 18 October 2026. Monitoring-system functions, calibration and quality assurance; not any facility result.
- R05 · US EPA: Air Quality Dispersion Modeling. Page updated 31 October 2025. Emissions, meteorology, dispersion and modelled receptor concentrations.
- R01 · US EPA: About Risk Assessment. Page updated 20 May 2026. Hazard, exposure, risk, uncertainty and health-protective assumptions.