Condensable Particulate Matter (CPM) Emission Testing: Methods, Standards, and Applications

Condensable particulate matter (CPM) emission testing measures the portion of stack emissions that exists as vapor at flue-gas temperature but condenses into liquid or solid particles immediately after release into the atmosphere. Following established procedures such as EPA Method 202 and China's HJ 1263-2022, this test is increasingly required for ultra-low emission verification, emission inventory development, and secondary PM2.5 control at stationary sources. Accredited third-party laboratories perform the sampling and gravimetric analysis to quantify total, inorganic, and organic CPM fractions in mg/Nm³.

Technical Overview

Condensable particulate matter (CPM) is defined as material that is in the vapor phase at stack temperature but condenses and/or reacts upon dilution and cooling in the ambient air to form solid or liquid particulate matter after passing through a filter heated to stack conditions. Because a conventional particulate test train captures only filterable particulate matter (FPM), CPM is invisible to standard compliance methods yet can constitute a substantial share of true total primary particulate emissions.

Total particulate matter emitted by a stationary source is therefore expressed as:

• Total PM = Filterable PM (FPM) + Condensable PM (CPM)
• FPM is captured on a heated or in-stack filter (e.g., EPA Method 5, Method 201A, ISO 9096)
• CPM is collected downstream of the filter in a condenser and cold impinger train (EPA Method 202, HJ 1263-2022)

The technical significance of CPM has grown sharply with ultra-low emission programs. At facilities equipped with high-efficiency controls such as wet flue gas desulfurization (WFGD) and wet electrostatic precipitators (WESP), filterable PM concentrations can be driven below 5 mg/Nm³, while CPM frequently accounts for 30–70% of total primary particulate emissions. CPM is also chemically important: its sulfate, nitrate, ammonium, and semi-volatile organic components act as precursors for secondary PM2.5 formation and regional haze, making it a key target for atmospheric environmental management.

Testing Samples

Flue Gas from Combustion Sources

Samples are extracted from flue gas ducts and stacks of coal-fired boilers, gas-fired boilers and turbines, biomass-fired units, and on-site industrial furnaces. Sampling ports, platforms, and velocity measurement points must satisfy the geometric requirements of the applicable sampling standard.

Treated Exhaust Downstream of Pollution Control Devices

The most common sampling location is the outlet of air pollution control systems—after electrostatic precipitators, baghouses, WFGD absorbers, or WESPs. Wet, saturated, low-temperature flue gas leaving scrubbers is particularly prone to high CPM content, so outlets of these devices are the focus of most evaluation campaigns.

Industrial Process Emissions

Representative process sources include iron ore sintering machines, coking ovens, cement kilns, hazardous waste and municipal solid waste incinerators, glass furnaces, and petrochemical or chemical process vents, all of which emit semi-volatile inorganic salts and organics that contribute to CPM.

Testing Items

A complete condensable particulate matter emission test typically reports the following items, expressed in mg/Nm³ (dry basis, 0 °C, 101.325 kPa, corrected to a reference oxygen concentration):

• Total condensable particulate matter (Total CPM)
• Inorganic condensable particulate matter (Inorganic CPM), determined from the aqueous condensate residue
• Organic condensable particulate matter (Organic CPM), determined from the solvent-extractable organic residue
• Filterable particulate matter (TPM, or PM10 and PM2.5 fractions) when combined sampling is performed
• Total primary particulate matter (FPM + CPM) for emission characterization
• Optional speciation: water-soluble ions (SO4²⁻, NO3⁻, Cl⁻, F⁻, NH4⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺), trace metal elements, and organic constituents by ion chromatography, ICP-OES/ICP-MS, and GC-MS

Testing Methods

EPA Method 202 — Dry Impinger Method

US EPA Method 202 is the internationally recognized reference procedure. The sample train consists of a heated probe and filter (120 ± 14 °C, or an in-stack filter when combined with Method 201A), followed by a water-saturated condenser that cools the gas to 30 °C or less, a condensable-trap impinger immersed in an ice bath, and a silica gel drying section. After each run, the train is purged with high-purity nitrogen (typically one hour at approximately 14 L/min) to strip dissolved sulfur dioxide from the collected condensate and prevent positive SO2-derived bias. The condenser and impinger are then rinsed with deionized water and extracted/rinsed with organic solvent; the aqueous fraction is evaporated to dryness and weighed to obtain the inorganic CPM mass, while the organic extract is evaporated and weighed to obtain the organic CPM mass.

Combined EPA Methods 201A/202

For simultaneous determination of filterable PM10/PM2.5 and CPM, Method 201A (constant-sampling-rate, in-stack cascade cyclone/filter) is coupled with a Method 202 back half. This combined train yields size-fractionated filterable particulate plus condensable particulate in a single integrated run, allowing direct calculation of total primary particulate emissions.

Chinese Standard HJ 1263-2022

China's ecological environment standard HJ 1263-2022 establishes the dry impinger method for determining condensable particulate matter from stationary sources. Technically aligned with EPA Method 202, it defines train configuration, condenser temperature control, nitrogen purge, sample recovery, evaporation, and gravimetric weighing procedures, and is the method of record for domestic ultra-low emission assessment projects.

Laboratory Analysis, Quality Control, and Reporting

All residues are dried to constant weight and weighed on an analytical balance readable to 0.1 mg. A rigorous quality control program is essential and typically includes:

• Field train blanks and reagent blanks to correct background contamination
• Ultra-high-purity nitrogen verification for the post-run purge
• Leak checks before and after each sampling run
• Calibrated metering systems, thermocouples, and barometric measurements for accurate sample volume conversion to standard conditions
• A minimum of three valid sampling runs per test condition, with results averaged and reported on a dry, reference-O2 basis

Applications

Condensable particulate matter emission testing supports a wide range of regulatory, engineering, and scientific objectives:

• Ultra-low emission (ULE) compliance demonstration at coal-fired power plants, steel plants, and cement plants, where CPM must be quantified to confirm true total particulate performance
• Evaluation of control technology upgrades, including WESP retrofits, low-temperature economizers, condensation scrubbers, and scrubber additives aimed at capturing CPM precursors
• Preparation of emission inventories and environmental impact assessments that require complete primary particulate characterization
• Source apportionment and secondary PM2.5 research, using CPM chemical speciation data
• Performance acceptance testing for newly constructed or modified stationary sources and permitting support
• Corporate ESG and environmental disclosure reporting of total particulate emissions

FAQ

What is the difference between filterable and condensable particulate matter?

Filterable PM is captured on a filter at stack temperature and consists of particles already in solid or liquid form in the duct. Condensable PM passes through that filter as vapor and only forms particles after the plume cools and dilutes in the atmosphere. Both fractions must be measured to obtain true total particulate emissions.

Why has CPM testing become so important in recent years?

Modern control devices reduce filterable PM to very low concentrations, so CPM now often represents the dominant share of total particulate emissions at well-controlled plants. Regulators and plant owners therefore test CPM to verify ultra-low emission performance and to address secondary PM2.5 formation.

Which standards govern CPM emission testing?

The primary methods are US EPA Method 202, combined EPA Methods 201A/202 for simultaneous FPM and CPM, and China's HJ 1263-2022 dry impinger method. EPA Methods 5 and 17 and ISO 9096 cover the filterable fraction when tested separately.

Is isokinetic sampling required for CPM?

Because CPM exists in the vapor phase at the nozzle, it is not strictly dependent on isokinetic extraction; however, combined trains used for FPM plus CPM must be operated isokinetically to validate the filterable PM result.

Why is the nitrogen purge performed?

Dissolved sulfur dioxide in the collected condensate can oxidize to sulfate during evaporation and artificially inflate the inorganic CPM result. Purging with high-purity nitrogen after sampling removes dissolved SO2 and eliminates this positive bias.

How are the results reported?

Results are reported as inorganic, organic, and total CPM in mg/Nm³, dry basis at 0 °C and 101.325 kPa, corrected to the specified reference oxygen concentration, based on the average of at least three valid runs. When combined with filterable PM data, total primary particulate emissions are also calculated.