Condensable Particulate Matter (CPM) Determination Methods: Principles, Standards, Procedures and Ap

Condensable particulate matter (CPM) determination methods quantify the vapor-phase substances in stack gas that condense into liquid or solid particles immediately after discharge into the ambient atmosphere. Because CPM can account for a substantial share of total particulate emissions from modern low-dust sources, accurate measurement in accordance with recognized standards such as U.S. EPA Method 202 and GB/T 39193-2020 has become essential for ultra-low emission compliance, air pollution control engineering and environmental impact assessment. This article explains the technical principles, sampling trains, analytical workflows, testing items and typical industrial applications of CPM determination.

Technical Overview

Condensable particulate matter (CPM) is defined as material that exists in the vapor phase at stack exit temperature but condenses and/or reacts upon cooling and dilution in the ambient air to form liquid or solid particulate matter. In contrast, filterable particulate matter (FPM) is the fraction that is captured on a heated filter at the sampling point. Total particulate matter (TPM) is the sum of FPM and CPM.

Conventional gravimetric stack testing based on ISO 9096 or U.S. EPA Method 5 measures only FPM, because the in-stack or heated filter allows vapors to pass through. As fabric filters, wet flue gas desulfurization (WFGD) systems and wet electrostatic precipitators (WESP) drive FPM to very low concentrations, CPM increasingly dominates TPM. In many coal-fired, gas-fired and waste-to-energy plants, CPM represents more than 50 percent of TPM. CPM is also a direct precursor of secondary PM2.5 formation in the atmosphere, which makes it a key focus of ultra-low emission (ULE) programs and refined air quality management.

Chemically, CPM consists of an inorganic fraction, mainly sulfates, nitrates, chlorides, fluorides, ammonium salts and trace metals, and an organic fraction comprising volatile and semi-volatile organic compounds such as alkanes, esters, phthalates and polycyclic aromatic hydrocarbons (PAHs). Determination is therefore performed by condensing these vapors in a chilled sampling train and quantifying the recovered condensate gravimetrically, often supplemented by component speciation analysis.

Testing Samples

CPM determination is applicable to flue gas and exhaust streams sampled isokinetically from stacks and ducts of stationary emission sources, including the following representative sample types:

Coal-Fired and Gas-Fired Boiler Flue Gas

Flue gas from utility and industrial boilers downstream of air pollution control devices, where low FPM concentrations make the condensable fraction a decisive contributor to total particulate emissions.

Iron and Steel Process Emissions

Stack gas from sintering machines, coke ovens, blast furnaces, basic oxygen furnaces and pelletizing plants, characterized by elevated sulfur oxides, chlorides and semi-volatile organics.

Municipal and Hazardous Waste Incineration Flue Gas

Exhaust from waste-to-energy facilities and hazardous waste incinerators, in which acid gases, heavy metals and organic pollutants form a chemically complex condensable fraction.

Cement, Glass and Building Material Kilns

Process exhaust from rotary kilns, glass furnaces and brick production lines containing alkaline salts, sulfates and trace metals in the vapor phase.

Chemical and Petrochemical Exhaust Streams

Vent gas from refining, chemical synthesis and drying units, where organic vapors constitute a large proportion of the condensable particulate load.

Testing Items

A complete CPM test campaign typically covers the following measurable parameters:

• CPM mass concentration, reported in mg/m³ on a dry basis and converted to a specified reference oxygen concentration
• Organic CPM fraction and inorganic CPM fraction, determined separately from organic solvent and aqueous recoveries
• Water-soluble ions in the condensate, including sulfate, nitrate, chloride, fluoride and ammonium, determined by ion chromatography
• Elemental composition, including Na, K, Ca, Mg, Al, Fe and heavy metals, determined by ICP-OES or ICP-MS
• Organic species such as n-alkanes, PAHs, esters and phthalates, determined by GC-MS
• Filterable particulate matter (FPM) and total particulate matter (TPM) obtained through combined sampling for mass balance and regulatory comparison

Testing Methods

Two internationally recognized method families dominate CPM determination, both built on the principle of isokinetic sampling through a heated filter followed by controlled condensation of the vapors.

U.S. EPA Method 202 — Dry Impinger Method

The sampling train consists of a Type S pitot tube, a heated probe, a filter maintained at 120 °C ± 14 °C (or an in-stack filter at stack temperature), a water-cooled condenser, a pair of impingers immersed in an ice bath, a drying column and a calibrated dry gas meter. The filter retains FPM while vapors pass into the condensation section, where CPM deposits on cooled surfaces and in the impinger water. After sampling, the train is purged with dry nitrogen at approximately 14 L/min for at least one hour to strip dissolved sulfur dioxide and prevent a positive sulfate artifact. The condenser and impingers are then recovered with deionized water for the inorganic fraction and hexane for the organic fraction. Each fraction is evaporated to dryness, desiccated and weighed on an analytical balance; the sum of the two residues yields CPM. A minimum sampled volume of about 0.85 dry standard cubic meters is recommended. When combined with EPA Method 5 or 17 in a single train, FPM and CPM are obtained simultaneously.

GB/T 39193-2020 — Condensation and Adsorption Method

This Chinese national standard specifies the determination of condensable particulate matter in flue gas from stationary sources using a condensation and adsorption configuration. Stack gas is drawn through a filter heated to stack temperature (or to approximately 120 °C where specified) into a low-temperature condenser and absorption impingers, where vapors are condensed and captured. The recovered liquid and rinses are evaporated and the residue is determined gravimetrically as CPM. The method is widely applied in ultra-low emission evaluations and can be operated in parallel with GB/T 16157 filterable dust sampling to derive TPM.

Supporting Standards

• ISO 9096, for the manual gravimetric determination of filterable particulate concentration and mass flow rate
• ASTM D6331, for gravimetric determination of particulate matter at low concentrations from stationary sources
• U.S. EPA Methods 1 through 4, for flow velocity determination, stack gas moisture and molecular weight determination used to establish isokinetic sampling conditions

Typical Sampling and Analytical Workflow

• Preliminary survey of stack geometry, gas velocity, temperature, moisture and oxygen/carbon dioxide content to set isokinetic sampling parameters
• Leak check of the train, followed by isokinetic sampling through the heated filter, condenser and impinger assembly for the required gas volume
• Nitrogen purge of the impinger section (EPA Method 202) to remove dissolved sulfur dioxide and suppress sulfate artifacts
• Quantitative recovery of the aqueous and organic fractions from the condenser, connectors and impingers
• Evaporation to dryness, desiccation and gravimetric weighing under constant-weight criteria, typically within 0.5 mg between consecutive weighings
• Optional speciation of the condensate by ion chromatography, ICP-OES/ICP-MS and GC-MS to characterize inorganic and organic components
• Data reduction to dry standard conditions, oxygen-reference conversion and comparison with applicable emission limits

Quality assurance measures include field blanks, paired duplicate trains, calibrated metering systems, temperature control of heated components and documented chain-of-custody, all of which are routinely implemented by accredited third-party laboratories.

Applications

CPM determination supports regulatory, engineering and scientific objectives across emission-intensive industries:

• Ultra-low emission compliance verification for coal-fired power plants, where particulate limits of 10 mg/m³ or lower require full accounting of both filterable and condensable fractions
• Performance evaluation and acceptance testing of upgraded air pollution control trains, including wet electrostatic precipitators, scrubber modifications and condensation heat recovery units
• Waste incineration and steel industry emission assessments, where condensable components strongly influence total particulate loading
• Development of emission inventories and environmental impact assessments requiring complete TPM data
• Research into secondary PM2.5 formation mechanisms and atmospheric chemistry studies
• Comparative studies of fuel switching, co-firing and flue gas conditioning strategies aimed at reducing condensable emissions

FAQ

What is the difference between condensable and filterable particulate matter?

Filterable particulate matter is captured on a filter at stack temperature during sampling, whereas condensable particulate matter exists as vapor at stack temperature and only forms liquid or solid particles after the gas cools in the atmosphere or in the chilled section of the sampling train. Total particulate matter equals the sum of both fractions.

Why is the nitrogen purge necessary in EPA Method 202?

Sulfur dioxide in the flue gas dissolves in the impinger water and can oxidize to sulfate during recovery, creating a positive bias that would be falsely reported as inorganic CPM. Purging the impinger train with dry nitrogen after sampling removes dissolved sulfur dioxide before sample recovery, significantly improving result accuracy.

At what temperature is the filter maintained?

The filter is typically held at 120 °C ± 14 °C for heated out-of-stack configurations, or at stack temperature for in-stack arrangements. This temperature is high enough to prevent premature condensation on the filter while allowing condensable vapors to pass through to the condensation section.

Is CPM considered to be PM2.5?

CPM generally condenses into particles with aerodynamic diameters of 2.5 micrometers or less after discharge, so it functionally contributes to ambient PM2.5. However, regulatory stack testing distinguishes CPM from filterable PM2.5 measured with cyclone-based methods such as EPA Method 201A, and the two are reported separately unless a regulation explicitly requires their sum.

Which method should be selected for a project?

The choice depends on the governing regulatory framework. Projects under Chinese ultra-low emission programs commonly apply GB/T 39193-2020, while international projects and baseline studies frequently adopt EPA Method 202. Both methods share the same fundamental principle, and accredited third-party laboratories can execute either standard with paired FPM sampling to deliver complete TPM data.

What are the main quality control requirements?

Essential quality control includes pre- and post-sampling leak checks, field blanks, duplicate sampling trains, calibration of the metering system against a reference gas meter, strict temperature control of heated and chilled sections, constant-weight weighing criteria for residues, and full documentation of sample recovery and analysis.