Condensable Particulate Matter (CPM) Mass Concentration Testing: Methods, Standards, and Application

Condensable particulate matter (CPM) mass concentration testing quantifies the vapor-phase substances in stack gas that condense into liquid or solid particles after discharge into the atmosphere, a fraction that conventional filterable PM monitoring cannot capture. Using reference methods such as US EPA Method 202 and China's HJ 1077-2019, accredited third-party laboratories deliver accurate CPM measurement for ultra-low emission evaluation, permitting, and secondary PM2.5 research. This article explains the technical principles, sampling and analytical procedures, applicable industries, and frequently asked questions related to CPM detection.

Technical Overview

Condensable particulate matter (CPM) refers to substances that exist in the vapor phase in flue gas at stack temperature but condense into liquid or solid particulate form immediately after the gas is discharged into the ambient atmosphere. Unlike filterable particulate matter (FPM), which is retained on a heated filter during sampling, CPM passes through the filter and can only be captured after the sample stream is cooled. Total particulate matter (TPM) emitted by a stationary source is therefore the sum of the filterable and condensable fractions (TPM = FPM + CPM).

CPM is composed of inorganic constituents—such as sulfur trioxide/sulfuric acid mist, sulfates, nitrates, chlorides, ammonium salts, and trace metals—and organic constituents, including semi-volatile organic compounds and polycyclic aromatic hydrocarbons. Once condensed, these particles are predominantly in the submicrometer range and contribute directly to ambient PM2.5 and secondary aerosol formation.

As ultra-low emission retrofitting has driven filterable PM concentrations in many facilities to below 5 mg/m³ or even 1 mg/m³, CPM has become a dominant share of residual stack particulate emissions. The principal reference methods for CPM determination are US EPA Method 202 (Appendix M to 40 CFR Part 51) and the Chinese environmental protection standard HJ 1077-2019 (dry impinger method), while the filterable fraction is sampled in parallel according to EPA Method 5, EPA Method 201A, or GB/T 16157.

Testing Samples

CPM testing is performed on flue gas sampled directly from the stacks or ducts of stationary emission sources. Typical sample sources include:

Coal-Fired and Gas-Fired Power Plants

Utility and industrial boilers equipped with SCR, ESP or fabric filters, wet flue gas desulfurization (WFGD), and wet electrostatic precipitators (WESP), where CPM may account for the majority of residual particulate emissions.

Municipal and Hazardous Waste Incineration Plants

Combustion outlets and flue gas cleaning system stacks where acidic gases, heavy metals, and organic micropollutants form significant condensable fractions.

Steel, Cement, and Building Material Industries

Sintering machines, pelletizing furnaces, rotary kilns, dryers, and related high-temperature process stacks.

Chemical, Petrochemical, and Refining Facilities

Process heaters, catalytic cracking units, acid mist scrubber outlets, and vents carrying semi-volatile organics and acid vapors.

Biomass, Sludge Incineration, and Other Combustion Sources

Any stationary source where semi-volatile inorganic or organic species may pass through control devices in the vapor phase.

Testing Items

The core deliverable of the test is the CPM mass concentration, expressed in mg/m³ (dry basis, standard conditions, often converted to a reference oxygen content). The following items are typically reported:

• Total CPM mass concentration (inorganic plus organic fractions)
• Inorganic CPM fraction and its composition: sulfate, nitrate, chloride, fluoride, ammonium, sodium, potassium, calcium, magnesium, and trace metals
• Organic CPM fraction, with optional speciation by GC-MS
• Paired filterable PM measurement (total FPM, or PM10/PM2.5 per EPA Method 201A or GB/T 16157)
• Calculated total particulate matter emission (TPM = FPM + CPM)

Testing Methods

Sampling Principle

Flue gas is extracted through a nozzle and heated probe, and filterable PM is removed by a heated filter maintained at approximately 120 °C. The gas stream then passes through a water- or air-cooled condenser and dry impingers held in an ice bath, where it is chilled below approximately 30 °C so that condensable species and moisture condense and are captured on the condenser walls, impingers, and connecting glassware.

Reference Methods

• US EPA Method 202 — Determination of Condensable Particulate Emissions from Stationary Sources, based on condenser/impinger collection, nitrogen purge, and sequential water and hexane extractions
• HJ 1077-2019 — Determination of condensable particulate matter from stationary pollution sources (dry impinger method), widely applied in ultra-low emission programs in China

Field Sampling Procedure

• Perform leak checks, metering system calibration, and selection of sampling points per the applicable traverse standard
• Extract flue gas through the heated filter for the required run time (typically at least one hour, or a minimum dry gas volume of approximately 0.85 dry standard cubic meters per EPA Method 202)
• After sampling, purge the condenser and impingers with high-purity nitrogen (for example at approximately 14 L/min for at least one hour per EPA Method 202) to strip dissolved SO2 and eliminate positive sulfate bias
• Recover the train contents: water rinses collect the inorganic CPM, and n-hexane extractions collect the organic CPM

Laboratory Analysis and Calculation

The aqueous (inorganic) fraction is evaporated and dried to constant weight at 105 °C, while the hexane (organic) fraction is evaporated at low temperature and dried; both residues are weighed on an analytical balance with 0.1 mg readability. The CPM concentration is calculated as the sum of the inorganic and organic residue masses, corrected for blanks, divided by the sampled dry gas volume in standard cubic meters. Results are commonly converted to a reference oxygen concentration, for example 6% O2 for utility boilers, for regulatory comparison.

Quality Assurance and Quality Control

• Full train leak checks before and after every sampling run
• Field blanks and reagent blanks to correct for background contamination
• Parallel duplicate sampling runs with defined relative-deviation acceptance criteria
• Calibrated dry gas meters, orifices, thermocouples, and pressure gauges
• Controlled condenser and impinger temperatures with verified nitrogen purity
• Gravimetric determinations performed to constant weight in a controlled-environment balance room

Applications

CPM mass concentration data support a wide range of engineering, regulatory, and scientific objectives:

• Ultra-low emission performance verification for coal-fired power plants and industrial boilers
• Effectiveness assessment of air pollution control devices, including WFGD, WESP, scrubbers, and condensation-type polishing systems
• Environmental impact assessments, emission permitting, and compliance demonstration
• Emission inventory development and ambient PM2.5 source apportionment studies
• Research and development of CPM control technologies such as phase-change condensation, adsorption, and low-temperature electrostatic precipitation
• Academic and regulatory investigations of secondary aerosol formation from stationary sources

FAQ

What is the difference between condensable and filterable particulate matter?

Filterable PM is captured on a heated filter at stack temperature, whereas condensable PM passes through that filter in the vapor phase and condenses only after the gas cools below stack temperature. Total PM emission is the sum of both fractions.

Why is the sampling train purged with nitrogen after sampling?

Flue gas SO2 dissolves in the collected condensate and can subsequently oxidize to sulfate, producing a false positive. Purging with high-purity nitrogen removes dissolved SO2 so that the weighed residue represents true condensable particulate matter.

In what units are the results reported?

Results are reported as CPM mass concentration in mg/m³ or mg/Nm³ on a dry, standard-condition basis, frequently converted to a specified reference oxygen content; the inorganic/organic split is also provided.

How low a concentration can be measured?

With adequate sampled volume and well-controlled blanks, concentrations on the order of 0.1 to 0.5 mg/m³ can be quantified; actual detection capability depends on sampled volume, blank levels, and balance precision.

Can CPM be monitored continuously?

Semi-continuous dilution-condensation type analyzers are available for trending and process optimization studies, but regulatory compliance testing still relies on the reference impinger methods such as EPA Method 202 and HJ 1077-2019.

Is isokinetic sampling required?

When CPM is measured together with filterable PM, for example using EPA Method 201A, isokinetic sampling is required. When only the condensable fraction is targeted, constant-rate sampling is generally acceptable because CPM behaves as a vapor in the stack.