On-site condensable particulate matter (CPM) testing quantifies the portion of stack emissions that exists in the vapor phase at flue gas temperature but condenses into liquid or solid particles once the gas cools and dilutes in the ambient atmosphere. Field testing, typically performed in accordance with US EPA Method 202 and consistent with GB/T 16157 and ISO stationary-source sampling conventions, is essential for characterizing total particulate emissions from power plants, iron and steel works, waste incinerators, cement kilns, and other industrial sources. This article explains the technical principles, field sampling procedures, measurable parameters, quality control requirements, and typical applications of CPM on-site detection.
Technical Overview
Condensable particulate matter (CPM) is defined as material that is present in the vapor phase at stack gas conditions but that condenses, nucleates, or reacts to form liquid or solid particles after the flue gas leaves the stack and is cooled and diluted in the ambient air. By contrast, filterable particulate matter (FPM) exists as discrete particles at stack temperature and is retained on a heated filter during conventional sampling. Because CPM passes through a hot filter and only condenses below its dew point, it is invisible to routine in-stack filtration methods and to standard continuous emission monitoring systems for dust.
Chemically, CPM is typically composed of sulfate and nitrate salts, ammonium compounds, chlorides, trace metals, and semi-volatile organic compounds. Upon condensation, this material overwhelmingly falls within the fine and ultrafine size range and is recognized as a significant contributor to ambient PM2.5 and secondary aerosol formation. In facilities operating under ultra-low emission requirements, filterable PM is frequently controlled below 5 to 10 mg/m3, while CPM concentrations may remain in the range of approximately 5 to 20 mg/m3 or higher, meaning that CPM can become the dominant fraction of total particulate discharge.
Total particulate matter (TPM) is therefore calculated as the sum of the filterable and condensable fractions, TPM = FPM + CPM. Accurate determination of CPM requires dedicated on-site sampling using a cooled condensation train, most commonly following the procedures of US EPA Method 202, executed by experienced stack-testing crews or accredited third-party laboratories.
Testing Samples
CPM field detection is applied to the exhaust gas of stationary pollution sources. The characteristics of each gas stream, including moisture content, sulfur dioxide concentration, temperature, and the presence of wet treatment stages, influence sampling design and quality control. Typical sampling points include the stack or flue after the final air pollution control device, such as downstream of a wet flue gas desulfurization absorber or wet electrostatic precipitator.
Coal-Fired Power Plant Flue Gas
Boiler flue gas downstream of selective catalytic reduction, electrostatic precipitation, and wet desulfurization is the most frequently tested matrix. High moisture, residual SO2, and possible ammonia slip from SCR systems require careful artifact control, particularly the nitrogen purge step used to strip dissolved SO2 from collected condensate.
Iron and Steel Process Emissions
Sintering and pelletizing machine-head flue gas, coke oven gas, blast furnace cast-house exhaust, and other steelmaking off-gases are tested to support ultra-low emission evaluation. These streams often contain varied sulfur species, chlorides, and heavy metals that enrich the inorganic CPM fraction.
Municipal and Hazardous Waste Incineration Flue Gas
Waste-to-energy plants and hazardous waste incinerators generate flue gas rich in acid gases, chlorides, and semi-volatile organics. CPM testing at the stack quantifies both inorganic condensables and organic condensables that survive the flue gas cleaning train.
Cement Kiln and Industrial Boiler Exhaust
Cement kiln tail gas, lime kilns, glass furnaces, and gas-fired or biomass-fired industrial boilers are sampled to verify particulate performance, especially where wet scrubbing or condensation-based purification is installed.
Chemical, Petrochemical, and Other Process Vents
Regenerated catalyst vents, drying operations, spray towers, and various chemical process exhausts may carry condensable organics and salts that warrant CPM characterization for permitting and emission inventory purposes.
Testing Items
A complete on-site CPM testing campaign typically covers the following measurable parameters:
- Total condensable particulate matter (CPM) mass concentration, reported in mg/m3 referenced to standard temperature, pressure, and a specified oxygen basis.
- Inorganic CPM fraction, mainly water-soluble salts retained in the aqueous portion of the sample train.
- Organic CPM fraction, comprising solvent-extractable semi-volatile organic condensables.
- Water-soluble ionic speciation of CPM, including sulfate, nitrate, chloride, fluoride, ammonium, sodium, potassium, calcium, and magnesium, determined by ion chromatography.
- Trace metal content of CPM, determined by ICP-OES or ICP-MS where elemental characterization is required.
- Organic composition screening of CPM extracts by GC-MS for research-oriented studies.
- Simultaneous filterable particulate matter, including total FPM and, where required, PM10 and PM2.5 size fractions, enabling computation of total particulate matter.
- Auxiliary stack parameters, including oxygen, moisture, temperature, static pressure, velocity, and volumetric flow, required for isokinetic sampling and result normalization.
Testing Methods
Principle of CPM Field Sampling
The measurement is based on controlled condensation. Flue gas is extracted isokinetically through a heated probe and a heated filter, which retains filterable particulate matter. The gas then passes through a water-cooled condenser that rapidly quenches it below 30 degrees Celsius, typically to approximately 20 degrees Celsius. Within this cooled zone, condensable species nucleate and are captured on the condenser walls, in dry impingers, and on a terminal CPM filter placed downstream of the impingers. Residual moisture is removed by a moisture trap, and the sample volume is measured by a calibrated dry gas meter. The sum of the material recovered from the condenser, impingers, and CPM filter, minus blank contributions, represents the condensable particulate mass.
Field Sampling Procedure
Representative on-site testing generally proceeds through the following steps:
- Pre-test survey of the stack, including determination of stack geometry, moisture, oxygen, temperature, and velocity profiles to establish sampling points and nozzle sizing.
- Assembly and leak check of the sampling train, verification of heated filter and probe temperatures, and cooling water preparation for the condenser.
- Isokinetic sampling, with the sampling velocity maintained within plus or minus 10 percent of the stack velocity, normally for a run duration of about one hour or until the minimum dry gas volume, on the order of 0.85 dry standard cubic meters, is collected.
- Post-run leak check and recording of metering data, followed by a high-purity nitrogen purge of the impinger section to strip dissolved sulfur dioxide and suppress positive sulfate artifacts.
- Sample recovery in the field, with fractions sealed, labeled, and transported under chain of custody for gravimetric and, if required, speciation analysis.
- Performance of a minimum of three valid sampling runs per test condition, in line with accepted stack-testing practice.
Sample Recovery and Laboratory Analysis
During recovery, the condenser, impingers, and connecting glassware are rinsed with water to collect the inorganic fraction, and subsequently rinsed with organic solvents such as acetone, hexane, and methylene chloride to collect the organic fraction; the terminal CPM filter is likewise extracted. The aqueous fraction is evaporated and dried to constant weight at approximately 105 degrees Celsius, while the organic solvent fraction is gently evaporated and dried before gravimetric determination, both using an analytical balance with a resolution of 0.1 mg. The sum of the inorganic and organic residues, corrected for field blanks, yields the total CPM mass. Optional ion chromatography, ICP, and GC-MS analyses provide compositional detail for source characterization and control technology studies.
Quality Assurance and Quality Control
Reliable CPM results depend on rigorous field and laboratory quality control:
- Leak checks of the sampling train before and after each run, with zero leakage tolerance at typical vacuum.
- Collection and analysis of field train blanks and solvent or reagent blanks to correct for background contamination.
- Calibration of the dry gas meter, pitot tube, thermocouples, barometer, and analytical balance against traceable references.
- Verification of isokinetic sampling performance and minimum sampled gas volume for each run.
- Control of dissolved SO2 artifacts through the nitrogen purge, which is particularly important for high-sulfur coal-fired sources.
- Duplicate or parallel sampling where required, with results evaluated against acceptance criteria for relative deviation.
- Complete documentation, including sampling logs, photographs, raw meter data, and chain-of-custody records.
Reference Standards and Applicable Methods
CPM on-site testing is principally governed by the following standards and methods issued by recognized standards organizations:
- US EPA Method 202, Determination of Condensable Particulate Emissions from Stationary Sources, the primary reference procedure for the dry impinger condensation approach.
- US EPA Methods 5, 17, and 201A, covering filterable particulate matter and PM10/PM2.5 determination, used in combination with Method 202 to obtain total particulate emissions.
- GB/T 16157, the Chinese national standard for sampling and determination of particulates from stationary source exhaust, providing the sampling conventions used in conjunction with CPM procedures.
- HJ 836, the Chinese environmental industry standard for the determination of particulate matter at low concentrations, applicable to the filterable fraction of ultra-low emission sources.
- ISO 9096 and ISO 12141, international standards for the determination of particulate mass concentration in stationary source emissions.
- ASTM D6331, covering the measurement of low-concentration particulate matter, and related ASTM and ISO practices for stack sampling quality assurance.
Applications
On-site CPM testing supports a wide range of engineering, regulatory, and scientific objectives:
- Ultra-low emission evaluation and acceptance testing for coal-fired power plants, iron and steel plants, and other industries where CPM limits or characterization are required.
- Performance assessment and optimization of air pollution control technologies, including wet electrostatic precipitators, wet scrubbers, condensation heat recovery systems, and advanced polishing stages.
- Completion verification for environmental impact assessments and support for emission permit applications and renewals.
- Development of emission inventories and particulate matter source apportionment studies at the urban and regional scale.
- Research into secondary aerosol formation and the atmospheric transformation of condensable species.
- Diagnosis of visible plume phenomena, stack rain, and blue or white plume issues caused by condensable emissions after wet treatment stages.
- Baseline and post-retrofit comparisons for plant upgrade projects and technology demonstrations.
FAQ
What is the difference between condensable and filterable particulate matter?
Filterable particulate matter exists as solid or liquid particles at stack temperature and is captured directly on a heated filter during sampling. Condensable particulate matter exists as vapor at stack conditions and only forms particles after the gas is cooled and diluted; it is therefore collected in a cooled condensation train rather than on the hot filter. Total particulate matter is the sum of both fractions.
Why is CPM not detected by routine dust testing or CEMS?
Conventional particulate sampling filters the gas at elevated temperature, so vapor-phase species pass through unmeasured, and optical or beta-attenuation dust monitors installed in stacks respond only to particles already formed. CPM must be measured by deliberately cooling the sampled gas under controlled conditions, which is why dedicated on-site Method 202-style testing is required.
How long does on-site CPM testing take?
A typical campaign comprises three sampling runs, each of about one hour, plus setup, leak checks, nitrogen purge, and sample recovery. Most single-point tests are completed within one working day on site, followed by laboratory gravimetric analysis and reporting, generally within one to two weeks.
What detection capability and result ranges can be expected?
With proper blank control and a 0.1 mg resolution balance, the method can reliably quantify CPM at low single-digit mg/m3 concentrations. Reported values for well-controlled ultra-low emission plants commonly fall between roughly 2 and 15 mg/m3, depending on fuel, process, and treatment train configuration.
Does high sulfur dioxide in the flue gas affect the results?
Yes. Dissolved SO2 in the collected condensate can oxidize to sulfate and create a positive bias. The standard mitigation is the high-purity nitrogen purge performed immediately after sampling, which strips dissolved SO2 before recovery, together with field blank correction.
Who should perform CPM field testing?
Testing should be carried out by accredited third-party laboratories or qualified stack-testing teams with certified personnel, calibrated sampling equipment, and demonstrated experience with condensable particulate methods, since the accuracy of the result depends heavily on field technique and artifact control.
Can CPM be measured continuously?
Currently there is no broadly standardized continuous emission monitoring system for CPM. Condensable particulate emissions are determined through periodic manual on-site sampling, although dilution-based and emerging instrumental techniques are under development to support higher-frequency monitoring in the future.