Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants widely present in ambient air, primarily generated by the incomplete combustion of fossil fuels, biomass, and industrial processes. Detection of atmospheric PAHs is essential for air quality assessment, regulatory compliance, and public health protection, as several PAHs such as benzo[a]pyrene are classified as carcinogenic to humans. This article provides a comprehensive overview of atmospheric PAH testing, including sample types, target analytes, analytical methods, relevant standards, and practical applications.
Technical Overview
Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds composed of two or more fused benzene rings. They are ubiquitous atmospheric pollutants formed mainly through the incomplete combustion of organic materials, including coal, petroleum, natural gas, wood, and biomass. Major emission sources include motor vehicle exhaust, industrial combustion processes, coking operations, petroleum refining, residential heating, open burning, and cigarette smoke.
In the atmosphere, PAHs exist in both the gaseous phase and the particle-bound phase, with their distribution governed by vapor pressure and ambient temperature. Lower-molecular-weight PAHs such as naphthalene and phenanthrene tend to partition into the gas phase, while higher-molecular-weight compounds such as benzo[a]pyrene, benzo[g,h,i]perylene, and indeno[1,2,3-cd]pyrene are predominantly adsorbed onto fine particulate matter such as PM2.5 and PM10. This dual-phase behavior requires sampling strategies that capture both phases simultaneously.
Many PAHs are toxic, mutagenic, and carcinogenic. The International Agency for Research on Cancer (IARC) classifies benzo[a]pyrene as a Group 1 human carcinogen, and several other PAHs are classified as probable or possible carcinogens. Due to their severe health and ecological impacts, sixteen PAHs have been designated as priority pollutants by the United States Environmental Protection Agency (US EPA), and they are regulated under ambient air quality standards in many jurisdictions. Accurate detection and quantification of atmospheric PAHs therefore play a critical role in environmental monitoring, exposure risk assessment, and pollution source apportionment.
Testing Samples
Atmospheric PAH testing can be performed on a variety of air matrices depending on the monitoring objective, the sampling environment, and the applicable regulatory framework. Accredited third-party laboratories typically accept the following sample categories.
Ambient (Outdoor) Air
Ambient air samples are collected at urban, suburban, industrial, rural, or background monitoring sites to evaluate regional air quality and compliance with national ambient air quality standards. Sampling is generally conducted using high-volume or medium-volume air samplers equipped with quartz fiber filters for particle-bound PAHs and polyurethane foam (PUF) cartridges or sorbent tubes for gaseous PAHs.
Indoor Air
Indoor air samples are collected in residential, office, school, and public environments to assess human exposure associated with cooking, heating, smoking, incense burning, and infiltration of outdoor pollutants. Indoor sampling typically employs low-flow or passive sampling techniques combined with sensitive instrumental analysis.
Workplace and Occupational Air
Air samples from occupational environments such as coking plants, aluminum smelters, asphalt production facilities, coal tar processing sites, and refineries are tested to verify compliance with occupational exposure limits and to protect worker health.
Stationary Source Emissions
Flue gas and exhaust emissions from industrial stacks, incinerators, and combustion facilities are sampled using stack sampling systems to determine PAH emission concentrations and to evaluate the performance of pollution control equipment.
Deposition and Particulate Samples
In addition to direct air sampling, total suspended particulates (TSP), PM2.5, and PM10 filter samples collected for routine monitoring programs can be analyzed for particle-bound PAHs to support air quality research and source apportionment studies.
Testing Items
Testing programs generally target the sixteen US EPA priority PAHs, which serve as the benchmark analyte list worldwide. Individual compounds can also be tested according to specific regulatory or research requirements.
- Naphthalene
- Acenaphthylene
- Acenaphthene
- Fluorene
- Phenanthrene
- Anthracene
- Fluoranthene
- Pyrene
- Benzo[a]anthracene
- Chrysene
- Benzo[b]fluoranthene
- Benzo[k]fluoranthene
- Benzo[a]pyrene
- Indeno[1,2,3-cd]pyrene
- Dibenzo[a,h]anthracene
- Benzo[g,h,i]perylene
In addition to individual compound concentrations, laboratories often report derived indicators such as the total concentration of the sixteen priority PAHs (ΣPAH16), the carcinogenic PAH fraction, and the benzo[a]pyrene-equivalent carcinogenic potency (BaP-TEQ), which is widely used for health risk assessment. Diagnostic concentration ratios between specific PAH pairs, such as fluoranthene to pyrene and indeno[1,2,3-cd]pyrene to benzo[g,h,i]perylene, may also be calculated to support pollution source identification.
Testing Methods
Sampling
Representative sampling is the foundation of reliable PAH analysis. Active sampling using high-volume air samplers is the most common approach, in which airborne particles are retained on quartz fiber or glass fiber filters while gas-phase compounds are trapped on PUF plugs or XAD resin cartridges positioned downstream. Sampling durations typically range from 24 hours for ambient monitoring to shorter periods for occupational assessments, with flow rates calibrated before and after each run. Field blanks, trip blanks, and surrogate standards are included to monitor contamination and recovery throughout the sampling chain. Because PAHs are photosensitive, samples are protected from light and stored at low temperature during transport to the laboratory.
Sample Preparation
Filters and sorbents are extracted using techniques such as Soxhlet extraction, ultrasonic extraction, or accelerated solvent extraction (ASE), with dichloromethane, acetonitrile, or hexane-acetone mixtures as extraction solvents. The extracts are then concentrated, solvent-exchanged, and purified through silica gel, alumina, or florisil solid-phase extraction columns to remove interfering matrix components. Isotopically labeled internal standards are added to correct for losses during extraction and cleanup.
Instrumental Analysis
The two principal analytical techniques for atmospheric PAH determination are gas chromatography-mass spectrometry (GC-MS) and high-performance liquid chromatography with fluorescence detection (HPLC-FLD). GC-MS offers excellent selectivity, confirmation capability through mass spectral libraries, and simultaneous quantification of all sixteen priority PAHs, making it the preferred method for comprehensive analysis. HPLC-FLD provides high sensitivity for heavier PAHs and is particularly suitable for benzo[a]pyrene determination. Detection limits at the picogram to nanogram per cubic meter level are routinely achievable with modern instrumentation.
Quality Assurance and Relevant Standards
Quality control measures include calibration verification, continuing calibration checks, method blanks, matrix spikes, duplicate analyses, and surrogate recovery evaluation, ensuring that reported data meet defined accuracy and precision criteria. Testing is performed in accordance with internationally and nationally recognized standards, including US EPA Method TO-13A for PAHs in ambient air by GC-MS, US EPA Method 8270 for semivolatile organic compounds, ISO 16362 for particle-phase PAHs in ambient air by HPLC, ISO 12884 for ambient air monitoring, and applicable national standards such as the Chinese environmental protection standards HJ 646 and HJ 647 for the determination of PAHs in ambient air and exhaust gas by GC-MS and HPLC respectively. Benzo[a]pyrene is also regulated as a criterion pollutant in the Chinese ambient air quality standard GB 3095.
Applications
Atmospheric PAH detection serves a broad range of regulatory, industrial, scientific, and public health purposes across multiple sectors.
- Ambient air quality monitoring and compliance verification against national and regional air quality standards
- Environmental impact assessments for construction projects, industrial facilities, and transportation infrastructure
- Occupational exposure monitoring in coking, smelting, refining, asphalt, and combustion-related industries
- Stack emission testing and pollution control device performance evaluation at stationary sources
- Indoor air quality investigations in residential, commercial, and institutional buildings
- Epidemiological and public health studies linking air pollution exposure to respiratory and cardiovascular disease
- Pollution source apportionment and atmospheric transport research using PAH diagnostic ratios and receptor modeling
- Baseline and long-term trend monitoring for air quality management programs
- Emergency response and contamination incident investigations
FAQ
What are the main sources of PAHs in the atmosphere?
Atmospheric PAHs originate primarily from the incomplete combustion of fossil fuels, biomass, and other organic materials. Key sources include vehicle exhaust, coal-fired power plants, coking and steel production, residential wood and coal burning, forest fires, waste incineration, and cigarette smoke.
Why is benzo[a]pyrene used as an indicator compound?
Benzo[a]pyrene is one of the most thoroughly studied PAHs and is classified by IARC as a Group 1 human carcinogen. Its concentration correlates well with total carcinogenic PAH levels in many environments, making it a widely adopted indicator for regulatory limits and health risk assessment.
How low can atmospheric PAH concentrations be measured?
With high-volume sampling and GC-MS or HPLC-FLD analysis, method detection limits in the range of fractions of a nanogram per cubic meter or lower are routinely achieved, sufficient for background-level monitoring as well as compliance testing near emission sources.
Why must both gas-phase and particle-phase PAHs be sampled?
PAHs partition between vapor and particulate phases depending on their volatility and ambient conditions. Capturing only one phase would systematically underestimate total atmospheric PAH concentrations, so combined filter and sorbent sampling is required for accurate total PAH determination.
How should air samples for PAH analysis be stored and transported?
Because PAHs are susceptible to photodegradation and volatilization losses, collected filters and sorbent cartridges should be wrapped in pre-baked aluminum foil, placed in light-tight containers, kept cold with ice packs or refrigeration, and delivered to the laboratory as quickly as possible for analysis.