Volatile organic compounds (VOCs) and non-methane hydrocarbons (NMHC), among others, are the primary oil‑gas constituents in the atmosphere. The permissible concentration limits for these substances are not fixed values; rather, they are categorized into distinct regulatory frameworks based on the specific application context, the protected receptors, and the objectives of environmental oversight.
Ambient Air Quality Standards
In the broader atmospheric environment, the control of hydrocarbon concentrations primarily relies on ambient air quality standards. These standards are designed to safeguard the ecological environment and public health.
- Non-methane hydrocarbons (NMHC):As a key comprehensive indicator for assessing the concentration of volatile organic compounds in the air, environmental protection authorities typically monitor and evaluate total non-methane hydrocarbon levels within designated areas or during specific time periods.
- Specific volatile organic compounds:For highly toxic hydrocarbon components such as benzene, toluene, and xylene, the standard establishes stringent concentration limits to prevent the formation of secondary pollutants, including photochemical smog.
Indoor Air Quality Requirements
For enclosed or semi-enclosed spaces such as residences and offices, the concentration of volatile organic compounds in the air is directly linked to human health. Indoor air quality standards place particular emphasis on the following aspects:
- Total Volatile Organic Compounds (TVOC):The standard sets a maximum permissible limit for the total concentration of TVOCs in indoor air to assess the overall level of pollution.
- Benzene-series compound restrictions:Due to the potential introduction of hydrocarbon compounds from building materials or external infiltration, the standard imposes stringent concentration limits for specific substances such as benzene and toluene.
Occupational Exposure Limits in the Workplace
In industrial and production settings such as petrochemical plants, oil storage facilities, and gas stations, workers are exposed to a high risk of hydrocarbon vapors. Occupational health standards have established detailed regulations in this regard:
- Time-Weighted Average Permissible Concentration (PC-TWA):It specifies the permissible time-weighted average concentration limits for workers exposed to oil and gas over a standard workday, ensuring that such exposure does not result in acute or chronic health effects.
- Permissible Concentration – Short-Term Exposure Limit (PC-STEL):To address potential short-term fluctuations in hydrocarbon concentrations, a permissible maximum exposure limit has been established to prevent acute irritation or poisoning.
Air Pollutant Emission Standards
To control oil and gas pollution at its source, emission standards for oil storage facilities and petrochemical enterprises mandate oil–vapor recovery and leak‑control measures.
- Organized emissions:It specifies the maximum permissible emission concentrations and emission rates of oil and gas from exhaust stacks.
- Unorganized emissions:Monitoring thresholds have been established for hydrocarbon concentrations at enterprise boundaries or equipment leak points, requiring the implementation of containment, collection, and treatment measures.
Monitoring and Compliance Recommendations
Given that air quality standards for hydrocarbon concentrations encompass multiple dimensions, relevant authorities and individuals should heed the following points when assessing air quality:
- Clearly define the assessment scenario and select the applicable national or local standards.
- Sampling and analysis shall be conducted using certified, dedicated gas detection instruments.
- Regularly monitor the latest updates on standard revisions issued by environmental protection and occupational health authorities to ensure compliance.