"Small Molecule VOCs " and "Large Molecule VOCs"

In the field of VOCs (volatile organic compounds), "macromolecule" is a relative concept, usually referring to compounds with relatively high molecular weight within the volatility range, rather than true high molecular weight polymers.

Internationally, VOCs are typically defined based on their boiling points . For example, the World Health Organization (WHO) defines organic compounds with boiling points between 50°C and 260°C as VOCs. This boiling point range itself encompasses molecules ranging from very small to relatively large.

Small Molecule VOCs

These compounds are the most typical and most concerning VOCs in the general sense.

· Molecular weight : Usually low, generally less than 100-150 g/ mol .

· Number of carbon atoms : usually between C2 and C8.

· Boiling point : Low; it is usually volatile at room temperature or slightly higher temperatures.

· Structure and characteristics :

o It has a simple structure, short carbon chains, and few or no branches.

o It is highly volatile and can be rapidly released from the product or material into the air.

o Due to its small size, it is easier for it to enter the alveoli of the lungs through the respiratory tract and enter the bloodstream.

o These are typically species with high chemical reactivity and are key precursors to the formation of photochemical smog such as ozone (O₃) and secondary organic aerosols (SOA).

Common examples:

· Formaldehyde (HCHO): The smallest VOC, it is one of the number one culprits of indoor air pollution.

· Benzene (C6H6), toluene , and xylene (BTX): Widely used as industrial solvents and gasoline additives.

· Ethylene (C2H4) and propylene : Important chemical raw materials, and also plant hormones.

· Acetone (CH3COCH3): A common solvent used in nail polish remover and paint thinner.

· Ethyl acetate : A solvent with a fruity aroma.

Main impacts:

1. Health hazards : Many small molecule VOCs are highly toxic and carcinogenic (such as benzene and formaldehyde). Short-term exposure can cause headaches, nausea, and irritation of the eyes, nose, and throat , while long-term exposure can increase the risk of cancer.

2. Environmental effects : It is a major contributor to the formation of near-surface ozone and PM2.5, and has a significant impact on regional air quality.

(Relative) Macromolecular VOCs

These compounds are sometimes referred to as a neighboring category of SVOCs (semi-volatile organic compounds) or VVOCs ( extremely volatile organic compounds) , though the boundaries are not entirely clear. They possess the volatility of VOCs, but their molecules are larger.

· Molecular weight : Relatively high, typically 150-250 g/ mol or higher.

· Carbon number : usually C9-C16 or more.

· Boiling point : High; it typically volatilizes significantly only at higher ambient or operating temperatures.

· Structure and characteristics :

o It has a more complex structure, longer carbon chains, and may contain benzene rings or multiple functional groups.

o It has low volatility and a slow release rate, but its effect lasts a long time.

o Due to their large molecular weight and low volatility, they are more likely to adsorb onto airborne particulate matter, dust, and object surfaces such as walls, furniture, and textiles.

o It remains in the environment for a longer period of time.

Common examples:

· Naphthalene (C10H8): The main component of camphor balls.

· Polycyclic aromatic hydrocarbons , such as anthracene and phenanthrene : originate from incomplete combustion, and some are highly carcinogenic.

· Some plasticizers , such as phthalates (e.g., DEHP), are used to soften PVC plastics and are slowly released from the product.

· Some pesticides , such as DDT (although now banned, it is a typical SVOC).

· Aldehydes with a high carbon number , such as nonanal and decanal ( often considered SVOCs).

Main impacts:

1. Health hazards : Although the acute toxicity may not be as strong as some small molecule VOCs, many large molecule VOCs are endocrine disruptors (such as phthalates), have bioaccumulation, and long-term exposure poses potential risks to the reproductive and developmental systems.

2. Indoor pollution : These are the main causes of "indoor chemical dust." Because they adhere to dust and object surfaces, they are difficult to remove completely through ventilation, forming a continuous source of pollution.

Summary of Key Differences

Conclusions and Implications

Understanding the differences between small-molecule and large-molecule VOCs is crucial for effectively managing and controlling their risks.

· For small molecule VOCs : the key to control is to eliminate them at the source (using low VOC products) and improve ventilation , because they are released quickly, and ventilation is an effective way to quickly reduce their concentration.

· For large molecular VOCs , control is more complex. In addition to source control, regular cleaning (removing toxic dust) and the use of air purifiers (with activated carbon and HEPA filters) are also required to remove particulate matter and gaseous pollutants from the air.

In summary, both small-molecule and large-molecule VOCs pose threats to human health and the environment, but their modes of action, durations, and main risk types differ. When assessing indoor air quality or environmental exposure risks, both types of substances need to be considered comprehensively .