Introduction

Formaldehyde is the simplest aldehyde with the formula HCHO (1 ml/m³ = 1 ppm, which is equivalent to 1,2 mg/m³ at 20 °C and 101,3 kPa). It is a colourless gas with a pungent odour and is highly reactive. Formaldehyde is readily soluble in polar solvents such as water and alcohol and is commercially available mainly as a 35 % to 40 % mass fraction aqueous solution containing 5 % to 15 % mass fraction methanol added as a stabiliser.

Presence in the atmosphere

An important natural emission source is the atmospheric oxidation of methane.

In the tropical earth atmosphere the mixing ratio of formaldehyde is about 1 ppb.

Urban pollution

Formaldehyde is formed during practically all incomplete combustion and other oxidation processes of long-chain organic substances.

High formaldehyde concentrations are often measured during the combustion of biogas, sewage and landfill gases in gas engines. In order for the emission values to comply with the legally stipulated limit values, it is usually necessary to post-treat the exhaust gas.

The outdoor air concentrations in Central Europe is mostly below 0.01 mg formaldehyde/m³

An important source of formaldehyde emissions are incomplete combustion processes. These are found, for example, in combustion engines in motor vehicles, in foundries and in the manufacture of plastic articles.

Indoor pollution

Generally, outdoor sources of formaldehyde are not significant sources of formaldehyde in indoor air. Outdoor air may be contributory only if strong formaldehyde sources (e.g. heavy road traffic) are nearby.

The occurrence of formaldehyde in indoor air is often a consequence of the use of certain wood-based board material for construction and for work on the interior and furnishing of a room. Increased concentrations may also be due to other products, including use of certain disinfectants and paints. Tobacco smoke is an additional important intermittent source of formaldehyde.

What are the sources of HCHO?

Whereas an intermittent emission source (e.g. the use for a limited period of time of disinfectant spray containing formaldehyde) will cause an increased formaldehyde concentration in indoor air for only a short period of time during and after use, a continuous emission source (e.g. a particleboard used for indoor furnishings) will contribute to the formaldehyde concentration over a longer period.

Sources and examples for use:

particleboard and other pressed-wood products:

· walls (outdoors and indoors)

· ceilings

· false ceilings

· floors

· baseboards

· doors and doorframes

· stairs

· plywood panelling

· furniture

urea-formaldehyde foams:

· wall cavity insulation

· roof insulation

adhesives, glue:

· wallpaper pastes

· gluing tiles

· veneer

· panelling

· carpets and vinyl floor

wallpaper, lacquers, varnishes, paints:

· interior decoration

tobacco:

· tobacco smoke

disinfectants:

· sprays and solutions for surface disinfection

combustion processes:

· gas stove operation

treated textiles:

· furnishings

How do HCHO get into the air?

Certain formaldehyde-containing materials (such as wood-based materials, floor coverings, furniture and textiles) can cause contamination of the breathing air in closed rooms by degassing.

Smoking also produces formaldehyde due to incomplete combustion processes, which contributes significantly to air pollution. The total smoke of a single cigarette contains about 0.02-0.1 mg formaldehyde.

The combustion of wood in small combustion plants is also problematic, as here the combustion is often incomplete due to irregular charging or damp wood. In the end, formaldehyde concentrations of 50-100 mg/m³ are produced in these plants used in house operation.

What are the health effects of HCHO?

Formaldehyde occurs in the body as a natural metabolic product and serves as a methyl source. The resulting endogenous formaldehyde concentration in the blood of mammals (rat, primate, human) is 2-3 mg/L blood.

Due to its high water solubility and reactivity, formaldehyde absorbed from the air by primates and humans is metabolised in the nose, a small proportion is also absorbed in the throat, trachea and bronchi due to their nose-mouth breathing.

The irritation of the upper respiratory tract in humans as well as a cytotoxic and animal experimentally proven carcinogenic effect after long-term exposure are the critical effect endpoints of inhaled formaldehyde.

Formaldehyde may cause allergies, skin, respiratory or eye irritation if used improperly. Acute danger to life (toxic pulmonary edema, pneumonia) exists from a concentration of 30 ml/m³. In chronic exposure it is carcinogenic and also impairs memory, concentration and sleep.

Evaluation, guideline and limit values

The recommended World Health Organization (WHO) guideline value for formaldehyde for indoor/ambient air quality is 0,1 mg/m³, expressed as the 30 min average concentration.

How can HCHO be reduced?

Humidity and temperature influence the emission rate of e.g. formaldehyde from particleboard; With increasing humidity and temperature, formaldehyde emission increases considerably

The main action reducing HCHO in indoor air is sufficient ventilation.

How do we measure HCHO?

At Aristoteles Consulting, we measure HCHO with continuously registering measuring devices. This devices are equipped with a Gas Sensitive Electrochemical (GSE) sensor. The measured data are saved by a data logger, which can be read out after the measurement to get information about the concentration and to create data tables and graphs showing time dependent variations.

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