Naphthalene is the simplest polycyclic aromatic hydrocarbon: two benzene rings fused along a shared edge. Unlike most substances discussed as indoor contaminants it is a solid at room temperature, a white crystalline material that sublimes — it passes directly from solid to vapour without melting first. A solid block in a wardrobe or a drain gully therefore fills the air around it with vapour until it is gone.
Naphthalene is the simplest polycyclic aromatic hydrocarbon: two benzene rings fused along a shared edge. Unlike most substances discussed as indoor contaminants it is a solid at room temperature, a white crystalline material that sublimes — it passes directly from solid to vapour without melting first. A solid block in a wardrobe or a drain gully therefore fills the air around it with vapour until it is gone.
By boiling point naphthalene sits within the volatile band of the WHO/ISO classification, which runs from roughly 50–100 °C to 240–260 °C, but near its top, so it partitions readily onto dust and surfaces as well as remaining in the air. As a two-ring compound it is the lightest member of the polycyclic aromatic hydrocarbon family, and behaves quite differently from the heavier, particle-bound members covered on the polycyclic aromatic hydrocarbons page.
Mothballs are the dominant indoor source in the region. Naphthalene blocks, flakes and deodorant cakes are widely sold and widely used in the Gulf — in wardrobes and storage boxes against insects, and as scented blocks in bathrooms, drains and waste areas. A wardrobe or store room containing them is a continuous emission source for as long as the product lasts.
The building fabric contributes a second, slower source. Coal-tar derived products — tar-based damp-proofing, older bituminous membranes, tar-modified paints and some pipe coatings — contain naphthalene, as do bitumen roofing felts and the hot-applied compounds used on podium decks and car park roofs. On a summer roof these warm well past the temperature at which they were laid, and where a fresh-air intake is placed on a bituminous deck, the vapour has a short path indoors.
Combustion and fuel make up the third group. Naphthalene is present in unburned petrol and diesel and in the exhaust from both, so vehicle movements in enclosed parking and at loading bays put it into the air that intakes draw on. Generator exhaust does the same. Tobacco smoke is a further indoor contributor where smoking takes place inside.
Sublimation rate rises sharply with temperature, so a naphthalene block in a store room that is not air-conditioned, or in a wardrobe against an external wall, releases vapour far faster than the same block would in a temperate house. The same applies to bituminous and coal-tar surfaces on roofs and podium decks through the summer. Working the other way, the sealed and mechanically conditioned envelope that keeps the heat out also keeps the vapour in: outdoor air fractions are held low to limit cooling load, and windows are not opened for months at a time.
The characteristic acute effect of naphthalene is on the red blood cell. At high exposure it causes haemolytic anaemia — destruction of red cells faster than the body replaces them — presenting as fatigue, pallor, jaundice and dark urine. Infants and people with glucose-6-phosphate dehydrogenase deficiency, which is common in parts of the population served by Gulf buildings, are markedly more susceptible, and cases in young children following exposure to mothballs or to clothing stored with them are well documented.
At the lower concentrations found in ordinary occupied space, the reported effects are respiratory and irritant: irritation of the nose and throat, and inflammatory change in the airways, which is the endpoint on which the WHO guideline was based.
The International Agency for Research on Cancer classifies naphthalene as possibly carcinogenic to humans. Building complaints usually involve mixtures at low concentration rather than a single compound, and occupants or workers with persistent symptoms — and in particular anyone showing signs consistent with haemolysis — should be referred to occupational health or a medical practitioner.
Naphthalene is collected on a sorbent tube and recovered by thermal desorption with a gas chromatography–mass spectrometry finish, under EPA Compendium Method TO-17 or ISO 16000-6:2021. Because it sits at the upper end of the volatile range, sorbent choice and desorption temperature matter more than for lighter aromatics. Where the heavier polycyclic aromatic hydrocarbons are of interest at the same time, EPA Compendium Method TO-13A, using a PUF or XAD sampler with a GC-MS finish, applies.
A photoionisation detector gives a poor account of naphthalene: it reports a single total response weighted by a response factor and identifies nothing. Sampling placement matters more than usual, because the source is often a small enclosed volume rather than the room.
Naphthalene is unusual among indoor contaminants in having two published values that a UAE report might reach for. Dubai Municipality's Technical Guidelines for Indoor Air Quality for Healthy Life (DM-HSD-GU119-IAQ, Version 4, 11 December 2024) gives naphthalene an individual objective in Table 4 of 10 µg/m³ over 8 hours. The WHO Guidelines for Indoor Air Quality: Selected Pollutants (2010), which cover exactly nine substances and include naphthalene among them, give a guideline of 0.01 mg/m³ as an annual average.
Those two figures are the same order of magnitude, and that resemblance is a trap. They are not interchangeable, because they are not the same kind of statement. An 8-hour objective describes a working day and can be met or missed by a single day's measurement; an annual guideline describes a year of continuous exposure and cannot be demonstrated by an 8-hour sample at all. A single 8-hour result quoted against the WHO annual value is a category error. Any report that uses either figure should print the averaging period alongside it and name which body issued it.
The status of the two also differs. The WHO guidelines are recognised international practice and not law in the UAE — WHO describes them as having the character of recommendations. Table 4 operates under clause 9-8-9 as an alternative compliance route, applied where a sampling point fails the total volatile organic compound criterion. Dubai Municipality's indoor air quality limits for new buildings sit within a voluntary certification route — clause 9-8-3 of DM-HSD-GU119-IAQ Version 4 applies to buildings that optionally apply the procedure — whereas the corresponding provisions for existing buildings, in clause 9-8-4 of the same guideline and clause 401.07 of the mandatory Al Sa'fat green building system, are expressed in mandatory terms.
Naphthalene is one of the few indoor contaminants where source removal is usually simple and complete: mothballs and deodorant blocks can be taken out, the storage space aired, and stored textiles washed or aired before reuse. Where the source is a bituminous or coal-tar surface or an exhaust ingress path, the remedy is a fabric or ventilation change — relocating a fresh-air intake, sealing a route from a car park, or overlaying a membrane. Increased outdoor air dilutes but does not remove a source, and in UAE summer conditions the cooling-load penalty makes it unsustainable as a permanent control. Re-testing should follow under comparable temperature, occupancy and ventilation conditions.
Naphthalene is unusual among indoor contaminants in having two published values that a UAE report might reach for. Dubai Municipality's Technical Guidelines for Indoor Air Quality for Healthy Life (DM-HSD-GU119-IAQ, Version 4, 11 December 2024) gives naphthalene an individual objective in Table 4 of 10 µg/m³ over 8 hours. The WHO Guidelines for Indoor Air Quality: Selected Pollutants (2010), which cover exactly nine substances and include naphthalene among them, give a guideline of 0.01 mg/m³ as an annual average. Those two figures are the same order of magnitude, and that resemblance is a trap. They are not interchangeable, because they are not the same kind of statement. An 8-hour objective describes a working day and can be met or missed by a single day's measurement; an annual guideline describes a year of continuous exposure and cannot be demonstrated by an 8-hour sample at all. Any report that uses either figure should print the averaging period alongside it and name which body issued it. Dubai Municipality's indoor air quality limits for new buildings sit within a voluntary certification route — clause 9-8-3 applies to buildings that optionally apply the procedure — whereas the corresponding provisions for existing buildings, in clause 9-8-4 of the same guideline and clause 401.07 of the mandatory Al Sa'fat green building system, are expressed in mandatory terms.
Dubai Municipality DM-HSD-GU119-IAQ Version 4 (11 December 2024), Table 4 — naphthalene 10 µg/m³ over 8 hours. WHO Guidelines for Indoor Air Quality: Selected Pollutants (2010) — 0.01 mg/m³ as an annual average. The two averaging periods are different and the values are not interchangeable.
No. Dubai Municipality's Table 4 objective is 10 µg/m³ over 8 hours; the WHO 2010 guideline is 0.01 mg/m³ as an annual average. They are close in magnitude but describe different exposures, and an 8-hour measurement cannot demonstrate compliance with an annual guideline.
Yes. Naphthalene blocks and deodorant cakes remain widely sold and used in the region, and because the compound sublimes they release vapour continuously until consumed. An enclosed wardrobe or store room concentrates that release, and stored textiles carry it into the rest of the building.
Yes, the lightest one — two fused rings. It behaves as a vapour rather than as a particle-bound compound, which is why it is sampled and reported differently from the heavier polycyclic aromatic hydrocarbons.