What does it take to make a room (or car, or cupboard) smell good?
Air-fresheners may seem simple enough: they’re a perfume that spreads across a space, via aerosol, slow-release tablet or plug-in diffuser.
They do rely on some clever science to get the job done, though. A particularly tricky aspect, for instance, is controlling the scent-release curve.
At their core, all air-fresheners revolve around volatile organic compounds, tiny scent molecules that are infused into a base and evaporate into the air when released.
How long we can smell a volatile compound depends largely on its chemical structure. Some evaporate in seconds (typically, small, light molecules such as those released by citrus produce). Others last minutes or hours (heavier molecules such as those from wood, musk or vanilla).
To strike the right balance, manufacturers either select fragrance molecules with different volatilities, or deploy a stabiliser. To make a fast-evaporating fragrance such as citrus last longer, for instance, it may be embedded in a slow-evaporating gel or wax, or in polymer beads, which then choreograph how the scent unfolds.
Among brands that use minimal additives, fragrances with different volatilities are combined. Citrus is often paired with a woody or musky scent; which is why organic brands offer aromas such as cedarwood and patchouli or cinnamon and vanilla.
Heat, incidentally, can play a key role. Warmth gives molecules kinetic energy, helping them spread faster. This is why plug-in warmers tend to have a far stronger effect than a simple spray.
Scent delivery is only half the story, though.
A really good air-freshener can do more than infuse a space and mask odours; it can target odour molecules too. Odour-neutralising technology uses substances such as activated carbon, volcanic ash and silica gel to act as molecular sponges, absorbing odour molecules from the air. Certain synthetic enzymes can do this too. These are effective options for bathrooms and kitchen-adjacent areas; for people with sensitivities or allergies; or for homes with infants or pets in them.
Many air-fresheners combine the two approaches, releasing scents and neutralising odours. In such cases, to prevent the deodoriser from absorbing the desirable fragrances, the former is designed to target heavier, stickier molecules containing sulphur or nitrogen (which are the culprits behind fishy, sweaty and garbage-like smells).
Expensive air-fresheners aren’t the only way to brighten up the fragrance profile of a space, of course. Traditional incense sticks or agarbattis release aromatic smoke. Simmer pots are a cosy option; simply heat citrus peels, herbs or spices in water to release aromatic oils into the air. An open bowl of vinegar or baking soda can work as an odour-absorber too.
Sometimes, the simplest solution is the healthiest: just open the windows, air out the room, and, for a long-term deodorising effect (and so much else besides), add a few plants to the decor.
(To reach Swetha Sivakumar with feedback, email upgrademyfood@gmail. com. The views expressed are personal)
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