The air we breathe: The surprising science of bad (and good) smells
In part three of our 'Air We Breathe' series, Michael Daly discovers the surprising evidence about bad smells.
Bad smells in the neighbourhood can be the pits, leaving people feeling frustrated and trapped, unable to open their windows on a warm summer day.
According to the Ministry for the Environment, complaints about odour emissions are one of the most frequent environmental pollution incidents reported to regulatory authorities.
"Odours have the potential to cause significant adverse effects on people's lives and wellbeing," the ministry says in its guide for monitoring odour.
"Odour is complex. The range of adverse effects it can cause varies significantly, as does people's sensitivity..."
Timaru resident Veronica Fellows knows all about the frustrations of being unable to do anything when a bad smell wafts through her part of town. In her case the smell comes from offal and is not new, it's just much more common this summer than usual.
"I have been here for four years and this is the worst it has been," Fellows said.
"The other night, when it was a really sticky day, I tried to open the windows and the stench was out of this world. It turns your stomach."
Environment Canterbury received 62 complaints of a rendering meat products smell in the Timaru area in December and January, and has told a meat processing plant it needs to sort out the problem.
As maddening as regular foul odours can be, our sensitivity to them is seen as an indicator of success in cleaning up our towns and cities.
THE ODD SMELL OF CLEANLINESS
Urban areas used to be full of the smells of animals wandering the streets, and didn't have sanitary sewers or controls on the pollutants coming out of factories, olfactory researcher Pamela Dalton, from the Monell Chemical Senses Center in the US, said.
As cities were able to reduce their smelliness, residents became more sensitive to the bad odours that remained.
Bad smells also became even more offensive when people felt trapped.
"You can't put earplugs in or look away. If you're breathing, you're smelling," Dalton said.
Even odours that might be considered pleasant in limited amounts could become oppressive if they couldn't be escaped. For example, the smell of vanilla or chocolate from an industrial bakery.
WHEN TOWN AND COUNTRY COLLIDE
While rural smells may have been removed from our towns, smelly problems can arise when the town spreads too far into the countryside.
Last April, Havelock North-based Te Mata Mushroom Company, which makes compost, was fined $15,000 for allowing offensive and objectionable odours to waft across a new housing area.
Residents had been shutting themselves up inside their homes with the air condition on full blast, rather than enjoying the long, hot Hawke's Bay summer outside.
Mushroom Company owner Michael Whittaker described the problem as a "rural versus urban collision". Expert guidelines were for separation of at least 500 metres between a compost operation and housing, but houses were being built within 190 metres of the operation's boundary, he said.
DON'T WORRY, SMELL HAPPY
Researchers believe the way odours affect people is based on how we relate smells to past events. Unsurprisingly, studies have also shown that odours people like make them feel good, while odours they don't like make them feel bad.
That led onto how people's moods influenced how they thought and acted, Rachel S Herz, an assistant professor of psychology at Brown University, said.
"Pleasant ambient odours have also been found to enhance vigilance during a tedious task and improve performance on anagram and word completion tests," she said.
"Conversely, the presence of a malodour reduced participants' subjective judgments and lowered their tolerance for frustration."
SMELLS BAD, IS GOOD
Context was also important in how people reacted to smell. So, for example, many people in western countries might react positively to smelly cheese - once they realised what it was - but in parts of Asia it might be considered repulsive.
Blenheim bar manager Kellie Kennedy became less concerned about an offensive odour last November when she realised it was coming from grape marc, a winemaking waste product.
"It's nice to know it's not poo, it's just rotting grapes. It does make it a little bit better because now I know that we are not stepping in anything," Kennedy said.
Then there's Rotorua. What do you do about a place that just naturally smells different?
In the words of famous son and NBA star Steven Adams, as told to ESPN: "It smells like someone farted in your face all the time, but you get used to it."
At least it seems Rotorua residents don't need to worry about the effects of all that low-level hydrogen sulfide (H2S) gas produced by the area's geothermal activity.
A study involving AUT, Otago University, and the University of California at Berkeley found no evidence that exposure at levels present in Rotorua were a risk factor for asthma or asthma symptoms. In fact the levels of the gas found in Rotorua might even help.
The study also found no evidence H2S at Rotorua levels was associated with impairment of cognitive function or mood, or any link with cataracts.
Not all regional councils were able to provide information about odour complaints. Among those who did provide data, Northland Regional Council said that during the past 23 years the number of annual odour complaints had ranged between 121 and 42.
No trends or patterns were obvious, NRC compliance monitoring manager Tess Dacre said. The way complaints were described was also not an exact science. For example, the same incident might be logged as sewage or odour.
Waikato Regional Council logged just over 220 complaints in 2016 where the main concern was categorised as odour. About 40 per cent of those were related to waste disposal, composting and waste recycling facilities.