The Swedish MBA student who traveled to Ahmadabad in November 2014 discovered the air quality in India's fifth most populous city was a million miles away from that of Scandinavia.
"I was excited to go but when I got there what really struck me was the poor air quality -- the smell in the air, especially going through traffic," Hjertström told CNN. "I might be a bit ignorant, coming from Sweden, but I didn't realize how bad the air is."
It took a while for the penny to drop, but after bouts of headaches and coughing he realized that his childhood asthma
His initial attempts to address the problem with a surgical mask only ended in frustration.
"I remember the first day I was traveling on a train," he recalls, "and all I wanted to do was to rip off the mask because it was so uncomfortable."
Determined to find a solution, he scoured the market for a mask that would provide both protection and was comfortable to wear, but with little luck.
"There were a few brands that were more designed but a lot of them were quite trivial technically and the ones that were really reliable were designed for the industrial sector -- that's when I realized the opportunity."
Partnering with three friends back home, Hjertström launched the company Airinum
, using crowdfunding site Kickstarter to raise $70,000.
With the help of Swedish air filter experts, Camfil
and clothing designers, Hjertström and his co-founders have crafted a product that they believe is both functional and fashionable.
"What separates the mask from others on the market is its shape," the 29-year-old says.
"It's a 3-D construction without being a hard shell -- it fits a lot of faces well," he explains.
"The ability to change filters and the ventilation is also unique. In general, we have improved every aspect of other masks we could find but we haven't done anything radical to the product."
Filtering and fit are the key to an effective pollution mask, says Benjamin Barrett, a lecturer in Air Quality Science at King's College, London
"Generally speaking, there are two reasons why mask can or can't work -- one is the size of the particles they are able to filter out and the other is the fit on the face. If it's leaking in from the side it's not going to work," Barrett told CNN.
"You've got to get a balance between comfort and filtering."
When measuring the amount of pollution in the air, scientists refer to particulate matter
, also called PM followed by a number relating to its size.
"It's any form of particle which are small enough to be breathed into the body," Barrett explains. "We sometimes call it PM 2.5 -- [which has a diameter of 2.5 micrometers] and is small enough to get down into the lungs."
"Chemically, that can be all sorts of different things depending on where they've come from. Any combustion process produces particles whether it's vehicles, heating for the home -- power generation will produce them.
"Also, other processes in the atmosphere create particles by reaction -- that's called secondary particles. Some of the gases vehicles produce, react in the atmosphere and form nitrates, liquid particles rather than metal or carbon particles."
WHO estimate that air pollution contributes to three million deaths annually.
"There's evidence that people living in higher pollution areas have smaller babies
and those children grow up with smaller lungs," Barrett says.
"So they have a start in life that makes them less able to cope with other diseases that may develop later in life, particularly respiratory ones.
"It's a quite a subtle hidden form of harm ... it's something that slowly affects you throughout your whole life."
The global air pollution picture is mixed. While the air in most European cities is far from pure -- London
, Paris and Berlin
all hover above the safe levels recommended by WHO -- their problems are dwarfed by the statistics in Asia.
The Chinese capital, Beijing -- currently experiencing an air pollution red alert
-- has an annual average 8.5 times above
WHO's recommended safe levels. In Delhi and Ahmadabad things are even worse with annual air pollution running at more than 12 and 10 times respectively above what WHO considers safe.
There are a range of contributors to Asia's pollution, Barrett says.
"Power generation is a huge contributor and industry also. There are lot of vehicles now in China although they tend to be relatively new and relatively clean compared with some other countries.
"But you've also got some of the rural areas burning biomass -- coal, wood or other forms. This floats around the atmosphere like a cloud so you tend to get cycles of high pollution followed by clear skies."
Back in Sweden, Hjertström and colleagues are still focused on the Asian market, hoping that their masks can help shield people from air pollution's worst effects.
At $75 for an adult mask and $65 for a kids' version, Airinum's mask is more than double the price of more established brands like Vogmask
and Cambridge Mask
, but unlike its competitors, the filters -- two are included when you buy a mask -- can be removed and replaced with new ones.
"The real goal now is to get the product out on the market to more people and to get as much feedback as possible from the users so we can keep iterating and improving the product,' he says.
"We want to make it the best face mask for people who want to breathe the cleanest air."