From why you have to show your boarding card at duty free to what happens to lost luggage, plus how celebrities make it on the plane without being spotted, we shine a light on some of the mysteries behind the airport experience.

As you can imagine the heavy air traffic and the various road machinery around airports emit all sorts of nasty chemicals – carbon monoxide, ozone and VOCs included. The air quality around Europe's busiest airport, Heathrow, for example, regularly breaches the legal limit for nitrogen dioxide pollutants.

A study published in the online journal Occupational & Environmental Medicine found an association between people who live close to an airport and an increased risk of heart disease. It found the people who were exposed to the highest noise levels, particularly at night time, were at a greater risk of developing high blood pressure and heart flutters.

Leave – or lose – anything at the airport, and it will go into a storage area where you have up to 90 days to collect it. That includes luggage misplaced by airlines. After that, most airports donate unclaimed items to charities – or even sell them off for cash at huge auction houses. Find out more tips on keeping your luggage safe.

Airports charge airlines big fees for the privilege of landing on their runways on certain days or times, and these ‘landing slots’ are rigorously sold or traded between airlines. For example, in 2016 Oman Air paid Air France-KLM $75 million for a prized early morning arrival slot at Heathrow. The escalating value of these slots in turn bumps up passenger fares – by about £4 per passenger over the last 10 years.

Unless you’re a frequent flyer with the airline or have paid a premium fare for your seat, your chances of an upgrade are pretty much non-existent these days. And it won’t help to dress up, mention that you’re on your honeymoon or ask nicely, either. Even being mates with a pilot doesn't cut it nowadays as getting upgrades for friends and family is a perceived fringe benefit for most airline employees. Want to upgrade your in-flight experience regardless of class? Read our guide here.

If you are luckily enough to be one of the chosen few to get an upgrade – or are using Avios or frequent flyer points to move from economy to business class – don't expect to get the full luxury experience either. You almost always won't have access to the airline's business class airport lounge on this type of ticket, meaning you'll miss out on all that free-flowing fizz and food before you fly or during a layover.

Have a connecting flight? Don’t stock up on duty free booze and perfumes without checking if you’re allowed to bring them through your layover destination with you. Some airports – including many in the US – won’t allow any liquids over 100ml past security checkpoints, even if they’re in sealed bags.

Ever feel like you’re walking forever? Well, you are. According to research by the Association of British Travel Agents (ABTA), passengers at London airports face walks of over half a mile with each visit. London’s Stansted airport has one of the longest distances between check-in and the departure gate with a walk of 3,822 feet. Other long walks include 2,953 feet at Luton airport, 2,697 feet at Manchester and 2,461 feet at Glasgow airport.

Want to save your legs at Heathrow? Well, Martin Thomas, BA’s product brands and customer experience, revealed a top tip in an interview with The Daily Mail. “If you’re arriving at Heathrow from the London Underground or Heathrow Express there’s a quicker way to the Fast Track security lanes, accessible behind the B bank of desks at the northern end of Terminal 5.” Looking for more shortcuts? Check out these maps of Heathrow before your journey.

They’ll rarely announce it as your tardy flight is touching down, but if an EU-based airline (that includes Ryanair, Easyjet and British Airways) arrives at its destination three or more hours late, they owe you cash. The rules are €250 for flights under 1,500km (932 miles), but payments can reach €600 for flights over 3,500km (2,175 miles). Although, it's not payable in “extraordinary circumstances”, which could be anything from war, civil unrest or security issues, to natural disasters, extreme weather, air traffic control restrictions, and crew strikes.

You’ll never get a great rate at the terminal because exchange bureaus prey on those disorganised travellers who have left things to the last minute. If you’ve forgotten to buy your currency in advance, you’ll get far better rates by ordering it online for collection at the airport instead.  Travelex, for example, only needs four hours’ notice for orders. Or go to an ATM at your end destination. If you want to try something a bit different, here's our guide to peer-to-peer currency exchange.

While the selection is often epic and displays hugely enticing for a bored pre-flight mind, with special bottles and large formats not available elsewhere, the truth is that when it comes to the run-of-the-mill stuff duty free isn’t always cheaper. You’ll often pay less for spirits in supermarkets, and luxury brands such as Dior or Chanel are most likely charging the same price as in their own boutiques.

Most airlines allow a cabin bag plus a personal item such a purse or laptop bag – and that’s it. But increasingly some airlines (including Ryanair) only allow a single bag up to 10kg (22 pounds). So whatever you buy at duty free will have to fit inside your single bag, or you may end up having to check your bag at the gate for an additional fee. You could try slipping it in your coat but they're pretty ruthless at the gate.

You might have a famous person on your plane, but you probably won’t know it. Larger airports have separate – sometimes red-carpet – check-ins and security control, and celebrities will often be boarded direct into the plane through a secret door by the jet bridge. What's more, many airlines will whisk VIPs away from prying eyes right at the tarmac – Delta do this in a Porsche, for example, and American Airlines in a Cadillac. Of course this kind of treatment doesn't come cheap...

When flying from the UK to a non-EU country, shops are allowed to claim back from the government the 20% VAT they pay on goods sold. The problem? They don’t always pass on this saving to consumers, with prices typically the same in high street shops as they are at the airport. When savvy British travellers found this out in 2015, a mass revolt occurred when thousands refused to show their boarding passes.

In most cities, you’ll pay a premium to be collected from the airport by a city taxi. In London, black cabs charge an extra £2.80 for journeys beginning in Heathrow; in US cities it’s typically a couple of dollars. If you're pre-ordering a cab be sure to ask their charging policy on delays or you could be in with a very nasty surprise at the end of your trip.

Airlines’ computerised booking systems often throw up pricing glitches, which are available to book until they're spotted and rectified by the airline. Eagle-eyed online shoppers snap them up and some websites such as secretflying.com are dedicated to broadcasting these deals, which means if you're quick you can bag yourself some serious bargains. We've got more tips on how to get cheap flights here.

According to a Which? Travel survey of 850,000 flights earlier this year, only 74% of flights arrive on time. One of the worst culprits is easyJet – one in three of its flights arrived at least 15 minutes late in 2016. Even if your flight took 15 minutes less than you expected, you probably haven’t made up time en route. It’s more likely that the arrival time was adjusted to allow for delays and make airlines look more punctual than they actually are.

Thanks to tricky logistics – including strict security surrounding deliveries – specialist airport restaurant companies are in charge of running the outlets in an airport, not the chefs themselves. That means while you might have a nice meal, it’s probably not going to be as good as it would be if you went to their actual restaurant.

Research shows that Tuesdays and Thursdays are typically the cheapest days of the week to fly. And the most expensive? Unsurprisingly, it’s Friday, Saturday and Sunday. So if you're flexible, be sure to look for midweek options to save a few pennies.

If you check your luggage in late, there’s a very good chance that your bag will be one of the first ones out onto the carousel at the other end. The last bags loaded in the hold for a flight are typically the first ones off, which means yours will come coasting off along with the business class items and you can waltz smugly off to be first in the line for the taxi queue. We've got more insider knowledge from baggage handlers here.

Becoming an air traffic controller is intense, one professional revealed in an interview with The Telegraph. There are three phases to the selection process before successful candidates enrol at the National Air Traffic Services training college. This is followed by on-the-job training before a nail-biting final assessment. But contrary to popular belief it’s not a stressful workplace. “People are always surprised when they come to the tower and see how calm it is," he says. "They imagine this really hectic place where people are screaming and throwing things at each other... But it’s a serene space.”

A worrying discussion among airport employees on Reddit which reveals that some workers aren’t subject to security checks every day. “I go through security maybe twice a month, it’s a joke,” one wrote. However, most of the employees in the discussion say that they are subject to very thorough background checks before getting security clearance.

Some glaring vulnerabilities were discovered in security scanners by researchers from the University of California and the University of Michigan, according to an article on Wired. They found that weapons could be taped and hidden from view and plastic explosives moulded around a person’s body were indistinguishable from flesh in the machine’s images. However, more reassuringly the research was carried out on Rapiscan Secure 1,000 machines, which are no longer used in airports. Let's just hope they were a little more thorough when testing the new ones.

A lot of thought has gone into airport layouts to ensure the flow of travellers. The key to successful airport design is easy navigation, according to an article on Mental Floss. This is achieved through subtle but effective design cues that help people find their way from security to the gate. One way is through signage – many terminals have their own distinct colours and fonts so you know if you’ve wandered too far. In many airports the tarmac is visible as soon as you clear security, which supposedly allows travellers to get their bearings right away.

Airport travellers are prime customers for retailers: a captive audience that’s in a “self-indulgent” mood, according to the Maximising Airport Retail Value report by InterVISTAS. That’s why there is plenty of seating and "dwelling space" in the retail areas. This is known as "revenue seating" and it’s designed to lure passengers into shops while they’re in the so-called “golden hour” – the first 60 minutes after clearing security when they're most likely to buy.

Airport geeks may already know that airport codes are dished out by the International Air Transport Association, but did you know that the letters don’t always stand for something? Los Angeles, for example, simply added an ‘X’ when the codes were changed from two to three letters after the 1930s. Portland did the same to make PDX. You can find out what the letters mean at this website dedicated to airport codes, perfect fodder for quiz nights.