The usual cocktail of nitrous oxides, sulphur dioxide and hydrocarbons swirling around Britain's airports has just been augmented by a strong whiff of indignation.
Willie Walsh, the chief executive of British Airways, used a conference in Ireland earlier this month to fire off a bullish defense of his industry.
"While it is crucial that aviation takes action on emissions, the notion that flying is a selfish, antisocial activity that single-handedly threatens planetary catastrophe bears no relation to the evidence," he said.
He is not the only airline boss to have challenged the claims of the environmental lobby in recent weeks. Flybe's chief commercial officer tore into "misinformed environmentalists" who peddle the "myth" that aviation is a major polluter, and easyJet's chief executive, Andy Harrison, shared his outrage.
"Aviation is not the environment's biggest enemy -- not today and not tomorrow," he said.
What triggered these outbursts was a report by the European Low Fares Airline Association (ELFAA) examining how a European Commission proposal for an emissions trading scheme would affect EU economies.
It concluded that aviation is being unfairly blamed for carbon dioxide emissions and that penalizing airlines for them would harm both EU integration and the European economy.
British Airways is not a member of ELFAA, and Walsh said he did want to see a "working international system of emissions trading for aviation" to be introduced as soon as possible.
"This is not a painless option for airlines," he said. "If we increase our emissions, we will have to pick up the bill."
Nonetheless, he added, UK planes only contributed around 0.1 percent of global emissions and it was wrong to imagine that banning flying tomorrow would halt the damage.
Figures like these are a comfort to anyone who flies on business, particularly if they are beginning to wonder whether they ought to make an effort to avoid taking the plane. But are they reliable?
But had environmentalists really overestimated the damage aviation was doing?
On the contrary, said Peter Lockley of the Aviation Environment Foundation, Walsh was grossly underestimating it. The percentage he gave "willfully ignores the non-CO2 effects of aviation" and the fact that carbon dioxide causes more damage when it is released at high altitudes.
Lockley estimates that the "uplift" factor makes emissions 2.7 times more damaging and said his own calculations suggest that aviation accounts for around 13 percent of all the UK's greenhouse gas emissions. Furthermore, for all the improvements in fuel efficiency, the boom in cheap flying means that aviation is the fastest growing source of greenhouse gases.
Walsh wants any emissions trading scheme to discount this "uplift" effect because, he argues, "there is little scientific consensus" about it (another expert put the figure at 2.4). He believes that a simpler scheme would be easier to administer. But Flybe and easyJet are furious at the idea that their newer and cleaner fleets should pay the same penalty as the older jets flown by their rivals.
"We fly brand-new aircraft with some of the highest load factors in the business," Harrison said. "We have always argued for bankrupt inefficient airlines to leave the sector and eliminate the unprofitable flying that is usually done on older, dirtier aircraft."