Deadly NOx pollution

 From The Australian Broadcasting Corporation (ABC)

Imagine you're stopped at the lights and two cars pull up beside you. One is a compact SUV, the other a beefy four-wheel drive that weighs twice as much.

The off-roader has a petrol engine, while the SUV has the low idling growl of a diesel.

You'd probably guess the big car is polluting more. 

And you're right, but also wrong.

The smaller car emits less carbon dioxide (CO2) but it also produces more of another form of car pollution — one that has a much greater immediate public health impact than the CO2.

Nitrogen dioxide (NO2) and nitric oxide (NO) are collectively known as the oxides of nitrogen, or "NOx".

Mostly invisible and regularly ignored, NOx is linked to hundreds of premature deaths each year from conditions such as heart and lung diseases.  

Despite this health toll, drivers are generally unable to find out exactly how much NOx their car emits. 

Now, new publicly available data is exposing which popular models pump out more NOx than others.

It comes as a long-anticipated standards update goes into force today that more than halves how much NOx new diesel models sold in Australia may emit.

Here's how these changes may affect your next car — and the air you breathe. 

Unlike with CO2, you won't find a point-of-sale windshield sticker or a vehicle emissions guide that lists NOx pollution.

Cars sold in Australia must emit less NOx than mandated maximums, under rules last updated nine years ago.

These rules are enforced by laboratory testing of new models. Tyres are spun on a giant treadmill while exhaust gases are funnelled, split, and measured.

But lab-testing doesn't necessarily show how much cars pollute on the road.

The Australian Automobile Association (AAA) recently strapped emissions measurement systems onto more than 100 of the most popular cars, utes [pick-up trucks] and vans. They drove these modified vehicles around Geelong in real traffic conditions, following strict protocols for speed and acceleration.

Their testing revealed many cars consumed more fuel and emitted more pollution than lab tests showed.

And some of the biggest discrepancies were for NOx emissions.

The petrol cars were generally under the limit. Two of the 90 petrol cars tested emitted more NOx than the mandated maximum of 60 milligrams per kilometre.

But most of the diesel cars flunked the test.

Seventeen of the 24 diesels tested emitted more than the cut-off limit for commercial or passenger models, which is 280 milligrams per kilometre and 180mg/km respectively (two to three times higher than the limit for petrol cars).

On average, diesel vehicles exceeded their mandated maximums by almost 40 per cent [and remember, the emissions standard for commercial vehicles is 3 - 4 times higher than for petrol cars]

And this wasn't for a new emissions standard. The maximum had been in place since 2016.

Dots on a graph may not look too dangerous, but incremental changes in NOx emissions have a measurable impact on public health, when multiplied by the millions of cars.

If you stand beside a busy road and count the passing cars, about one in every 10 vehicles burn diesel.

Diesel vehicles are less common than petrol ones but emit far more NOx (based on the AAA's data, about 20 times more).

NOx exposure is associated with the majority of deaths from traffic pollution, so the relatively few diesel cars have a disproportionately high public health impact.

Research led by the University of Tasmania's Centre for Safe Air estimates particulate and NOx pollution from traffic leads to more than 1,800 earlier than expected deaths a year.

"Motor vehicles are one of the most important sources of air pollution in Australia," the Centre's director Fay Johnston said.

NO2 is a reddish-brownish gas with an acrid odour, while NO is colourless and odourless.

A near-invisible haze of NOx spreads outwards from highways and suburban streets. Levels drop at about 100 metres to 200m from the source, but remain high in busy traffic areas.

Breathed in, long-term exposure to NOx can damage the lungs and lead to diseases like bronchitis and asthma. It generally inflames and stresses cells in the body, which is linked with heart disease.

"We can measure the increased rates of deaths when NOx pollution is higher," Professor Johnston said.

Despite this high public health impact, Australia has delayed tightening vehicle NOx pollution regulations and is now about a decade behind Europe, the UK and the US.

The AAA's results show a 2024 Toyota LandCruiser Prado (GXL) diesel and a 2024 Mitsubishi Pajero Sport (GSR) diesel have very similar fuel consumption and CO2 emissions.

But the Pajero's NOx emissions are about 17 times higher than the Land Cruiser's.

The reason for this is "after treatment", or the process of cleaning exhaust gases after they come out of the engine.

The most effective method is to inject a nitrogen-rich additive, like AdBlue, into the hot exhaust gases, which converts the NOx into nitrogen gas (N2), water (H2O) and CO2. This is known as selective catalytic reduction (SCR).

The 2022 Toyota Land Cruiser Prado uses SCR, while the 2024 Mitsubishi Pajero Sport does not.

SCR is so effective that it can make a diesel emit as much NOx as a petrol car — and even less than some petrol cars.

Essentially all diesels now sold in Europe use SCR to comply with emissions standards, Shawn Kook, director of the UNSW engine research laboratory, said.

Europe's had these standards since 2015. 

"The technology and products are there," Professor Kook said.

"It is just that [adding this technology] will add costs to car makers."

AdBlue is stocked at petrol stations around Australia. (Getty: John Keeble)

1800 dead per year!  Imagine if it was terrorists or murders!  Over the last 12 months, there were 1361 road deaths in Australia.   There were 227 murders.