This week another report on diesel emissions — and, no, we're not talking about Volkswagen and their test-defeating software.

Thankfully, this report is about the potential for liquid nitrogen and cryogenic processes to supplant traditional diesel-driven transport refrigeration units (TRUs) with a zero-carbon emission alternative.

I have written before about how there is a growing advocacy for liquid nitrogen as an alternative in many applications that use conventional vapor compression. But refrigerated transport is a particularly attractive application as a liquid engine can cool the TRU and help power the truck at the same time, harvesting both cooling and shaft power from the same tank of cryogen and creating obvious fuel savings in the process.

One of the main advocates of the cryogenic or "liquid air" approach is British company Dearman, whose Dearman Engine is currently being developed for refrigerated truck rollout next year.

The company appears happy to light a blue touchpaper under the "conventional" refrigeration industry, and last week it released a report on transport refrigeration, with a set of conclusions guaranteed to do just that. The report, "Liquid Air on the European Highway," contends that the diesel-driven TRUs are a source of pollution that has remained unregulated, to the extent that it has become a largely overlooked major threat to European air quality and health.

While Dearman obviously has a vested interest in its exposé of diesel TRU emissions, what its research has come up with is quite astonishing levels of pollution and arguably more astonishing calculations of the cost to society.

"We calculate that switching to this kind of zero-emission refrigeration [i.e., liquid nitrogen] would save 1.9 billion euros per year by 2025 in reduced damage to the environment and health," the authors write. "These reductions in social costs are in addition to any direct financial savings to the owners of the equipment."

Dearman's research found the current 1 million-strong European transport refrigeration fleet will emit 13 million tonnes of CO2e in 2015, which it calculates has an impact on air pollution equivalent to up to 56 million diesel cars.

Equally significant, Dearman says, the lack of standards development in the TRUs has left them trailing far behind the more stringently-regulated road engines — emitting up to 29 times more potentially carcinogenic particulate matter and six times more nitrogen oxides than far larger, modern diesel truck engines. Compared to the best available diesel technology for cars, this rises to an astonishing 165 times greater emission of particulates.

The authors introduce the findings with the assertion that transport refrigeration is "a vital but little noticed pillar of modern society," yet current technology emits both CO2 and what it calls "grossly disproportionate amounts" of toxic nitrogen oxides (NOx) and particulate matter (PM) — pollutants that cause more than 400,000 premature deaths in the EU each year.

By contrast, the authors contend, converting to liquid air would reduce TRU greenhouse gas emissions by 50 percent in 2025 — more if integrated with renewables — and eliminate their emissions of NOx and PM altogether.

The good news, in the authors' eyes, is Europe already has ample infrastructure to support the uptake of cryogenic technology: "We estimate that the 10 countries that operate 80 percent of the EU TRU fleet have enough spare liquid nitrogen production capacity to fuel 70,000 zero-emission TRUs. In other words, the early deployment of liquid air TRUs would require no immediate investment in nitrogen production capacity or distribution networks."

The fundamental problem, the authors contend, is that no one in the policy-making arena is tackling the problem at source. They are either focusing on the refrigerant, via F-gas legislation, or on the road engine.

"Policy around TRUs is currently focused on F-gases, which, although important, account for only 17 percent of aggregate TRU lifecycle greenhouse gas emissions, whereas diesel is responsible for most of the rest, and all of the NOx and PM. Policy should be reset to focus not only on F-gases but on the larger problem of reducing TRU diesel emissions," the report states.

Furthermore, since NOx and PM emissions are especially damaging in cities, TRU emissions should be regulated under Low Emission Zones, the report says.

The problem is exacerbated, the report concludes, by the fact that many major European cities such as Paris and Milan don't collect the data needed to estimate the impact of TRU emissions, so don't know how bad the problem is.

"We recommend that national governments and city authorities should act quickly to improve the quality and granularity of their transport and emissions data," the authors wrote. "You cannot manage what you cannot measure."

Dearman CEO Toby Peters, who is also Chair in Power and Cold Economy at the University of Birmingham, summed up the situation and the potential at the report's launch.

"Until now, nobody has given transport refrigeration units a thought," Peters said. "The impact of transport refrigeration units has never been investigated, let alone addressed. They are unregulated, use outdated, fossil-fueled technology and are disproportionately polluting. What's worse, their pollution is concentrated on city streets where it does the most damage to our health."

In that context, it is no wonder that cooling technology that removes the NOx and particulate emissions, while saving fuel costs for the operator, is starting to attract wider interest — Dearman's cryogenic technology has just won a 2 million pound research grant. It will be interesting to see how well this technology goes down with national governments in Europe — and with the conventional refrigeration industry.