Four months into the era of stricter sulphur limits, there was still a question hanging over Europe’s emission control areas (ECAs).

It wasn’t: Will there be enough low sulphur material? (There was)

It wasn’t:  How many shipping lines will close routes ? (Not many)

It wasn’t: Will there be a surge in scrubber installations? (There were orders, but not a surge).

It wasn’t even: Will there be a mass conversion to liquefied natural gas? (Of course not. That would take years.)

Rather, the mystery was: How good was compliance?

Early indications were encouraging. A report from the Swedish Transport Agencysaid that of 60 fuel samples taken from ships in Swedish ports only three were non-compliant.

The European Union’s European Maritime Safety Agency produced similar data. With 500 inspections carried out between January 1 and March 12 in the European ECAs, it heard of only 33 instances of non-compliance, five of them in the Baltic.

Some observers were tempted to conclude that failure to stick to the rules was running at the encouragingly low rate of 3-5%.

Across this came a shadow cast by the Port of Gothenburg. The authorities installed ‘sniffer technology’ on the approaches to the Swedish port. In the first weeks of the year it ‘sniffed’ emission plumes from around 200 vessels and concluded that in 20% of the case the sulphur content was too high.

One sniffer, from one port, is hardly a representative sample of compliance trends across the North Sea, English Channel and Baltic Sea. But even the suggestion that non-compliance could be running at 20% was a chilling thought.

Whatever the scale of rule breaking, the lobby for strict enforcement has some powerful players. Maersk Line, the world’s largest container shipping company, has been at the forefront of those applying non-governmental pressure.

It was warning last year that non-compliance on the part of some players could cause serious economic harm to operators following the rules.

In its latest Sustainability Report, published in February, it repeated its concern that Europe’s ECA enforcement would remain weak. “Non-compliance will harm the competitive landscape and weaken the positive effect on air quality,” it said.

But not everyone sees enforcement pressures as weak. Violating ECA regulations would expose shipowners to serious consequences, according to marine insurerSkuld. It said in January that it was clear the European ECA rules would have teethand that enforcement would be rigorous. It quoted the Danish Ministry of the Environment as saying that new European Union rules would mean member states checking 10% of vessels calling at ECA ports:

A clearer view of ECA compliance maybe only months away. Denmark said in late April that it hoped to have deployed airborne and fixed position detection technology (sniffers) by the middle of this year.

“We hope sniffers can act as ‘speed cameras’ and have deterrent effect”,”  an official told the 36th International Bunker Conference (IBC 36) in Norway.

Ships that appear to be burning non-compliant fuel will be reported to the European Maritime Safety Agency (EMSA). Given time, the mystery of compliance levels will be resolved.