Emissions of ammonia have been on the rise in the UK, new statistics from the government show, even while the amount of other pollutants entering the atmosphere has fallen.

Levels of the powerful air pollutant rose by 3.2% from 2015 to 2016, the latest year for which statistics are available, according to a report published by the Department for the Environment, Food and Rural Affairs on Thursday morning. The rise came despite an overall fall of 10% in ammonia emissions since 1980.

Most emissions of ammonia come from agriculture, in the form of a gas produced by slurry or other rotting farm waste and fertiliser. It is a cross-border pollutant as it can be carried on the wind. In itself, ammonia is only harmful at relatively high concentrations, when it can cause agricultural accidents such as farm workers passing out in or near slurry containers. But in the air it is regarded as a powerful pollutant because of its capacity to combine with other pollutants in the atmosphere to create very small particles, known as PM 2.5, which can be highly harmful to the lungs when inhaled – particularly by people who are already vulnerable.

However, despite the rise in ammonia, emissions of PM 2.5 were down by 3.7% in 2016, to the lowest level on record. Emissions of larger particles known as PM10 were down by 1.9% over the year.

The potential causes of the increase in ammonia emissions are not covered in the report, but they are likely to be related to agricultural practices. Farmers can help to reduce emissions by the way in which they store slurry and use it as a fertiliser. Scientists are also working on methods to absorb ammonia emissions in the atmosphere, and a team of researchers at Queen’s University in Belfast recently received £250,000 towards such work.

Even as ammonia emissions have risen, levels of certain other potentially harmful substances have fallen. Sulphur compounds, nitrogen oxides and volatile organic compounds are all down, in the case of sulphur dioxide – often a byproduct of burning coal, and the major cause of acid rain – falling by 29% to its lowest level since 1970, when the current series of records began. Nitrogen oxides fell by 10%, and non-methane volatile organic compounds by 2%.

Laurie Laybourn-Langton, director of the UK Health Alliance on Climate Change, said: “The overall decrease in air pollutant emissions is a positive trend, which indicates that efforts to improve air quality are continuing. However, this process is occurring too slowly in the UK and although various bodies have set ‘acceptable’ limits for certain pollutants, no level of exposure is entirely safe. In particular, infants and children are at risk as their hearts and lungs are still developing. Stronger measures, such as increased investment in active transport and the expansion of Clean Air Zones nationwide, would lead to cleaner air across the UK, ultimately improving public health and reducing costs to the NHS.”

Mark Sutton, environmental physicist at the Centre for Ecology and Hydrology, said the trend in ammonia emissions was “no surprise as the UK has very little by way of policies to reduce ammonia emissions”. Part of the rise was likely to be from larger diary herds, linked to the end of EU milk quotas in 2015, a trend also seen in other parts of Europe, and increased fertiliser spreading.

Prof Sutton pointed out that some other parts of Europe have for years made it compulsory to reduce ammonia from manure spreading, and Germany committed last year to regulations on using urea fertiliser. “As car fleets have been adapted for low-emissions, ammonia has become a Cinderella issue that has been long neglected,” he said.

Richard Skeffington, professor of geography and environmental science at the University of Reading, said the data raised questions on farm practices. “So what are large dairy farmers doing wrong? Are farmers using more nitrogen fertiliser and why?” he asked, adding that the report did not provide answers.