Motorists have been asked to forgo unnecessary journeys due to concerns high levels of air pollution in Derry may aggravate symptoms for people suffering with bronchial or pulmonary conditions.
The Department of Agriculture, Environment and Rural Affairs (DAERA) has reported that high levels of air pollution (particulate matter) are currently being monitored in Derry.
The pollution is likely to persist overnight and into tomorrow (Monday), with the situation improving from tomorrow evening onwards.
The high levels of sooty toxins - such as sulphur dioxide, nitrogen dioxide, ozone and carbon monoxide - are caused by traffic and cars idling at junctions and by the combustion of home heating oil.
The current cold spell means it takes longer for these particulates - which medical experts like the Royal College of Physicians (RCP) believe are a contributory factor in thousands of premature deaths in Ireland and Britain each year - to dissipate.
During periods of high air pollution the symptoms of people with lung or heart disease may worsen.
Healthy people are unlikely to experience any ill effects, said DAERA.
In a statement DAERA said: "We can all contribute to reducing the current high levels by avoiding burning solid fuels if possible, by burning only smokeless fuels in smoke control areas.
"Road vehicles are a major source of many pollutants in urban areas. Before using your car ask yourself - do I really need to make this journey? Do I really need to use the car, or could I walk or cycle?
"If you must drive, switch off the engine if you expect to be stationary for more than a couple of minutes, and drive smoothly - it will save you fuel and money and you will emit less pollution."
Back in November new research from the RCP identified Derry as one of 44 cities in the United Kingdom in breach of recommended World Health Organisation (WHO) guidelines for air quality in 2016.
Hourly updates on levels of particulate matter (PM10 and PM2.5), sulphur dioxide, nitrogen dioxide, ozone and carbon monoxide are available on the Department’s website: www.airqualityni.co.uk and the Department’s freephone helpline 0800 556 677, which also offers health advice to those who may be particularly sensitive to air pollution.