Ozone levels in parts of the Greek capital surpassed recommended safety levels on Sunday, prompting a warning from the Health Ministry.
According to authorities, high ground-level ozone rates were recorded in the suburbs of Liosia, Maroussi, Aghia Paraskevi and Thrakomakedones, all north of the city center.
They warned people with breathing or heart problems, or anyone with sensitivity to pollution, to remain indoors and avoid exposure. Exercise or any other form of over-exertion is also to be avoided, health authorities warned, as it can lead to breathing difficulties.
Athens and other parts of the country have been in the grips of a heat wave since Friday that has seen temperatures in parts passing the 40-Celsius mark. The effects of the heat have been exacerbated by a lack of wind, leading to a spike in pollution levels.
The national weather service has forecast brief showers in parts of the northern Greece on Sunday and Monday, adding that temperatures are expected to begin subsiding as of Tuesday.