The dense fog and dust that enveloped the city in the early hours on Wednesday hung over the Bosporus from Beykoz, Çekmeköy, Ümraniye and Beşiktaş to Sarıyer, and in the high parts of the European side, resulting in the cancellation of some ferry services.

Due to the high density of the haze, experts warned those with respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD) to take precautions due to the high concentration of small particles of dust.

In large metropolises, it can be difficult to differentiate between pollution-laden smog and fog or mist. Unlike smog, fog is a high concentration of tiny droplets consisting of more than 90% water and very few toxins. It can cut down visibility to less than 1 kilometer (0.62 miles). So, although the occurrence of fog can affect traffic conditions, it does not usually harm people's health.

In contrast, when the air is polluted with dry particles like PM2.5 and PM10 and gases like ozone, nitric oxide, nitrogen dioxide and sulfur dioxide, smog may occur if the relative humidity is less than 80% because nitrogen dioxide and sulfur dioxide may react with tiny water drops in the air and form nitric acid and sulfuric acid. It is widely reported that polluted air has negative effects on human health.

Currently, dry dust haze is one of the main air pollution types that occur most frequently worldwide. Studies show that these adverse effects include increased respiratory symptoms and diseases, aggravation of asthma, and a decrease in lung function.

Professor Hüseyin Toros from the Istanbul Technical University (ITU) Faculty of Aeronautics and Astronautics, Department of Meteorology Engineering told Anadolu Agency (AA) that dust and sand particles floating in the atmosphere over Türkiye in spring are brought by seasonal winds. It descends to the ground with the rain. After the moisture evaporates, the dust on the ground is stirred up and irritates those who breathe it in.

"The dust on the ground is not very dense at the moment. It has not yet descended and is hovering at higher altitudes, so there is not much trouble currently, but people suffering from respiratory diseases must remain cautious," said Toros.

However, with forecasts predicting rainy days this week, Toros said it may mean the risk of dust-laden downpours until Sunday.

Regarding the appearance of the current misty weather, the expert said: "There is currently high-pressure air in Türkiye with a little wind. Fog or haze may occur on the ground from time to time."

Güven Özdemir, Istanbul Aydin University lecturer and meteorological engineer, explained: "The dust and sand coming from the African and Arabian regions can carry the particles to the uppermost layers of the atmosphere with the winds and turn into mud with precipitation. However, the dust coming from the desert is beneficial because it carries minerals, such as copper and zinc, but the dust, which is too small to be seen with the naked eye, bothers people with sensitive respiratory systems. Of course, it will unfortunately adversely affect those with asthma and COPD from time to time."

Özdemir explained that the dust haze occurs mostly in spring due to an increase in convective movements, which create sudden rapid heating on the ground during the day and sudden cooling at night, sometimes with the temperature dropping to zero in this case.

Besides, the dust can result in nose and throat irritation, difficulty breathing, coughing, headaches, dizziness, vomiting, diarrhea or allergic symptoms. People suffering from eyesight issues must be careful while making a contact with eyes as it can cause irritation, said Toros.

While fog and dusty haze in Istanbul increase the rate of pollution in the air and negatively affect human health, it affects aquatic creatures and plants positively, thanks to the minerals it carries.