On Thursday, August 14, 2025, there is still a chance of smog due to ozone in parts of the provinces of Utrecht, North Brabant, Gelderland, and Limburg. People sensitive to smog may be affected. The RIVM advises them to stay indoors and limit heavy physical exertion. This advice is especially applicable in the afternoon and early evening when the air is most polluted.

Smog due to ozone can lead to an increase in respiratory complaints, such as coughing and shortness of breath, worsening of asthma symptoms, and a decrease in lung function. Eye, nose, and throat irritation can also occur. People with respiratory conditions, children, and the elderly are relatively often sensitive to smog. Contact your doctor if you experience complaints.

Also chance of smog due to ozone on Thursday

The weather patterns are developing differently than expected on Monday, August 11. Due to a persistent southerly flow in the middle of the country, there is a chance of smog in the province of Utrecht, the central and eastern parts of the province of North Brabant, the southern part of Gelderland, and in North Limburg. During the day, the wind shifts to the west and cleaner air is brought in. The ozone concentrations are then likely to be lower and there is no longer a chance of smog. This also applies to the following days.

Smog due to ozone

Smog due to ozone occurs when air pollution accumulates on sunny days. This occurs in spring and summer when there is little (mostly southeasterly) wind. The pollutants, such as nitrogen oxides and volatile organic compounds, are converted into ozone under the influence of sunlight. This is also known as summer smog. In the other seasons, the suns strength is too low to create high ozone concentrations.

European information and alarm thresholds for ozone

In Europe, information and alarm thresholds for ozone have been established. The EU European Union (European Union)-information threshold is 180 micrograms of ozone per cubic meter of air. In case of (impending) exceeding this value, people sensitive to smog may experience complaints. The RIVM then issues a warning. The air quality is then poor according to the Dutch Air Quality Index. 
The EU alarm threshold is 240 micrograms of ozone per cubic meter of air (very poor according to the Dutch air quality index). When this value is exceeded, everyone may experience complaints. If this is about to happen, the RIVM will turn the warning into an alarm.

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