New Delhi: After showing signs of improvement earlier in the week, Delhi’s air quality once again deteriorated on Friday, slipping into the “very poor” category as wind speeds dropped across the region. The decline in air quality coincided with a slight rise in the minimum temperature, which settled at 7.7 degrees Celsius, reflecting the changing meteorological conditions over the national capital.

According to official data, the 24-hour average Air Quality Index (AQI) stood at 305 at 8 am on Friday, placing it firmly in the “very poor” category. This marked a sharp increase from the AQI of 234, recorded at 4 pm on Thursday, which was categorised as “poor”. The AQI had been 271 on Wednesday and had touched a “severe” level of 412 on Tuesday, highlighting the fluctuating pollution levels in the city over the past few days.

Experts attributed the brief improvement earlier this week to stronger winds, which reached speeds of up to 20 kilometres per hour and helped disperse pollutants. However, with wind speeds dipping again, the accumulated pollutants have led to a deterioration in air quality, underscoring Delhi’s vulnerability to even small changes in weather conditions during the winter months.

Meteorological officials said that the minimum temperature on Friday rose slightly to 7.7 degrees Celsius, compared to 6.5 degrees Celsius recorded on Thursday. Despite this marginal increase, the city continues to experience cold winter nights, with temperatures expected to remain in the range of 5 to 8 degrees Celsius until Monday.

The India Meteorological Department (IMD) has indicated that another western disturbance is likely to influence northwest India after Monday. This weather system is expected to bring changes in wind patterns and cloud cover, which may lead to a gradual rise in minimum temperatures in Delhi and adjoining regions.

However, before any significant relief arrives, residents may have to brace for dense to very dense fog, particularly during the early morning hours. Meteorologists warned that as wind speeds continue to dip, conditions will become favourable for fog formation, potentially affecting visibility and disrupting road, rail and air traffic.

The Early Warning System for Delhi (EWS), which provides forecasts on air quality trends, said that while the AQI was expected to improve slightly during the day on Friday due to sunny conditions, it was likely to deteriorate again later in the day. “Under sunny conditions, some improvement is expected during the daytime, but air quality is likely to return to the ‘very poor’ category by evening,” the EWS stated.

Looking ahead, the EWS forecast suggests that Delhi’s air quality will likely remain in the “poor” category until Saturday. However, it is expected to worsen again, slipping into the “very poor” category on Sunday and Monday. “The outlook for the subsequent six days from December 29 shows the air quality is likely to be in the ‘very poor’ category,” the forecast added.

These projections have raised concerns among health experts, who warn that prolonged exposure to “very poor” air quality can aggravate respiratory and cardiovascular conditions, particularly among children, the elderly and those with pre-existing health issues. Doctors advise people to limit outdoor activities, especially during early morning and late evening hours when pollution levels tend to be higher.

Delhi’s air pollution during winter is driven by a combination of local emissions and unfavourable meteorological conditions. Vehicular emissions, industrial pollution, dust, and the burning of biomass for heating contribute to the problem, while low wind speeds, temperature inversion and high moisture levels trap pollutants close to the ground.

Earlier this week, stronger winds brought temporary relief, helping the AQI improve from “severe” to “poor” levels. However, experts have long cautioned that such improvements are often short-lived unless sustained by favourable weather or long-term emission control measures.

Authorities have been closely monitoring air quality levels, especially in light of recent episodes when the AQI crossed into the “severe” category, prompting the implementation of restrictions under the Graded Response Action Plan (GRAP). While some curbs were eased during the brief improvement, officials have said that they are prepared to reimpose stricter measures if pollution levels worsen further.

Environmentalists say the recurring pattern of deterioration highlights the need for more permanent solutions to Delhi’s air pollution crisis. “Every winter, we see the same cycle — brief improvement due to wind or rain, followed by rapid deterioration once conditions become unfavourable again. This shows how dependent we are on weather rather than systemic changes,” said an environmental expert.

The anticipated western disturbance later next week could bring some relief by altering wind patterns and increasing moisture, potentially helping to disperse pollutants. However, it may also increase fog formation, which can further trap pollution during nighttime and early morning hours.

For residents, the return of “very poor” air quality means continued discomfort and health concerns. Many people reported irritation in the eyes and throat, along with breathing difficulties, as pollution levels rose again on Friday morning.

As the city heads into the final days of December, the outlook remains challenging. With air quality expected to remain in the “very poor” category for much of the coming week, authorities, health experts and citizens alike are once again grappling with the familiar winter struggle against toxic air.

While weather conditions may offer intermittent relief, experts stress that sustained improvement will require consistent enforcement of pollution control measures, reduced emissions, and coordinated efforts across states in the region. Until then, Delhi’s residents are likely to continue navigating days of fluctuating air quality, hoping for winds strong enough to clear the air — even if only temporarily.