The low-emission zone from transport (LEZ) in Sofia reduces air pollution, a new report by the Ecological Association “For the Earth“ shows.
It is based on its own measurements and analysis of data from various official sources. Despite its limited territorial scope and duration of only three months a year, there is a temporary over 10% drop in the concentrations of one of the important and problematic pollutants for Sofia - nitrogen dioxide (NO2). The decrease was recorded between December 2024 and February 2025, during the active operation of the measure, compared to the same period in the previous year. The possible positive effect on air quality in the city, however, will become a reality in full when the ZNE becomes year-round.
For the first time, a high-ranking representative of the Sofia Municipality announced during the event for the presentation of the report by “Za Zemiata” yesterday that it will be proposed that the effective period of operation of the zone in Sofia be extended to 7 months a year from the current 3 months. The decision depends on approval by the members of the Sofia Municipal Council.
Decrease in pollution, albeit temporary
The low-emission zone from transport in the capital in a limited three-month regime (December - February) and not particularly strict restrictions was officially introduced at the end of 2023. Real control over the vehicles subject to regulation occurred only last winter. December 2024 was the first month with functioning video surveillance for violators and de facto implementation of the measure, which is why the analysis focuses on this period.
„Za Zemiata” has been measuring nitrogen dioxide pollution at dozens of points in Sofia for years. For the needs of the analysis, measuring instruments were placed at locations within, along the borders and outside the scope of the Small Ring of the ZNE. The main source of NO2 in Sofia is internal combustion engines, as a number of independent studies have shown.
The results of the organization's measurements, verified by a leading Swiss laboratory in Europe, show that precisely in December 2024, the first effective month of the ZNE, we have a reduction in NO2 levels of about 22% compared to the previous month. For the points located in the Small Ring, it reaches almost 25%. This speaks to the connection between the reduction in traffic pollution and the implementation of the measure.
An analysis was conducted based on data from „Za Zemiata” and the official measuring stations of the ExEa and Sofia Municipality, which excludes seasonality and weather conditions as serious factors for the observed decrease in pollution.
We are moving towards a 7-month low-emission zone
„We can consider with a high degree of confidence that the effect of reducing NO2 for this period is a result of the introduced traffic restriction measure“, points out Ivaylo Popov - one of the authors of the report from „Za Zemiata”. He specifies that despite the reported decrease in pollution, nitrogen dioxide levels in Sofia are above the permissible legal annual average. This is expected, because emissions from road transport in the city are not only from December to February; traffic is intense throughout the year. The conclusion is that if we want to achieve lower levels of pollution, we must reduce the sources of this pollution throughout the year.
“We are observing a clear, albeit small, decline. This is the right direction for implementing the Low Emission Zone, but more efforts are needed. In addition to becoming year-round, the Low Emission Zone from Transport must expand its scope both as a territory and as affected vehicle categories. It is extremely important and accelerated to develop alternatives related to clean, shared and active mobility in the city”, adds Popov.
The Deputy Mayor for Ecology of Sofia - Nadezhda Bobcheva, who took part in the “For the Earth” event, confirmed that the Low Emission Zone is having an effect according to the municipality's data. For this reason, the municipal administration plans to propose an important change to the Low Emission Zone by the end of the month: the restrictions will apply for 7 months of the year - from 01.10 to 30.04. The idea is for the new regime to come into effect from October 2027.
Why is it urgent to act?
One of the reasons why the most logical option from the example of other countries - to make the zone year-round - is not being proposed is the lack of a political majority in the SOS for such a move. The low-emission zone has a social cost, but it is important to also consider the serious health benefits of such measures.
Air pollution with aerosols hazardous to health such as fine dust particles (PM10 and PM2.5) and nitrogen dioxide is a serious health problem for the residents of Sofia. The reference values recommended by the World Health Organization have been systematically exceeded over the years. “For the Earth” also measures a systematic exceedance of the legal norms of NO2, which is not reported by the two traffic stations of the official monitoring system, which are incorrectly located. Bulgaria is also expected to introduce stricter norms for the various key pollutants for atmospheric air in cities according to the requirements of the new EU Air Directive. Thus, the NO2 standards will become even stricter, with the average annual standard being halved: from 40 µg/m3 to 20 µg/m3.
The reasons for this, which we must address with adequate and timely measures, are complex: geographical and climatic features, overpopulation, underdeveloped infrastructure, an aging car fleet and at the same time a high percentage of motorization.
The effect of air pollution is a startling health and social problem, with children being among the most at risk.