After introducing an altered traffic regime on Slovenska cesta, the black carbon concentrations in this area have decreased by 58% in comparison with the urban background location.

Apart from the standard measurements, this year the City of Ljubljana started with the implementation of the above-standard black carbon measurements.

Black carbon measurements do not belong to the standard set of measurements in accordance with Directive 2008/50 EC, but are nevertheless of crucial importance, especially with regard to assessing air pollution. The advantage of these measurements is that they enable analyzing and distinguishing the impact of traffic emissions from other sources of pollution. Since the black carbon measuring tool (aethalometer) only measures primary particles emitted to air directly from exhaust gas, but not also secondary particles formed in the atmosphere due to pollution, such black carbon measurements can precisely establish the share of local pollution as well as the effect of individual measures – data not available if using standard PM10 particle measurements.

This is also a parameter that is far more closely connected to the effects of air pollution on human health.

This year's key measure with regard to sustainable mobility in Ljubljana was the introduction of an altered traffic regime on part of the Slovenska Cesta, therefore the black carbon measurements were carried out at these locations and in appropriate periods with an aim to assess the environmental impact of this measure. The black carbon measurements provide data on the basis of which we can conclude what portion of particles is emitted directly from vehicle exhaust and what portion from other sources (fire pits).

Measurements were performed between 26 August and 23 October 2013 at three locations:
- Post of Slovenia (Slovenska Cesta/Čopova Ulica) – area with an altered traffic regime;
- EMS (environmental measurement system) location (Tivolska Cesta/Vošnjakova Ulica) – area of increased traffic;
- ARSO (Slovenian Environment Agency) location (Vojkova Cesta) – urban background.

Measurements were done by the company Aerosol, which has an excellent reputation on a global scale. This year, working together with the Pipistrel Company and Matevž Lenarčič, we were also the first in the world to measure the black carbon concentrations on a journey around the globe.

What Did the Black Carbon Measurements Show?

After having implemented the new traffic regime on Slovenska cesta, the black carbon concentrations in this area have decreased by 58% in comparison with the urban background location.
Prior to implementing this measure, the highest concentrations were measured on Slovenska Cesta and the lowest on Vojkova Cesta, which is a part of the urban background. In the first week following the implementation of the new measure, concentrations did not decrease significantly, most probably due to the construction works, which took place during the traffic rearrangement, whereas after 30 September 2013, concentrations decreased significantly.

Conclusion:

• Altered traffic regime on Slovenska cesta significantly improved the quality of air in the city centre. At a measuring point on Slovenska Cesta, the black carbon concentration considered as a norm-concentration for an urban background (Vojkova Cesta; this eliminated the impact of weather phenomena, which are the same in the entire basin) decreased by 58%. This indicates a major decrease of primary air pollutants, which shows that radical measures do have the potential to drastically improve the state of environment.
•In spite of rearranging the traffic regime on Slovenska Cesta and consequently redirecting the traffic flows, no increase of black carbon concentration was observed on Vošnjakova Ulica (environmental measurement system). The value of these concentrations decreased also at this measurement point.
•Also the measurements of other pollutants at other locations (Vošnjakova/Tivolska crossroads, near the Drama theatre) showed improvements in comparison with the same time period last year.