Mobile air quality measurement campaign in Zagreb, Croatia - black carbon and particles

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The mobile monitoring campaign was conducted in the City of Zagreb during the summer of 2026, from July 26 to August 4. The main field measurements were carried out over seven consecutive days, from July 29 to August 4, 2026, with two test runs on July 26 and 28. The summer period was deliberately selected to minimise the contribution of seasonal black carbon (BC) sources, such as biomass combustion and residential heating. Consequently, the measured pollutant concentrations can be attributed more reliably to traffic emissions as the dominant local source. We drove the selected route by car and repeated it during both morning and evening periods throughout the seven-day measurement campaign. Each individual run lasted approximately 2 h. To capture a broader range of temporal variation in pollutant concentrations, we varied the start time of each run across days. In addition, we randomly alternated the direction of travel along the route. We used a Naneos Particle 2 Pro multimetric aerosol detector to measure ultrafine particle-related metrics, and an AethLabs MA200 aethalometer to measure black carbon mass concentration. We selected both instruments for their compact size and portability, which are essential for a mobile monitoring campaign. The MA200 aethalometer was operated with a flow rate of 150 mL/min, time base of 1 s, the tape-advance attenuation (ATN) threshold set at 50 and in SingleSpot mode. The Partector 2 Pro was operated at a sample flow rate of 500 mL/min with a time base of 2 s. Because of the sensor's internal operating procedure, data were recorded at 4 s intervals.Prior to each measurement run, the instruments were allowed to warm up for at least 30 min. Due to high summer air temperatures and the instrument's maximum operating temperature limit of 40 °C, the sensors could not be mounted outside the vehicle. Instead, both instruments were placed inside the vehicle, while ambient air was sampled through two separate PVC tubes extending from the exterior of the vehicle to each instrument. The PVC tube has an inner diameter of 6 mm and a total length of 1m. The sampling inlet was positioned at approximately 1.56 m above ground level on the roof of the vehicle and as far from the vehicle exhaust outlet to minimise potential self-sampling of the vehicle’s own exhaust emissions. To minimise the influence of humidity on the measurements, custom 3D-printed drying units containing silica gel were used to dry the sampled air. This precaution was particularly important for the aethalometer measurements, as condensation or evaporation of water on the filter and/or optical components can alter light attenuation. The instrument may then incorrectly interpret this change in optical signal as a change in black carbon concentration. Because the instruments were placed inside an air-conditioned vehicle and a dryer was used, temperature and humidity data are not representative of the actual meteorological conditions of the outdoor ambient air. (Cameras were set up on the front and back of the car to record its surroundings. The footage was used to get a count of the number of cars in the vicinity of the sampling inlet.) Data validation was conducted on August 3 2026, from 12:10 to 13:15, during a collocation experiment in which the sampling inlets of the MA200 and Partector 2 Pro were positioned immediately adjacent to those of an AE33 aethalometer and a Scanning Mobility Particle Sizer (SMPS), which served as reference instruments. The reference data were provided by by Ruđer Bošković Institute. The Croatian Meteorological and Hydrological Service provided meteorological data for the City of Zagreb for the measurement period.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.