The effect of decreased mobility on air quality due to the COVID-19 period was analysed from 2018 to 2022 in Debrecen city, Hungary. The PM₁₀ concentrations were analysed at three sampling sites. We compared PM₁₀ concentrations from 2018 to 2022 during three periods: pre-pandemic, pandemic, and post-pandemic. We also studied the effect of lockdowns on the PM₁₀ concentrations during the pandemic period. Over the 2018–2022 period, the concentration of PM₁₀ decreased across all sites, suggesting improved air quality. Significant differences were found in PM₁₀ levels among the pre-pandemic (before February of 2020), pandemic (from March of 2020 to February 2022), and post-pandemic period (after March of 2022) in the case of all stations. Significant differences were also found among years and stations during the lockdown periods. Drastically significant decreases were found only in January of 2021 in the case of all stations. Our results also demonstrated that the reduction in emissions took place simultaneously, as exceptional weather conditions such as wind direction and wind speed were observed in the year 2020, which have been highlighted by an unusually warm pre-lockdown February and springtime drought. PM₁₀ levels indicated heterogeneous patterns characterized by variations including decreases, slight increases, or stability, contingent upon the specific sampling sites under consideration. These findings emphasize the complex dynamics of air pollutants and stress the necessity for ongoing monitoring and targeted interventions to alleviate detrimental effects on air quality and public health.

This study focused on the spatial and temporal changes in photosynthetic pigment concentrations in the leaves of Ginkgo biloba and their integration into a new bioindicator index, the Pigment Integrity-to-Dust Ratio (PIDR), to assess urban air pollution stress on trees in Budapest, Hungary. High levels of chlorophyll and carotenoids in early summer indicated greater pigment integrity at the moderate-traffic site, whereas there were clear indications of reductions in the high-traffic area. The control site represented a low-traffic, pollution-free baseline. Chlorophyll concentrations dropped in the traffic-exposed leaves, and there were increased levels in the formation of pheophytin. It is thought that these reductions were caused by city stress. Responses of pigments were also variable at the moderate site, perhaps due to some form of recovery or adjustment in the study’s time frame. The observed negative relationships between selected pollutants and PIDR suggested that pollutant exposure was associated with pigment degradation and foliar dust deposition, although these associations should be interpreted as exploratory. The Air Pollution Tolerance Index (APTI) was significantly different between the pollution-exposed sites and the control, reflecting physiological tolerance in chronically exposed trees rather than directly measuring pigment damage. Therefore, the APTI and PIDR provide complementary information. Overall, the PIDR appears to be a promising exploratory bioindicator of physiological stress response, based on pigment concentration changes and dust deposition.