The role of wintertime persistent inversion dynamics and drought conditions on PM10 concentrations in Istanbul, Türkiye.

Anthropogenic factors have intensified drought conditions, often transforming them into ecological disasters in many regions. Türkiye, located in the Mediterranean Basin, has experienced increasingly frequent and severe droughts, particularly affecting regions like Istanbul which is the focus of this study. This study investigates the impact of inversion levels and thickness during drought events on winter PM₁₀ concentrations in Kartal, Istanbul (northwestern Türkiye). For this purpose, winter PM₁₀ concentrations, wind speed (m/s) and wind direction data for the period 2008-2023, along with total precipitation (mm), minimum, average, and maximum temperature (°C) data for 1965-2023, were analyzed. The differing periods reflect PM₁₀ data availability from 2008 onward, while long-term meteorological data from 1965 provide a robust climatological baseline. Changes in PM₁₀ concentrations were analyzed using the drought indicator Standardized Precipitation-Evapotranspiration Index (SPEI)-1 monthly values, categorizing conditions as dry (SPEI < -0.99), normal (-0.99 < SPEI <0.99), and wet (SPEI >0.99). SPEI-1 was selected for its sensitivity to short-term drought variations and inclusion of evapotranspiration, unlike precipitation-only indices. Based on the winter precipitation anomalies and SPEI results, severe drought events were found in 2008, 2011, 2012, 2013, and 2014. During drought-affected winters, high-PM₁₀ concentration values (≥100 μg/m³) were observed when northeasterly light winds were active in the region (r = -0.92, p < 0.05). Furthermore, during the nighttime under winter drought conditions, when light northeasterly winds were dominant the inversion level was close to the surface (between 25 m and 130 m) and the inversion thickness was high (between 74 m and 484 m), severe PM₁₀ concentrations were observed. These conditions may facilitate dust transport from northern terrestrial areas to Kartal, Istanbul, while limiting dispersion which is a hypothesis requiring further validation.