The role of meteorological variables and cloud base heights in urban air quality

Air pollution stands out as a major problem that threatens the environment and public health in urban environmets. In a densely populated megacity like İstanbul, the concentration and distribution of pollutants are greatly affected by meteorological conditions and local environmental factors. In this study, hourly air quality data (PM₁₀, PM_2.5, NO, NO₂, NO_x, SO₂ and O₃), meteorological variables (temperature, relative humidity, wind speed and direction) and cloud base height (CBH) data measured with a ceilometer were analyzed between January 1, 2023 and December 31, 2023 in İstanbul. Pearson correlation coefficient, Mann-Kendall trend test and time series analysis methods were used to evaluate the data. The findings revealed seasonal variations in air pollutant levels and reach high concentrations in the winter months. It was determined that particulate pollutants such as PM₁₀ and PM_2.5 tend to accumulate especially in low temperature and high relative humidity (RH) conditions. A positive correlation was observed between RH and particulate pollutants, and a negative relationship with temperature and wind speed. For example, it was observed that particulate matter (PM) concentrations increased when the temperature decreased, and dispersion was facilitated during periods when wind speed was high. In addition, a strong relationship was found between CBH and air pollutants. Analyses showed that PM and gaseous pollutants tended to accumulate in the atmosphere during periods when CBH was low. This situation, combined with the decrease in atmospheric stability and the effect of high RH in winter months, further deteriorated air quality. Seasonal analyses showed that meteorological variables such as temperature, RH and wind had varying impacts on on air quality. In particular, it was determined that gaseous pollutants such as NO_x and SO₂ increased during winter months, and this was associated with low atmospheric mixing and high stability conditions. Additionally, winds originating from certain directions were found to contribute to elevated pollutant concentrations.