This study investigates the annual cycle of particulate matter (PM) concentrations in Krakow, Poland, using a dense grid of low-cost sensors (LCS) to analyze over one million unique records of PM, temperature, humidity, pressure, and wind speed observations. The research reveals two main PM seasons—warm and cold—rather than the traditional four seasons, highlighting the importance of high-resolution time and space data for sustainable urban planning. The findings show that air pollution sources are influenced by coal burning for heating in cold periods and agricultural land burning in warm periods. The study also demonstrates the impact of meteorological factors, particularly temperature, on PM concentrations, with a significant correlation observed during winter, fall, and spring. The analysis of regional patterns reveals that high-pollution areas are relatively stable in the cold months, along the southwest and northeast axes, and are influenced by morphological barriers. The research underscores the need for further studies and measures to reduce air pollution in urban areas.This study investigates the annual cycle of particulate matter (PM) concentrations in Krakow, Poland, using a dense grid of low-cost sensors (LCS) to analyze over one million unique records of PM, temperature, humidity, pressure, and wind speed observations. The research reveals two main PM seasons—warm and cold—rather than the traditional four seasons, highlighting the importance of high-resolution time and space data for sustainable urban planning. The findings show that air pollution sources are influenced by coal burning for heating in cold periods and agricultural land burning in warm periods. The study also demonstrates the impact of meteorological factors, particularly temperature, on PM concentrations, with a significant correlation observed during winter, fall, and spring. The analysis of regional patterns reveals that high-pollution areas are relatively stable in the cold months, along the southwest and northeast axes, and are influenced by morphological barriers. The research underscores the need for further studies and measures to reduce air pollution in urban areas.