Effect of synoptic and dynamic weather conditions on sulfur odor episodes over Baghdad during cold months

Abstract

In recent years, during the colder months (January-February), Baghdad has occasionally been engulfed by a powerful sulfur-like odor that alarmed residents and kept many confined indoors with doors and windows shut, fearing potential health risks. To understand these episodes, hourly measurements from a ground-based monitoring station (AirLink station) at Mustansiriyah University were examined alongside reanalysis data from the CAMS global reanalysis (EAC4), which includes particulate matter, sulfur oxides, nitrogen compounds, black carbon, and organic aerosol. All these concentrations were determined with a horizontal resolution of 0.75º × 0.75º on 60 vertical levels, whereas atmospheric elements such as wind speed and direction and geopotential height obtained from ERA5 (the fifth generation ECMWF reanalysis) have vertical coverage from 1000 to 1 hPa, with global coverage and horizontal resolution of 0.25º × 0.25º. The analysis revealed that certain meteorological patterns—particularly low wind speeds, anticyclone high pressure, a shallow boundary layer, and moderate humidity—created favorable conditions for the buildup and persistence of pollutants, known as smog. Results show that the physical characteristics of atmospheric elements play a crucial role in constraining these phenomena. Although the emissions originated near Baghdad, rather than being constant, they likely came from local sources, including oil refineries south of the city, thermal power plants, and traditional brick kilns using sulfur-containing fuels. Overall, the findings highlight the decisive influence of wind speed and direction in driving these pollution events, linked to the presence of a high-pressure system over Iraq and the study area. The study’s output can forecast smog events on the time scales of days and hours.