The effect of local pollution and transport dust on near surface aerosol properties over a semi-arid station from ground and satellite observations

Abstract

Mineral dust, originating in arid regions, exerts substantial influence on air quality, health, and climate, ranking it among the most impactful aerosols. Its capacity to travel over great distances can significantly impact local air quality. In our study conducted for the year 2021, we made use of unprecedented, simultaneous in situ measurements to assess the total number, mass concentrations, and size distribution of near-surface aerosols at a semi-arid station. Furthermore, we conducted an in-depth examination of dust episodes, drawing upon evidence from in situ measurements of surface aerosol properties and meteorological records. The highest total number concentrations (230.1 ± 60.61 cm⁻³) were recorded during the winter season, attributed to a combination of factors including low temperatures, high relative humidity, stable wind conditions, and limited dispersion. Our findings reveal a noteworthy correlation: for every 1% increase in the equivalent black carbon mass fraction, the diurnal temperature range rises by 1.73 °C, with a noticeable impact of the weekend effect. During the dust episodes occurring on April 7–10 and June 16–30, we observed a significant increase (> twofold) in various surface parameters, such as number size distribution (NSD), total and coarse mode mass concentrations, effective radius, and scattering coefficient. Particularly striking was the enhancement in NSD during these dust episodes, consistently exceeding twofold for aerosols larger than 1.0 µm and reaching as high as tenfold for aerosols larger than 5.0 µm. In addition to our surface observations, satellite vertical profiles showed a prominent dust elevated layer situated between 2 and 4 km altitude during the dust episodes. These observations were well-aligned with in situ surface data and dust columnar mass flux obtained from re-analysis data. Re-analysis and model data further support our findings, indicating a long-range transport of aerosols from the Middle East and South Asia during the dust episodes.