Comparison of MERRA-2 black carbon aerosols and ground observation at a high-altitude mountainous site in southern China

Abstract

Black carbon (BC) is an important light-absorbing component of atmospheric aerosols and plays a crucial role in regional/global climate and human health. In contrast to the predominant focus on urban BC aerosols in existing literature, this study comprehensively compared and studied the temporal variations of BC concentration at a high-altitude mountainous site (Mt. Lushan) in southern China based on long-term (2008–2022) ground observations and elevation-corrected MERRA-2 reanalysis. Results indicate that both the observed and MERRA-2 annual mean BC concentrations show a downward trend over the years. However, the observed decline rate (−0.115 μg m⁻³ yr⁻¹) is considerably larger than that of MERRA-2 (−0.045 μg m⁻³ yr⁻¹), mainly attributed to MERRA-2's static emission inventory after 2013. Both datasets capture a “V-shaped” monthly variation pattern, but MERRA-2 overestimates winter BC by 68 % and underestimates summer BC by 8 %. Despite notable discrepancies during winter and at night, the diurnal variations of MERRA-2 and observed BC exhibit a consistent unimodal distribution, with its peak occurring between 12:00 and 17:00 local standard time (LST). This pattern contrasts with those observed in urban areas. A comparison reveals that using ground-level MERRA-2 reanalysis against the observation at Mt. Lushan results in larger biases than that using station elevation-matched product. This suggests that station elevation plays a significant role in the temporal variation of BC concentration, and it is preferable to use model-level BC data from MERRA-2 that corresponds to the actual station altitude for comparison at such high-altitude sites. These results could provide a referenced evaluation and promote the understanding on the applicability and accuracy of the MERRA-2 BC variation pattern over high-altitude sites.