The characteristics of carbonaceous aerosol in Beijing during a season of transition

Interdecadal variation in aerosol optical properties and their relationships to meteorological parameters over northeast China from 1980 to 2017

Northeast China has undergone rapid urbanisation with increased anthropogenic emissions, and the types and absorption properties of aerosols may affect regional climate change. MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2) distributions of aerosol optical depth (AOD), Ångström exponent (AE), and absorption aerosol optical depth (AAOD) from 1980 to 2017 was studied to estimate the climatology of aerosol optical properties over Northeast China. The highest AOD and AAOD occurred in Liaoning Province range from 0.3 to 0.4 and 0.02-0.03, respectively. The spacial distribution of black carbon (BC) AOD was similar to AAOD with maximum value in Liaoning province about 0.04 related to the emission sources and human activities. The seasonal interdecadal distribution indicated larger dust (DU) AOD in Liaoning (0.12) and organic carbon (OC) AOD in Heilongjiang (0.18). The contribution of SO₄ to total AOD was significant in autumn and winter, and BC particles contributed 70% to total AAOD in all seasons. The decadal change in AOD was positive for 2000-2009 (0.2/decadal) due to the increased dust events happening in spring. The positive correlation between AOD and relative humidity (RH) at surface was about 0.4-0.6; the negative correlation between AOD and surface wind speed (WS) (-0.6), planetary boundary layer height (PBLH) (-0.2 to -0.6), sea level pressure (SLP) (-0.2) was found over the study period. This study's findings enable more comprehensive understanding of the distribution of aerosols optical properties and regional climatology in Northeast China.

Insights into the origin and evolution of carbonaceous aerosols in a mediterranean urban environment

Organic carbon (OC) and elemental carbon (EC) concentrations were measured in PM₁ and PM₁₀ daily samples collected at an urban station in Elche (southeastern Spain) from February 2015 to February 2018. The effect of seasonal weather conditions, traffic, and specific pollution events (Saharan dust outbreaks and local pollution episodes) on the variability of carbonaceous aerosol levels was studied in this work. The joint contribution of carbonaceous species to PM₁ and PM₁₀ mass concentrations was, respectively, 48% and 26%. Both OC and EC concentrations were higher in winter than in summer because of the poor dispersion conditions and lower temperatures leading to the condensation of semivolatile species. Secondary organic carbon (SOC), estimated using the EC tracer method, also exhibited higher concentrations during winter, indicating that the prevailing meteorological conditions during the cold season are more favorable for the formation of secondary organic aerosols. Our results suggest different formation pathways of secondary organic components during summer and winter. At the sampling site, EC was primarily derived from traffic emissions, independently of the season and the type of event, with a modest contribution from biomass burning (<20%). The estimated contribution from this source to OC levels was similar. Local pollution episodes lead to a significant increase in the concentrations of carbonaceous species, in particular of SOC, influencing its temporal variation. On average, African dust outbreaks showed a moderate impact on the levels of carbonaceous aerosols; however, the effect was significantly stronger during winter Saharan events.