Modeling study on the roles of the deposition and transport of PM2.5 in air quality changes over central-eastern China

The role of PM_2.5 (particles with aerodynamic diameters ≤ 2.5 µm) deposition in air quality changes over China remains unclear. By using the three-year (2013, 2015, and 2017) simulation results of the WRF/CUACE v1.0 model from a previous work (Zhang et al., 2021), a non-linear relationship between the deposition of PM_2.5 and anthropogenic emissions over central-eastern China in cold seasons as well as in different life stages of haze events was unraveled. PM_2.5 deposition is spatially distributed differently from PM_2.5 concentrations and anthropogenic emissions over China. The North China Plain (NCP) is typically characterized by higher anthropogenic emissions compared to southern China, such as the middle-low reaches of Yangtze River (MLYR), which includes parts of the Yangtze River Delta and the Midwest. However, PM_2.5 deposition in the NCP is significantly lower than that in the MLYR region, suggesting that in addition to meteorology and emissions, lower deposition is another important factor in the increase in haze levels. Regional transport of pollution in central-eastern China acts as a moderator of pollution levels in different regions, for example by bringing pollution from the NCP to the MLYR region in cold seasons. It was found that in typical haze events the deposition flux of PM_2.5 during the removal stages is substantially higher than that in accumulation stages, with most of the PM_2.5 being transported southward and deposited to the MLYR and Sichuan Basin region, corresponding to a latitude range of about 24°N-31°N.

Spring 2018 Asian Dust Events: Sources, Transportation, and Potential Biogeochemical Implications

The input of aeolian mineral dust to the oceans is regarded as the major source in supplying bioavailable iron for phytoplankton growth. Severe dust events swept over East Asia during the 26 March to the 4 April 2018, decreasing air quality to hazardous levels, with maximum PM10 mass concentrations above 3000 μg m−3 in northern China. Based on a comprehensive approach that combines multiple satellite measurements, ground observations, and model simulation, we revealed that two severe Asian dust events originating from the Taklimakan and Gobi deserts on 26 March and 1 April, were transported through northern China and the East/Japan Sea, to the North Pacific Ocean by westerly wind systems. Transportation pathways dominated by mineral dust aerosols were observed at altitudes of 2–7 km in the source regions, and then ascending to 3–10 km in the North Pacific Ocean, with relatively denser dust plumes within the second dust episode than there were during the first. Our results suggest that mineral dust emitted from the Taklimakan and Gobi deserts could increase ocean primary productivity in the North Pacific Ocean by up to ~50%, compared to average conditions. This emphasizes the potential importance of the deposition of Asian mineral dust over the North Pacific Ocean for enhancing the biological pump.

Active microorganisms thrive among extremely diverse communities in cloud water

Clouds are key components in Earth’s functioning. In addition of acting as obstacles to light radiations and chemical reactors, they are possible atmospheric oases for airborne microorganisms, providing water, nutrients and paths to the ground. Microbial activity was previously detected in clouds, but the microbial community that is active in situ remains unknown. Here, microbial communities in cloud water collected at puy de Dôme Mountain’s meteorological station (1465 m altitude, France) were fixed upon sampling and examined by high-throughput sequencing from DNA and RNA extracts, so as to identify active species among community members. Communities consisted of ~10³−10⁴ bacteria and archaea mL^-1 and ~10²−10³ eukaryote cells mL^-1. They appeared extremely rich, with more than 28 000 distinct species detected in bacteria and 2 600 in eukaryotes. Proteobacteria and Bacteroidetes largely dominated in bacteria, while eukaryotes were essentially distributed among Fungi, Stramenopiles and Alveolata. Within these complex communities, the active members of cloud microbiota were identified as Alpha- (Sphingomonadales, Rhodospirillales and Rhizobiales), Beta- (Burkholderiales) and Gamma-Proteobacteria (Pseudomonadales). These groups of bacteria usually classified as epiphytic are probably the best candidates for interfering with abiotic chemical processes in clouds, and the most prone to successful aerial dispersion.

Competitive Adsorption of Acetic Acid and Water on Kaolinite

Mineral dust is prevalent in the atmosphere as a result of emissions from natural and anthropogenic sources. As mineral dust particles undergo long-distance transport, they are exposed to trace gases and water vapor. We have characterized the interactions of acetic acid on kaolinite using diffuse reflectance infrared Fourier transform spectroscopy and molecular modeling to determine the chemisorbed species present. After the addition of acetic acid, gas-phase water was introduced to explore how water vapor competes with acetic acid for surface sites. We found that four chemisorbed acetate species are present on kaolinite after exposure to acetic acid in which acetate bonds through a monodentate, bidenatate, or bidentate bridging linkage with an aluminum atom. These species exhibit varying levels of stability after the introduction of water, indicating that water vapor affects the adsorption of organic acids. These results indicate that the type of chemisorbed species determines its stability toward competitive adsorption, which has potential implications for atmospheric composition and ice nucleation.

Long range trans-Pacific transport and deposition of Asian dust aerosols

The deposition of Asian dust aerosols during their trans-Pacific transport might cause significant marine phytoplankton biomass increases. However, the knowledge of the trans-Pacific dust transport, deposition, and spatial distribution is still poor due to a lack of continuous and simultaneous observations in the Asian subcontinent, the north Pacific Ocean, and North America. The severe Asian dust storm during 6 to 9 April 2001 provided an opportunity to gain a better understanding of trans-Pacific dust transport and deposition, using a comprehensive set of observations from satellites, ground-based light detection and ranging, aircraft, and surface observation networks. The observations and model simulations outline the general pattern of dust transport, deposition, vertical profile, and spatial distribution. The following points were observed: (1) the surface dust concentrations decreased exponentially with the increasing dust transport distance from 80 degrees E to 120 degrees W along the transport pathway; (2) the altitude of the dust concentration peak increased with increasing transport distance in the north Pacific region; and (3) the spatial distribution of dust deposition mainly depended on the trans-Pacific transport route.