Analysis of the relationship between dust aerosol and precipitation in spring over East Asia using EOF and SVD methods

This study utilized the Empirical Orthogonal Function (EOF) and Singular Value Decomposition (SVD) methods to investigate the spatial and temporal patterns and trends of dust aerosol and precipitation, and to identify the coupled modes between them. The research employed MODIS and CALIPSO retrieved dust aerosol optical depth (DAOD) data to represent dust aerosol information and CMORPH data to provide precipitation information. The results indicated that specific dust source regions were associated with the primary modes of spring dust in East Asia, while atmospheric circulation and land-sea monsoon were closely related to the primary modes of spring precipitation. Additionally, the study revealed that the impact of dust aerosol on precipitation varied based on the source region within the coupled modes. The first coupled mode, with dust sources in the Mongolian Gobi and Taklamakan Desert, demonstrated a pattern of increased dust aerosol and reduced precipitation in most regions. The second coupled mode, with dust sources focused on the Mongolian Gobi, exhibited a consistent pattern of increased dust aerosol and a significant increase in precipitation in northern China. This study highlights the significance of considering dust source regions when examining the relationship between dust aerosol and precipitation, providing new insights into the potential impact of dust aerosol on precipitation in East Asia during the spring.

Heterogeneous photochemistry of oxalic acid on Mauritanian sand and Icelandic volcanic ash

Teragram quantities of crustal and volcanic aerosol are released into the atmosphere on an annual basis. Although these substrates contain photoactive metal oxides, little is known about the role that they may play in catalyzing the heterogeneous phototransformation of semivolatile organic species. In the present study, we have investigated oxalic acid photochemistry at the surface of Fe(2)O(3), TiO(2), Mauritanian sand, and Icelandic volcanic ash in the presence and absence of oxygen using a photochemical Knudsen cell reactor. Illumination of all sample types resulted in the production of gas-phase CO(2). In the case of Mauritanian sand, the production of gas-phase CO(2) scaled with the loss of surface oxalic acid. In the absence of oxygen, the production of CO(2) by the sand and ash films scaled with the absorption spectrum of iron oxalate, which suggests that the reaction is at least in part iron-mediated. The presence of oxygen suppressed CO(2) production at the Fe(2)O(3) surface, enhanced CO(2) production at the Mauritanian sand surface, and did not have a net effect upon CO(2) production at the Icelandic ash surface. These different oxygen dependencies imply that oxalic acid photochemistry at the authentic surfaces under study was not solely iron-mediated. Experiments at the TiO(2) surface, which showed enhanced CO(2) production from oxalic acid in the presence of oxygen, suggest that Ti-mediated photochemistry played an important role. In summary, these results provide evidence that solid-phase aerosol photochemistry may influence the atmospheric lifetime of oxalic acid in arid regions, where its removal via wet deposition is insignificant.