Abstract: It is well known that the aerosol distribution in Asia is complex due to both the increasing emissions of the anthropogenic aerosols associated with economic growth and the behavior of natural dusts. Therefore, detailed observations of atmospheric particles in Asian urban cities are important. In this work, we focus on the spatial and temporal variations of atmospheric particles around Higashi-Osaka in Japan. Higashi-Osaka is located in the eastern part of Osaka, the second-largest city in Japan, and is famous for small- and medium-sized manufacturing enterprises. For this study, we placed various ground measurement devices around the Higashi-Osaka campus of Kinki University including a Cimel sunphotometer supported by NASA/AERONET (Aerosol robotics network), suspended particulate matter (SPM) sampler and LIDAR (light detection and ranging). Individual particle analyses with a SEM (scanning electron microscope)/EDX (energy-dispersive X-ray analyzer) show the temporal variations of particle properties, such as size, shape and components, during a dust event on 21 March 2010. The simultaneous measurement using a portable sun photometer with AERONET was conducted from April to November 2011. A comparison of the data at each site and the combination of the observed LIDAR data and model simulations indicate the difference in the transportation processes between dust and anthropogenic particles. We suppose this difference is attributed to the differences in the vertical aerosol profiles, where one aerosol is transported over Mount Ikoma and the other is blocked by it.

Abstract: This paper reviews the current state and development of different numerical model classes that are used to simulate the global atmospheric system, particularly Earth’s climate and climate-chemistry connections. The focus is on Chemistry-Climate Models. In general, these serve to examine dynamical and chemical processes in the Earth atmosphere, their feedback, and interaction with climate. Such models have been established as helpful tools in addition to analyses of observational data. Definitions of the global model classes are given and their capabilities as well as weaknesses are discussed. Examples of scientific studies indicate how numerical exercises contribute to an improved understanding of atmospheric behavior. There, the focus is on synergistic investigations combining observations and model results. The possible future developments and challenges are presented, not only from the scientific point of view but also regarding the computer technology and respective consequences for numerical modeling of atmospheric processes. In the future, a stronger cross-linkage of subject-specific scientists is necessary, to tackle the looming challenges. It should link the specialist discipline and applied computer science.

Abstract: Wet deposition of mercury (Hg) across the United States is influenced by changes in atmospheric conditions, domestic emissions and global background emissions. We examine trends in Hg precipitation concentrations at 47 Mercury Deposition Network (MDN) sites during 2004–2010 by using the GEOS-Chem nested-grid Hg simulation. We run the model with constant anthropogenic emissions and subtract the model results from the observations. This helps to remove the variability in observed Hg concentrations caused by meteorological factors, including precipitation. We find significant decreasing trends in Hg concentrations in precipitation at MDN sites in the Northeast (−4.1 ± 0.49% yr⁻¹) and Midwest (−2.7 ± 0.68% y^r−1). Over the Southeast (−0.53 ± 0.59% yr⁻¹), trends are weaker and not significant, while over the West, trends are highly variable. We conduct model simulations assuming a 45% decrease in Hg emissions from domestic sources in the modeled period and a uniform 12% decrease in background atmospheric Hg concentrations. The combination of domestic emission reductions and decreasing background concentrations explains the observed trends over the Northeast and Midwest, with domestic emission reductions accounting for 58–46% of the decreasing trends. Over the Southeast, we overestimate the observed decreasing trend, indicating potential issues with our assumption of uniformly decreasing background Hg concentrations.

Abstract: Six meteorological drought indices including percent of normal (PN), standardized precipitation index (SPI), China-Z index (CZI), modified CZI (MCZI), Z-Score (Z), the aridity index of E. de Martonne (I) are compared and evaluated for assessing spatio-temporal dynamics of droughts in six climatic regions in Iran. Results indicated that by consideration of the advantages and disadvantages of the mentioned drought predictors in Iran, the Z-Score, CZI and MCZI could be used as a good meteorological drought predictor. Depending on the month, the length of drought and climatic conditions of the region, they are an alternative to the SPI that has limitations both because of only a few available long term data series in Iran and its complex structure.

Abstract: This study examines the characteristics of new particle formation at a forest site in southeastern US. Particle size distributions above a Loblolly pine plantation were measured between November 2005 and September 2007 and analyzed by event type and frequency, as well as in relation to meteorological and atmospheric chemical conditions. Nucleation events occurred on 69% of classifiable observation days. Nucleation frequency was highest in spring. The highest daily nucleation (class A and B events) frequency (81%) was observed in April. The average total particle number concentration on nucleation days was 8,684 cm⁻³ (10 < D_p < 250 nm) and 3,991 cm⁻³ (10 < D_p < 25 nm) with a mode diameter of 28 nm with corresponding values on non-nucleation days of 2,143 cm⁻³, 655 cm⁻³, and 44.5 nm, respectively. The annual average growth rate during nucleation events was 2.7 ± 0.3 nm·h⁻¹. Higher growth rates were observed during summer months with highest rates observed in May (5.0 ± 3.6 nm·h⁻¹). Winter months were associated with lower growth rates, the lowest occurring in February (1.2 ± 2.2 nm·h⁻¹). Consistent with other studies, nucleation events were more likely to occur on days with higher radiative flux and lower relative humidity compared to non-nucleation days. The daily minimum in the condensation sink, which typically occurred 2 to 3 h after sunrise, was a good indicator of the timing of nucleation onset. The intensity of the event, indicated by the total particle number concentration, was well correlated with photo-synthetically active radiation, used here as a surrogate for total global radiation, and relative humidity. Even though the role of biogenic VOC in the initial nuclei formation is not understood from this study, the relationships with chemical precursors and secondary aerosol products associated with nucleation, coupled with diurnal boundary layer dynamics and seasonal meteorological patterns, suggest that H₂SO₄ and biogenic VOC play a role in nucleated particle growth at this site.

Abstract: This paper presents an approach using the GEneralized Nonlinear Retrieval Analysis (GENRA) tool and general inverse theory diagnostics including the maximum likelihood solution and the Shannon information content to investigate the performance of a new spectral technique for the retrieval of cloud optical properties from surface based transmittance measurements. The cumulative retrieval information over broad ranges in cloud optical thickness (τ), droplet effective radius (r_e), and overhead sun angles is quantified under two conditions known to impact transmitted radiation; the variability in land surface albedo and atmospheric water vapor content. Our conclusions are: (1) the retrieved cloud properties are more sensitive to the natural variability in land surface albedo than to water vapor content; (2) the new spectral technique is more accurate (but still imprecise) than a standard approach, in particular for τ between 5 and 60 and r_e less than approximately 20 μm; and (3) the retrieved cloud properties are dependent on sun angle for clouds of  from 5 to 10 and r_e < 10 μm, with maximum sensitivity obtained for an overhead sun.