The ground-based characteristics (optical and radiative properties) of dust aerosols measured during the springtime between 2001 and 2014 were investigated over urban Beijing, China. The seasonal averaged aerosol optical depth (AOD) during spring of 2001-2014 was about 0.78 at 440 nm. During dust days, higher AOD occurred associated with lower Ångström exponent (AE). The mean AE440-870 in the springtime was about 1.0, indicating dominance of fine particles over the region. The back-trajectory analysis revealed that the dust was transported from the deserts of Inner Mongolia and Mongolia arid regions to Beijing. The aerosol volume size distribution showed a bimodal distribution pattern, with its highest peak observed in coarse mode for all episodes (especially for dust days with increased volume concentration). The single scattering albedo (SSA) increased with wavelength on dust days, indicating the presence of more scattering particles. Furthermore, the complex parts (real and imaginary) of refractive index showed distinct characteristics with lower imaginary values (also scattering) on dust days. The shortwave (SW; 0.2-4.0 μm) and longwave (LW; 4-100 μm) aerosol radiative forcing (ARF) values were computed from the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model both at the top of atmosphere (TOA) and the bottom of atmosphere (BOA) during dust and non-dust (dust free) days, and the corresponding heating rates and forcing efficiencies were also estimated. The SW (LW) ARF, therefore, produced significant cooling (warming) effects at both the TOA and the BOA over Beijing.

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Abstract. Near-surface and vertical in situ measurements of atmospheric particles were conducted in Shanghai during 19-23 March 2010 to explore the transport and chemical evolution of dust particles in a super dust storm. An air quality model with optimized physical dust emission scheme and newly implemented dust chemistry was utilized to study the impact of dust chemistry on regional air quality. Two discontinuous dust periods were observed with one traveling over northern China (DS1) and the other passing over the coastal regions of eastern China (DS2). Stronger mixing extents between dust and anthropogenic emissions were found in DS2, reflected by the higher SO 2 / PM 10 and NO 2 / PM 10 ratios as well as typical pollution elemental species such as As, Cd, Pb, and Zn. As a result, the concentrations of SO ] ratio, suggesting the heterogeneous reactions between calcites and acid gases were significantly promoted in DS2 due to the higher level of relative humidity and gaseous pollution precursors. Lidar observation showed a columnar effect on the vertical structure of particle optical properties in DS1 that dust dominantly accounted for ∼ 80-90 % of the total particle extinction from near the ground to ∼ 700 m. In contrast, the dust plumes in DS2 were restrained within lower altitudes while the extinction from spherical particles exhibited a maximum at a high altitude of ∼ 800 m. The model simulation reproduced relatively consistent results with observations that strong impacts of dust heterogeneous reactions on secondary aerosol formation occurred in areas where the anthropogenic emissions were intensive. Compared to the sulfate simulation, the nitrate formation on dust is suggested to be improved in the future modeling efforts.

Lake Tahoe is an oligotrophic lake appreciated for its transparent waters, yet the Lake's clarity has been declining for several decades due in part to eutrophication. At the same time, a shift from nitrogen (N) toward phosphorus (P) limitation of phytoplankton has occurred that could be due to atmospheric deposition of nutrients with high N:P ratios. Atmospheric particle samples collected during 2005–2006 had a mean soluble N:P ratio of 192:1, well above the Redfield ratio of 16:1 typically required by phytoplankton. Samples collected during the Angora Fire that occurred in 2007 were particularly enriched in N relative to P, with a mean ratio >2800:1. A bioassay incubation experiment was conducted using locally collected atmospheric total suspended particulate (TSP) matter. TSP samples with high ammonium (NH4+) and low P content favored the growth of picoplankton (cells <3 µm) and opportunistic filamentous cyanobacteria, whereas larger nanophytoplankton (cells 3–20 µm) were better competitors when more P was available. Picoplankton growth can increase primary productivity without causing a large increase in chlorophyll (chl a) or biomass. Aerosol‐nutrient‐induced picoplankton growth (together with shifts in grazing dynamics and stratification trends) may contribute to the uncoupling between primary productivity, chl a, and biomass that has been observed in Lake Tahoe in the last several decades and, in particular, following the Wheeler and Angora Fires. The chemical composition of aerosols has a marked impact on ecosystem dynamics in Lake Tahoe with potential consequences to lake productivity and microbial community dynamics.