Information
about how fine particulate matter (PM2.5) concentrations
vary over the course of a day on a global scale
is limited. We used aggregated data sources to analyze the diurnal
cycle of PM2.5 from more than 17 million hourly measurements
at 3110 sites across the world, primarily in North America, Europe,
and East Asia. The measurements reveal that diurnal PM2.5 cycles exhibit similar patterns across sites worldwide with a mean
diurnal variability of 13.1%. PM2.5 cycles have a morning
peak between 7:00 and 10:00 local solar time (LST) and an early nighttime
peak between 21:00 and 23:00 LST, with an afternoon minimum occurring
between 15:00 and 17:00 LST. Diurnal cycles are associated with dynamics
of the atmospheric mixed layer as well as diurnal emission patterns,
exhibiting an increased amplitude in regions with a large mixed layer
height and mountainous terrain.
Abstract. Observations of aerosol scattering and absorption offer valuable information about aerosol composition. We apply a simulation of the Ultraviolet Aerosol Index (UVAI), a method of detecting aerosol absorption from satellite observations, to interpret UVAI values observed by the Ozone Monitoring Instrument (OMI) from 2005 to 2015 to understand global trends in aerosol composition. We conduct our simulation using the vector radiative transfer model VLI-DORT with aerosol fields from the global chemical transport model GEOS-Chem. We examine the 2005-2015 trends in individual aerosol species from GEOS-Chem and apply these trends to the UVAI simulation to calculate the change in simulated UVAI due to the trends in individual aerosol species. We find that global trends in the UVAI are largely explained by trends in absorption by mineral dust, absorption by brown carbon, and scattering by secondary inorganic aerosol. Trends in absorption by mineral dust dominate the simulated UVAI trends over North Africa, the Middle East, East Asia, and Australia. The UVAI simulation resolves observed negative UVAI trends well over Australia, but underestimates positive UVAI trends over North Africa and Central Asia near the Aral Sea and underestimates negative UVAI trends over East Asia. We find evidence of an increasing dust source from the desiccating Aral Sea that may not be well represented by the current generation of models. Trends in absorption by brown carbon dominate the simulated UVAI trends over biomass burning regions. The UVAI simulation reproduces observed negative trends over central South America and West Africa, but underestimates observed UVAI trends over boreal forests. Trends in scattering by secondary inorganic aerosol dominate the simulated UVAI trends over the eastern United States and eastern India. The UVAI simulation slightly overestimates the observed positive UVAI trends over the eastern United States and underestimates the observed negative UVAI trends over India. Quantitative simulation of the OMI UVAI offers new insight into global trends in aerosol composition.
The size of crystal grains in lead halide perovskite thin films remains a vital design feature for durable optoelectronic devices. With larger crystals and reduced grain boundaries per surface area, the stability of the structures improves as degradation, caused by moisture and oxygen percolating into the grain boundaries, is minimized. Thus far, large scale continuous lateral films of methylammonium lead iodide (MAPbI 3 ) with macroscale crystal grains compatible with thin film (<1 μm thick) solar cells and photodetectors have not been reported. Herein, we employ meniscus-guided blade coating technique to grow thin films of highly oriented millimeter-size MAPbI 3 crystals, resulting in over an order of magnitude responsivity enhancement over spin-coated films in lateral photoconductors with channel lengths over 100 μm. Furthermore, the blade-coated MAPbI 3 thin films exhibit anisotropic higher conductivity along crystal grains over a millimeter range. With crystals orders of magnitude larger in size, and with no additive treatment or additional layers, blade-coated devices manifest improved stability and retain over 80% of their performance tested in ambient air for over 300 h in comparison to spin-coated devices that reach less than 50% of their original peformance within the first 36 h.
diameter rotary-pullback fiber-optic endoscope for narrowband red-green-blue reflectance, optical coherence tomography, and autofluorescence in vivo imaging,"
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