Continuous long-term monitoring of black carbon (BC) mass concentration and aerosol light scattering coefficient (sigma(SCA)), supplemented by number size distribution and chemical composition, are utilized in this study to understand the temporal changes in aerosol properties, associated source processes and radiative effects at Ny-angstrom lesund (79 degrees N) in the Svalbard Archipelago. A statistically significant decreasing trend in BC (- 24.7 ng m(-3) decade(-1)) is observed during spring of 2010-2019. In contrast, sigma SCA depicted a general increasing trend (5.2 Mm(-1) decade(-1)) during 2011-2016. BC and sigma(SCA) were higher during winter and spring. Aerosol single scattering albedo was highest in May similar to 0.95 (during spring) and lowest in September similar to 0.87 (during summer). Fractional share of BC to total aerosol mass was higher in winter and summer. Anthropogenic SO42- and NO3- (after ssNa(+)) species dominated the summer, when total number and mass concentrations of aerosols were at their minimum. Elemental Carbon (EC) and Organic Carbon (OC) showed higher concentrations in spring with EC-to-OC ratio similar to 0.08 - 0.22. The columnar AOD varied between 0.01 and 0.20 (annual mean similar to 0.09), resulting in aerosol radiative forcing (in the top of the atmosphere) similar to 0.15 - 2.69 Wm(-2) in the month of April (during spring). Potential source contribution function (PSCF) revealed the dominant source areas to be over Europe and Russia in terms of contributing to the seasonal high BC mass concentrations at Ny-angstrom lesund. Our study has also revealed an unusual impact of biomass burning aerosols (advected from the Alaska wildfire) during July 2015.

Analysis of the climatology of aerosol properties is performed over Hanle (4500 m) and Merak (4310 m), two remote-background sites in the western trans-Himalayas, based on eleven years (2008-2018) of sun/sky radiometer (POM-01, Prede) measurements. The two sites present very similar atmospheric conditions and aerosol properties allowing us to examine them as continuous single-data series. The annual average aerosol optical depth at 500 nm (AOD(500)) is 0.04 +/- 0.03, associated with an Angstrom exponent (AE(440-870)) of 0.58 +/- 0.35 and a single scattering albedo (SSA(500)) of 0.95 +/- 0.05. AOD(500) exhibits higher values in May (similar to 0.07) and lower in winter (similar to 0.03), while AE(400-870) minimizes in spring, indicating influence by coarse-mode dust aerosols, either emitted regionally or long-range transported. The de-convolution of AOD(500) into fine and coarse modes justifies the aerosol seasonality and sources, while the marginal diurnal variation in all aerosol properties reveals a weak influence from local sources, except for some few aerosol episodes. The aerosol-volume size distribution presents a mode value at similar to 10 mu m with secondary peaks at accumulation (similar to 2 mu m) and fine modes (similar to 0.03 mu m) and low variability between the seasons. A classification of the aerosol types based on the fine-mode fraction (FMF) vs. SSA(500) relationship reveals the dominance of aerosols in the FMF range of 0.4-0.6, characterized as mixed (39%), followed by fine aerosols with high scattering efficiency (26%), while particles related to dust contribute similar to 21%, with low fractions of fine-absorbing aerosols (similar to 13%). The aerosol radiative forcing (ARF) estimates reveal a small cooling effect at the top of the atmosphere (-1.3 Wm(-2)), while at the surface, the ARF ranges from -2 Wm(-2) to -6 Wm(-2) on monthly basis. The monthly-mean atmospheric radiative forcing (similar to 1 to 4 Wm(-2)) leads to heating rates of 0.04 to 0.13 K day(-1). These ARF values are higher than the global averages and may cause climate implications over the trans-Himalayan region. (C) 2020 Elsevier B.V. All rights reserved.

Regular measurements of spectral Aerosol Optical Depth (AOD) at ten wavelengths, obtained from multi-wavelength radiometer (MWR) under cloudless conditions in the outskirts of the tropical urban region of Hyderabad, India for the period January 2008 to December 2009, are examined. In general, high AOD with a coarse-mode abundance is seen during the pre-monsoon (March to May) and summer monsoon (June to September) with flat AOD spectra and low angstrom ngstrom wavelength exponent (), while in post-monsoon (OctoberNovember) and winter (DecemberFebruary) seasons, fine-mode dominance and steep AOD spectra are the basic features. The aerosol columnar size distribution (CSD) retrieved from the spectral AOD using King's inversion showed bimodal size distributions for all the seasons, except for the monsoon, with an accumulation-mode radius at 0.120.25 mu m and a coarse-mode one at 0.861.30 mu m. On the other hand, the CSD during the monsoon follows the power law for fine mode and the unimodal distribution for coarse mode. The fine-mode aerosols during post-monsoon and winter appear to be associated with air masses from continental India, while the coarse-mode particles during pre-monsoon and monsoon with air masses originating from west Asia and western India. The single-scattering albedo (SSA) calculated using the OPAC model varied from 0.83 +/- 0.05 in winter to 0.91 +/- 0.01 during the monsoon, indicating significant absorption by aerosols due to larger black carbon mixing ratio in winter, whereas a significant contribution of sea-salt in the monsoon season leads to higher SSAs. Aerosol radiative forcing (ARF) calculated using SBDART shows pronounced monthly variability at the surface, top of atmosphere (TOA) and within the atmosphere due to large variations in AOD and SSA. In general, larger negative ARF values at the surface (65 to 80 W m2) and TOA (approximate to 17 W m2) are observed during the pre-monsoon and early monsoon, while the atmospheric heating is higher (approximate to 5070 W m2) during January-April resulting in heating rates of approximate to 1.62.0 K day1. Copyright (c) 2012 Royal Meteorological Society

Cairo is one of the largest megacities in the World and the particle load of its atmosphere is known to be particularly important. In this work we aim at assessing the temporal variability of the aerosol's characteristics and the magnitude of its impacts on the transfer of solar radiation. For this we use the level 2 quality assured products obtained by inversion of the instantaneous AERONET sunphotometer measurements performed in Cairo during the Cairo Aerosol CHaracterization Experiment (CACHE), which lasted from the end of October 2004 to the end of March 2006. The analysis of the temporal variation of the aerosol's optical depth (AOD) and spectral dependence suggests that the aerosol is generally a mixture of at least 3 main components differing in composition and size. This is confirmed by the detailed analysis of the monthly-averaged size distributions and associated optical properties (single scattering albedo and asymmetry parameter). The components of the aerosol are found to be 1) a highly absorbing background aerosol produced by daily activities (traffic, industry), 2) an additional, 'pollution' component produced by the burning of agricultural wastes in the Nile delta, and 3) a coarse desert dust component. In July, an enhancement of the accumulation mode is observed due to the atmospheric stability favoring its building up and possibly to secondary aerosols being produced by active photochemistry. More generally, the time variability of the aerosol's characteristics is due to the combined effects of meteorological factors and seasonal production processes. Because of the large values of the AOD achieved during the desert dust and biomass burning episodes, the instantaneous aerosol radiative forcing (RF) at both the top (TOA) and bottom (BOA) of the atmosphere is maximal during these events. For instance, during the desert dust storm of April 8, 2005 RFBOA. RFTOA, and the corresponding atmospheric heating rate peaked at -161.7W/m(2), -65.8 W/m(2), and 4.0 K/d, respectively. Outside these extreme events, the distributions of the radiative forcing values at BOA and TOA are Gaussian with means and standard deviations of 58 (27), and 19(11)W/m(2), respectively. These two negative values indicate a cooling effect at the 2 atmospheric levels but the largest absolute value at BOA corresponds to a trapping of solar radiation inside the atmosphere. The averages of the instantaneous forcing efficiencies (FE) derived from measurements performed at solar zenith angles between 50 and 76 are 195 (+/-42) and -62(+/-17)W/m(2).AOD(550) for BOA and TOA, respectively. The value at TOA is larger than in other urban environments, which could be due to the desert dust component backscattering more solar radiation to space than absorbing urban aerosols. The lower absorption of solar light by desert dust also explains qualitatively the lower than usual value of FEBOA. A more precise study of the effects of the desert dust and biomass burning aerosols shows that fluctuations of their monthly-averaged concentrations explain the departures of the TOA and BOA radiative forcings from the background situation. In April, the contributions of DD to the month averages of the instantaneous radiative forcing are as high as 53% at BOA, and 66% at TOA. In October, the biomass burning mode contributes 33 and 27% of these forcings, respectively. Noteworthy is that the contribution of DD to RF is never less than 17% (at BOA) and 27% (at TA), emphasizing the importance of the mineral dust component on the transfer of solar radiation above Cairo, and this even in months when no major dust storm is observed. (C) 2010 Elsevier B.V. All rights reserved.