Aditya Vaishya

Seasonal Variation of the Aerosol Light Scattering Coefficient in Marine Air of the Northeast Atlantic

Aerosol light scattering measurements were carried out using a TSI 3563 Nephelometer at the Mace Head Atmospheric Research Station, on the west coast of Ireland from year 2001–2010. A strong seasonal trend in the aerosol light scattering coefficient at 550 nm (σscat), for clean marine air masses, is observed with a high σscat value, [average (geometric mean)] of 35.3 Mm−1 (29.5 Mm−1), in January and a low σscat value of 13.7 Mm−1 (10.2 Mm−1), in July. This near threefold increase in the σscat value during the winter season is because of the large contribution of wind-speed generated sea-salt particles in the marine boundary layer. A high positive correlation coefficient of 0.82 was found between the percentage occurrence of relatively large Angstrom exponent (A) values (>1.2) and the percentage occurrence of lower σscat values (5–15 Mm−1) in the summer season. σscat and wind-speed have a high positive correlation coefficient of 0.88 whereas A and wind-speed have a negative correlation coefficient of −0.89. A values during the summer months indicate the dominance of sub-μm particles thus indicating the contribution of non-sea-salt sulphate and organics towards the σscat as these species show an enhanced concentration during the summer months.

Cleaner air: Brightening the pollution perspective?

Clean-air policies in developing countries have resulted in reduced levels of anthropogenic atmospheric aerosol pollution. Reductions in aerosol pollution is thought to result in a reduction in haze and cloud layers, leading to an increase in the amount of solar radiation reaching the surface, and ultimately, an increase in surface temperatures. There have been many studies illustrating coherent relationships between surface solar radiation and temperature however, a direct link between aerosol emissions, concentrations, and surface radiation has not been demonstrated to date. Here, we illustrate a coherence between the trends of reducing anthropogenic aerosol emissions and concentrations, at the interface between the North-East Atlantic and western-Europe, leading to a staggering increase in surface solar radiation of the order of ∼20% over the last decade.

Marine organics effect on sea-spray light scattering

Primary-produced sea-spray is typically composed of sea-salt, but in biologically-active regions, the spray can become enriched with organic matter which reduces hygroscopicity of sea-spray, thereby having a potential impact on aerosol scattering. This study shows that scattering enhancement of marine aerosol, as a function of increasing relative humidity, is reduced when enriched with organics whose results are used to develop a new hygroscopicity growth-factor parameterization for sea-spray enriched in organic matter. The parameterization reveals a dual state which flips from high-hygroscopicity and high-scattering enhancement to low-hygroscopicity and low-scattering enhancement as the organic volume fraction increases from below ∼ 0.55 to above ∼ 0.55. In terms of organic enrichment, the effect on Top of Atmosphere (TOA) direct radiative forcing (ΔF) is to reduce the cooling contribution of sea-spray by ∼ 5.5 times compared to pure sea-salt spray. The results presented here highlight a significant coup...

Aerosol light scattering dependency on wind speed in marine air

Aerosol light scattering measurements were carried out at the Global Atmosphere Watch (GAW) research station, Mace Head, on the west coast of Ireland. Analysis of ten years (2001-2010) of the aerosol light scattering coefficient (σscat) at 550nm reveals a strong seasonal trend with σscat values during the winter season being approximately three times that of the summer season. The σscat and the aerosol light backscattering coefficient (σbscat) for the winter (Low Biological Activity – LBA) and the summer (High Biological Activity-HBA) are dependent on the square of wind speed (U). Scattering properties for the LBA period are approximately twice those of the HBA period. 70% of the observed LBA-HBA scattering difference can be attributed to differences in refractive index alone, resulting from organicmatter enrichment during the HBA period.