Nonlinear enhancement of radiative absorption by black carbon in response to particle mixing structure

Abstract. A continuous measurement for black carbon conducted on a shallow ice core extracted from the East Rongbuk glacier beside Mt. Qomolangma recovers the first historical record of black carbon 13 deposition in the past ~50 years in the high Asian cryosphere. Fast increasing trend of BC concentration is revealed since the mid-1990s. Backward air trajectory analysis indicates that South Asia's emission has significant impacts on the BC deposition in the East Rongbuk glacier. The estimated atmospheric BC concentration over the East Rongbuk glacier is about 80 ngC m−3. This suggests black carbon from South Asia's emission might penetrate into the Tibetan Plateau by 18 climbing over the elevated Himalayas. Considering the consequent extra solar radiative absorption over the glacier, it is suggested that this amplitude of BC concentration in the atmosphere over the Himalayas could not be neglected when assessing the warming effect on the surface of the glaciers on the Himalayas.

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The filter loading effect by ambient aerosols in filter absorption photometers depends on the mixing state of the sampled particles

10.5194/amt-2016-285 ◽

2016 ◽

Author(s):

Luka Drinovec ◽

Asta Gregorič ◽

Peter Zotter ◽

Robert Wolf ◽

Emily Anne Bruns ◽

...

Keyword(s):

Black Carbon ◽

Carbon Particle ◽

Mixing State ◽

Ambient Aerosols ◽

Loading Effect ◽

Particle Mixing ◽

Filter Loading ◽

Ångström Exponent ◽

Loading Parameter ◽

Black Carbon Particle

Abstract. Black carbon is a primary aerosol tracer for high-temperature combustion emissions and can be used to characterize the time evolution of its sources. It is correlated with a decrease in public health and contributes to atmospheric warming. Black carbon measurements are usually conducted with absorption filter photometers, which are prone to the filter-loading effect – a saturation of the instrumental response due to the accumulation of the sample in the filter matrix. In this paper, we investigate the hypothesis that this filter-loading effect depends on the optical properties of particles present in the filter matrix, especially on the black carbon particle mixing state. We conducted field campaigns in contrasting environments to determine the influence of source characteristics, particle age and coating on the magnitude of the filter-loading effect. High time resolution measurements of the filter-loading parameter in filter absorption photometers show daily and seasonal variations of the effect. The variation is most pronounced in the near-infrared region, where the black carbon mass concentration is determined. During winter, the filter-loading parameter value increases with the absorption Ångström exponent. It is suggested that this effect is related to the size of the black carbon particle core as the wood burning (with higher values of the absorption Ångström exponent) produces soot particles with larger diameters. A reduction of the filter-loading effect is correlated with the availability of the coating material. As the coating of ambient aerosols is reduced or removed, the filter-loading parameter increases. Coatings composed of ammonium sulfate and secondary organics seem to be responsible for the variation of the loading effect. The potential source contribution function analysis shows that high values of the filter-loading parameter in the infrared are indicative of local pollution, whereas low values of the filter-loading parameter result from ageing and coating during long range transport. Our results show that the filter-loading parameter can be used as proxy for determination of the particle mixing state, thus allowing for differentiation between local/fresh and transported/aged particles.

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