MABCaM

Global efforts to mitigate climate change have largely focused on reducing emissions of carbon dioxide (CO2), which is responsible for 55-60% of current anthropogenic radiative forcing on warming impact. Because of its long lifetime (~ 130 years [Sonnemann 2013]) in the atmosphere, long-lasting CO2 will remain the primary driver of long-term temperature rise even if new CO2 emissions dropped to zero. A "fast-action" climate mitigation strategies is therefore strongly needed to provide more sizeable short-term benefits than CO2 reductions by reducing emission of short-lived climate pollutants (SLCPs) having atmospheric lifetimes of less than 20 years [Zaelke 2013], which would lead to short-term drops in atmospheric concentrations and hence slow climate change over the next several decades. Black carbon (BC), one of the most important SLCPs with an atmospheric lifetime of about one week, warms the atmosphere by absorbing sunlight. BC is considered as the third most powerful climate-forcing agent in the atmosphere after CO2 and CH4 [IPCC 2013]. The uncertainties associated to BC radiative forcing are, for now, larger than 70% and are mainly related to actual measurement techniques that provide limited information to distinguish BC from other aerosols and to its optical properties [Bond 2013]. BC has been also identified as the most harmful air pollutant in terms of its adverse impacts on human health [WHO 2013]. Despite intensive efforts over the past decades, no widely accepted standard measurement method exists for the determination of BC. The most widely used methods are filter-based online aethalometry and off line thermal optical analysis. However all filter-based photometers suffer from non linearity due to the loading of the filter, which may lead to a large measurement bias [Lack 2008]. In this proposal, we propose to develop a novel Black Carbone Analyzer based on an innovative multi-channel aerosol albedometer for direct and filter-free simultaneous measurements of wavelength-dependent optical extinction and absorption of BC and other aerosols in the major spectral region of the solar radiation (300-2000 nm). This all integrated compact photonic albedometer consists of two main devices : (1) an innovative broadband optical cavity coupled to a high-sensitivity CCD spectrometer to form a BroadBand Cavity enhanced Extinctiometer (BBCE) for wavelength-resolved extinction measurements; (2) a multi-microphone enhanced Photoacoustic Absorptionmeter (PA) for wavelength-dependent integrated absorption measurements. Both devices are coupled to a single broadband high-brightness photonic light source. The implementation of the advanced photonic technologies will significantly improve the instrument performance allowing for the determination of high quality data of BC and other aerosols, such as BC and BrC fractions, their optical parameters (single scattering Albedo and complex refractive index), derived from the measured spectral data over the full spectral regions of 300-2000 nm, with a lower uncertainty of ~ 5% (compare to 20-35% of the filter based techniques [Lack 2006]). Based on the expertise acquired in our previous work, the measurement sensitivity and precision of the proposed multi-channel BBCE-PA albedometer are expected to be ~ 0.1 Mm-1 and ~ 0.5 Mm-1, respectively, with a higher temporal resolution of approximately 1 minute (compared to 1-10 minutes requested by European Environment Agency [EEA 2013]). After validation and characterization in laboratory, the BBCE-PA albedometer will be tested and calibrated in the Environnement S.A field test laboratory, and then validated via intensive field intercomparison with other field-established instruments on national and European observation network sites (like ORAURE and ACTRIS).