Evidence of major secondary organic aerosol contribution to lensing effect black carbon absorption enhancement

Abstract

Atmospheric black carbon (BC) has a strong positive, but still controversial, effect on global warming. In particular, BC absorption enhancement (E abs ) due to internal mixing with other chemical species-so-called lensing effect-is poorly assessed. This bottleneck partly relies on the lack of long-term in situ measurements of both the optical and chemical properties of BC-containing particles. Here, we present experimental and computational results showing a significant E abs increase with the aerosol photochemical aging. This was associated with the production of highly oxidized secondary organic aerosols (SOA), especially at summertime. The 3-year-long continuous aerosol chemical and optical measurements used for the present study was obtained in the Paris region, France, which might be representative of near-future air quality within developing countries. These findings suggest that SOA could represent one of the most critical chemical species to be considered within climate models.

Six-year source apportionment of submicron organic aerosols from near-continuous highly time-resolved measurements at SIRTA (Paris area, France)

“…An excellent agreement (R = 0.94, slope = 1.006 ± 0.006) between AE31 and AE33 for measuring eBC mass concentrations has been demonstrated by Drinovec et al (2015), suggesting a negligible influence of measurement uncertainties between the two instruments on quantification of eBC concentrations. In this work, the mass concentration of eBC was estimated from an attenuation measurement performed at 880 nm as described by and Zhang et al (2018). A correction factor of 1.64 was applied to raw absorption data delivered by the instrument as recommended within the ACTRIS network (Zanatta et al, 2016).…”

“…In addition to ACSM and AE33 measurements, co-located offline analyses were performed from daily (24 h) PM 2.5 filter samples, collected and analyzed for their elemental and organic carbon contents (EC and OC, respectively) following the ACTRIS recommendations (Zanatta et al, 2017;Zhang et al, 2018). Briefly, filters were collected using a lowvolume sampler (Partisol model 2025; Thermo Scientific) equipped upstream with a VOC denuder system.…”

“…When using PMF, it may be difficult to distinguish between factors with similar spectral profiles, especially for ACSM datasets, which are associated with larger uncertainties compared to AMS (Sun et al, 2012;Zhang et al, 2015;Fröhlich et al, 2015b). The source finder (SoFi) toolkit, implemented with the ME-2 solver , has been developed by to better address this limitation.…”

“…OOA can be further separated into different fractions, being for instance classified according to its atmospheric aging described as more oxidized (MO-OOA) or less oxidized (LO-OOA) compared to each other Ng et al, 2011a;Sun et al, 2018). Different OOA factors can also be identified as relevant to various sources of SOA precursors, such as anthropogenic activities (e.g., traffic and biomass burning emissions) (Gilardoni et al, 2016;Gentner et al, 2017) and biogenic emissions (e.g., isoprene and monoterpenes) (Xu et al, 2015;Zhang et al, 2018;Freney et al, 2018) in specific regions and/or seasons. Such source apportionment has the potential to assess the efficiency of air pollution mitigation by current emission control strategies.…”

“…Based on being better suited for long-term monitoring applications due to lower cost and easier maintenance than AMS, an aerosol chemical speciation monitor (ACSM) has been designed to provide continuous measurements of the main nonrefractory chemical species within submicron aerosols (Ng et al, 2011b). As for the AMS, OA mass spectra obtained by the ACSM can be used in PMF analysis for quantification of OA sources (e.g., Sun et al, 2012;Fröhlich et al, 2015b;Zhang et al, 2015). So far, several time-extended OA source apportionment studies have been reported based on ACSM measurements at various sites (Canonaco et al, 2015;Fröhlich et al, 2015a;Schlag et al, 2016;Reyes-Villegas et al, 2016;Rattanavaraha et al, 2017;Sun et al, 2018).…”