Speciation of “brown” carbon in cloud water impacted by agricultural biomass burning in eastern China

Abstract

[1] Despite growing interest in the visible light-absorbing organic component of atmospheric aerosols, referred to as "brown" carbon, our knowledge of its chemical composition remains limited. It is well accepted that biomass burning is one important source of "brown" carbon in the atmosphere. In this study, cloud water samples heavily affected by biomass burning were collected at Mount Tai (1534 m, ASL), located in Shandong province in the North China Plain in summer 2008. The samples were analyzed with high performance liquid chromatography equipped with a UV/Vis absorbance detector immediately followed by electrospray ionization and analysis using a time-of-flight (ToF) mass spectrometer. The high mass resolution and accuracy provided by the ToF mass spectrometer allow determination of the elemental composition of detected ions. Using this approach, the elemental compositions of 16 major light-absorbing compounds, which together accounted for approximately half of measured sample absorption between 300 and 400 nm, were determined. The most important classes of light-absorbing compounds were found to be nitrophenols and aromatic carbonyls. Light absorption over this wavelength range by reduced nitrogen compounds was insignificant in these samples.

Exploring the observational constraints on the simulation of brown carbon

“…Zhang et al (2017) analyzed the inflow and outflow of OA absorption during DC3 and conclude that the high absorption aloft may relate to coarse-mode OA or OA formation during convective transport. A number of studies also suggest that aqueous-phase chemistry in cloud droplets at high altitudes can produce absorbing OA (Ervens et al, 2011;Desyaterik et al, 2013). These sources of OA are not included in our simulation, and given the limited observational constraints provided by this dataset, we do not consider these data further in our study, but we agree with Zhang et al (2017) that further investigation of high-altitude BrC is needed.…”

“…Gilardoni et al, 2016). For SOA, we assume that only aromatic SOA absorbs light since experiments show most light-absorbing SOA is related to aromatic carbonyls (Jaoui et al, 2008;Desyaterik et al, 2013) and since absorption from biogenic SOA in the field (in the same region and years studied here) has been found to be negligible compared to even mild biomass burning influence (Washenfelder et al, 2015). We specify the absorption properties of aromatic SOA based on our earlier study ; these are among the highest values from laboratory experiments (MAC = 1.46 m 2 g −1 at 365 nm; Zhang et al, 2013).…”

Exploiting simultaneous observational constraints on mass and absorption to estimate the global direct radiative forcing of black carbon and brown carbon

“…5 in light of comparison with observations. Experiments show that most of the light-absorbing SOA is associated with aromatic carbonyls (Jaoui et al, 2008;Desyaterik et al, 2013;Lambe et al, 2013). Therefore we assume that aromatic SOA is Br-SOA in our simulation.…”

Observations of fine particulate nitrated phenols in four sites in northern China: concentrations, source apportionment, and secondary formation

“…Due to their strong absorption in the near-ultraviolet and visible regions, nitrated phenols are classified as poorly characterized brown carbon (BrC) (Desyaterik et al, 2013;Teich et al, 2017). Though the absorption of BrC is weak compared to that of black carbon (BC), it can enhance the absorption of solar radiation and may have an indirect effect on regional climate (Feng et al, 2013;Mohr et al, 2013;Laskin et al, 2015;Lu et al, 2015;Zhao et al, 2015).…”