Dicarbonyls are known to be important precursors of so-called atmospheric brown carbon, significantly affecting aerosol optical properties and radiative forcing. In this systematic study we report the formation of light-absorbing nitrogen containing compounds from simple 1,2-, 1,3-, 1,4-, and 1,5-dicarbonyl + amine reactions. A combination of spectrophotometric and mass spectrometric techniques was used to characterize reaction products in solutions mimicking atmospheric particulates. Experiments with individual dicarbonyls and dicarbonyl mixtures in ammonium sulfate and glycine solutions demonstrate that nitrogen heterocycles are common structural motifs of brown carbon chromophores formed in such reaction systems. 1,4- and 1,5-dicarbonyl reaction systems, which were used as surrogates for terpene ozonolysis products, showed rapid formation of light-absorbing material and products with absorbance maxima at ∼450 nm. Synergistic effects on absorbance properties were observed in mixed (di-)carbonyl experiments, as indicated by the formation of a strong absorber in ammonium sulfate solutions containing acetaldehyde and acetylacetone. This cross-reaction oligomer shows an absorbance maximum at 385 nm, relevant for the actinic flux region of the atmosphere. This study demonstrates the complexity of secondary brown carbon formation via the imine pathway and highlights that cross-reactions with synergistic effects have to be considered an important pathway for atmospheric BrC formation.
Highly oxygenated molecules (HOMs) play an important role in the formation and evolution of secondary organic aerosols (SOA). However, the abundance of HOMs in different environments and their relation to the oxidative potential of fine particulate matter (PM) are largely unknown. Here, we investigated the relative HOM abundance and radical yield of laboratory-generated SOA and fine PM in ambient air ranging from remote forest areas to highly polluted megacities. By electron paramagnetic resonance and mass spectrometric investigations, we found that the relative abundance of HOMs especially the dimer and low volatile types in ambient fine PM was positively correlated with the formation of radicals in aqueous PM extracts. SOA from photooxidation of isoprene, ozonolysis of α-and βpinene as well as fine PM from tropical (central Amazon) and boreal (Hyytiälä, Finland) forests exhibited a higher HOM abundance and radical yield than SOA from photooxidation of naphthalene and fine PM from urban sites (Beijing, Guangzhou, Mainz, Shanghai, and Xi'an), confirming that HOMs are important constituents of biogenic SOA to generate radicals. Our study provides new insights into the chemical relationship of HOM abundance, composition, and sources with the yield of radicals by laboratory and ambient aerosols, enabling better quantification of component-specific contribution of source-or sitespecific fine PM to its climate and health effects. ASSOCIATED CONTENT Supporting Information Supporting material consists of three tables and four figures.
Among the nitrated
and oxygenated polycyclic aromatic hydrocarbons
(NPAHs and OPAHs) are some of the most hazardous substances to public
health, mainly because of their carcinogenicity and oxidative potential.
Despite these concerns, the concentrations and fate of NPAHs and OPAHs
in the atmospheric environment are largely unknown. Ambient air concentrations
of 18 NPAHs, 5 quinones, and 5 other OPAHs were determined at two
urban and one regional background sites in central Europe. At one
of the urban sites, the total (gas and particulate) concentrations
of Σ10OPAHs were 10.0 ± 9.2 ng/m3 in winter and 3.5 ± 1.6 ng/m3 in summer. The gradient
to the regional background site exceeded 1 order of magnitude. Σ18NPAH concentrations were typically 1 order of magnitude lower
than OPAHs. Among OPAHs, 9-fluorenone and (9,10)-anthraquinone were
the most abundant species, accompanied by benzanthrone in winter.
(9,10)-Anthraquinone represented two-thirds of quinones. We found
that a large fraction of the target substance particulate mass was
carried by submicrometer particles. The derived inhalation bioaccessibility
in the PM10 size fraction is found to be ≈5% of
the total ambient concentration of OPAHs and up to ≈2% for
NPAHs. For 9-fluorenone and (9,10)-anthraquinone, up to 86 and 18%,
respectively, were found at the rural site. Our results indicate that
water solubility could function as a limiting factor for bioaccessibility
of inhaled particulate NPAHs and OPAHs, without considerable effect
of surfactant lipids and proteins in the lung lining fluid.
Cerium dioxide nanoparticles and nanorods were found to exhibit much stronger scavenging activity than ·OH generation in quasi-physiological conditions.
Environmentally persistent free radicals (EPFR) are an emerging class of constituents in particulate matter (PM). They are relatively stable with lifetimes of days to years in the condensed phase, influence...
Abstract. In the aqueous phase, fine particulate matter can form reactive species (RS)
that influence the aging, properties, and health effects of atmospheric
aerosols. In this study, we explore the RS yields of aerosol samples from
a remote forest (Hyytiälä, Finland) and polluted urban locations
(Mainz, Germany; Beijing, China), and we relate the RS yields to different
chemical constituents and reaction mechanisms. Ultra-high-resolution mass
spectrometry was used to characterize organic aerosol composition, electron
paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique was
applied to determine the concentrations of ⚫OH,
O2⚫-, and carbon- or oxygen-centered organic radicals, and
a fluorometric assay was used to quantify H2O2. The aqueous
H2O2-forming potential per mass unit of ambient PM2.5
(particle diameter < 2.5 µm) was roughly the same for all
investigated samples, whereas the mass-specific yields of radicals were
lower for sampling sites with higher concentrations of PM2.5. The
abundances of water-soluble transition metals and aromatics in ambient
PM2.5 were positively correlated with the relative fraction of
⚫OH and negatively correlated with the relative fraction of
carbon-centered radicals. In contrast, highly oxygenated organic molecules
(HOM) were positively correlated with the relative fraction of
carbon-centered radicals and negatively correlated with the relative
fraction of ⚫OH. Moreover, we found that the relative fractions
of different types of radicals formed by ambient PM2.5 were comparable
to surrogate mixtures comprising transition metal ions, organic
hydroperoxide, H2O2, and humic or fulvic acids. The interplay of
transition metal ions (e.g., iron and copper ions), highly oxidized organic
molecules (e.g., hydroperoxides), and complexing or scavenging agents (e.g.,
humic or fulvic acids) leads to nonlinear concentration dependencies in
aqueous-phase RS production. A strong dependence on chemical composition
was also observed for the aqueous-phase radical yields of
laboratory-generated secondary organic aerosols (SOA) from precursor
mixtures of naphthalene and β-pinene. Our findings show how the
composition of PM2.5 can influence the amount and nature of
aqueous-phase RS, which may explain differences in the chemical reactivity
and health effects of particulate matter in clean and polluted air.
Abstract. Interaction of water with fine particulate matter leads to the formation of reactive species (RS) that may influence the aging, properties, and health effects of atmospheric aerosols. In this study, we explore the RS yields of fine PM from remote forest (Hyytiälä, Finland) and polluted urban air (Mainz, Germany and Beijing, China) and relate these yields to different chemical constituents and reaction mechanisms. Ultrahigh-resolution mass spectrometry was used to characterize organic aerosol composition, electron paramagnetic resonance (EPR) spectroscopy with a spin-trapping technique was used to determine the concentrations •OH, O2•−, and carbon- or oxygen-centered organic radicals, and a fluorometric assay was used to quantify H2O2 concentration. The mass-specific yields of radicals were lower for sampling sites with higher concentration of ambient PM2.5 (particles with a diameter
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