In this study, measurements of size-resolved sugar and nitrophenol concentrations and their distributions during Shanghai haze episodes were performed. The primary goal was to track their possible ...source categories and investigate the contribution of biological and biomass burning aerosols to urban haze events through regional transport. The results showed that levoglucosan had the highest concentration (40–852 ng m−3) followed by 4-nitrophenol (151–768 ng m−3), sucrose (38–380 ng m−3), 4-nitrocatechol (22–154 ng m−3), and mannitol (5–160 ng m−3). Size distributions exhibited over 90% of levoglucosan and 4-nitrocatechol to the total accumulated in the fine-particle size fraction (<2.1 μm), particularly in heavier haze periods. The back trajectories further supported the fact that levoglucosan was linked to biomass-burning particles, with higher values of associated with air masses passing from biomass burning areas (fire spots) before reaching Shanghai. Other primary saccharide and nitrophenol species showed an unusually large peak in the coarse-mode size fraction (>2.1 μm), which can be correlated with emissions from local sources (biological emission). Principal component analysis (PCA) and positive matrix factorization (PMF) revealed four probable sources (biomass burning: 28%, airborne pollen: 25%, fungal spores: 24%, and combustion emission: 23%) responsible for urban haze events. Taken together, these findings provide useful insight into size-resolved source apportionment analysis via molecular markers for urban haze pollution events in Shanghai.
•Size-resolved aerosol samples were collected in Shanghai during the haze events.•Levoglucosan, 4-nitrocatechol, OC, and EC dominated in fine particles.•Sucrose, fructose and glucose dominated in coarse particles.•Sugar alcohols and some nitrophenols presented bimodal distribution.•The major sources were biomass burning, combustion, and biological emission.
In viscous, organic-rich aerosol particles containing iron, sunlight may induce anoxic conditions that stabilize reactive oxygen species (ROS) and carbon-centered radicals (CCRs). In laboratory ...experiments, we show mass loss, iron oxidation and radical formation and release from photoactive organic particles containing iron. Our results reveal a range of temperature and relative humidity, including ambient conditions, that control ROS build up and CCR persistence in photochemically active, viscous organic particles. We find that radicals can attain high concentrations, altering aerosol chemistry and exacerbating health hazards of aerosol exposure. Our physicochemical kinetic model confirmed these results, implying that oxygen does not penetrate such particles due to the combined effects of fast reaction and slow diffusion near the particle surface, allowing photochemically-produced radicals to be effectively trapped in an anoxic organic matrix.
Organic carbon in atmospheric particles comprises a large fraction of chromatographically unresolved compounds, often referred to as humic-like substances (HULIS), which influence particle properties ...and impact climate, human health, and ecosystems. To better understand its composition, a two-dimensional (2D) offline method combining size-exclusion (SEC) and reversed-phase liquid chromatography (RP-HPLC) using a new spiked gradient profile is presented. It separates HULIS into 55 fractions of different size and polarity, with estimated ranges of molecular weight and octanol/water partitioning coefficient (log P) from 160–900 g/mol and 0.2–3.3, respectively. The distribution of HULIS within the 2D size versus polarity space is illustrated with heat maps of ultraviolet absorption at 254 nm. It is found to strongly differ in a small example set of samples from a background site near Leipzig, Germany. In winter, the most intense signals were obtained for the largest molecules (>520 g/mol) with low polarity (log P ∼ 1.9), whereas in summer, smaller (225–330 g/mol) and more polar (log P ∼ 0.55) molecules dominate. The method reveals such differences in HULIS composition in a more detailed manner than previously possible and can therefore help to better elucidate the sources of HULIS in different seasons or at different sites. Analyzing Suwannee river fulvic acid as a common HULIS surrogate shows a similar polarity range, but the sizes are clearly larger than those of atmospheric HULIS.
Atmospheric hydrogen peroxide (H2O2), as an important oxidant, plays a key role in atmospheric sulfate formation, affecting the global radiation budget and causing acid rain deposition. The ...disproportionation reactions of hydroperoxyl radicals (HO2) in both gas and aqueous phases have long been considered as dominant sources for atmospheric H2O2. However, these known sources cannot explain the significant formation of H2O2 in polluted areas under the conditions of high NO levels and low ambient relative humidity (RH). Here, we show that under relatively dry conditions during daytime, atmospheric fine particles directly produce abundant gas-phase H2O2. The formation of H2O2 is verified to be by a reaction between the particle surface −OH group and HO2 radicals formed by photooxidation of chromophoric dissolved organic matters (CDOMs), which is slightly influenced by the presence of high NO levels but remarkably accelerated by water vapor and O2. In contrast to aqueous-phase chemistry, transition metal ions (TMIs) are found to significantly suppress H2O2 formation from the atmospheric fine particles. The H2O2 formed from relatively dry particles can be directly involved in in situ SO2 oxidation, leading to sulfate formation. As CDOMs are ubiquitous in atmospheric fine particles, their daytime photochemistry is expected to play important roles in formation of H2O2 and sulfate worldwide.
During haze periods in the North China Plain, extremely high NO concentrations have been observed, commonly exceeding 1 ppbv, preventing the classical gas-phase H2O2 formation through HO2 ...recombination. Surprisingly, H2O2 mixing ratios of about 1 ppbv were observed repeatedly in winter 2017. Combined field observations and chamber experiments reveal a photochemical in-particle formation of H2O2, driven by transition metal ions (TMIs) and humic-like substances (HULIS). In chamber experiments, steady-state H2O2 mixing ratios of 116 ± 83 pptv were observed upon the irradiation of TMI- and HULIS-containing particles. Correspondingly, H2O2 formation rates of about 0.2 ppbv h–1 during the initial irradiation periods are consistent with the H2O2 rates observed in the field. A novel chemical mechanism was developed explaining the in-particle H2O2 formation through a sequence of elementary photochemical reactions involving HULIS and TMIs. Dedicated box model studies of measurement periods with relative humidity >50% and PM2.5 ≥ 75 μg m–3 agree with the observed H2O2 concentrations and time courses. The modeling results suggest about 90% of the particulate sulfate to be produced from the SO2 reaction with OH and HSO3 – oxidation by H2O2. Overall, under high pollution, the H2O2-caused sulfate formation rate is above 250 ng m–3 h–1, contributing to the sulfate formation by more than 70%.
To characterize the role of dew water for the ground surface HONO distribution, nitrous acid (HONO) measurements with a Monitor for AeRosols and Gases in ambient Air (MARGA) and a LOng Path ...Absorption Photometer (LOPAP)
instrument were performed at the Leibniz Institute
for Tropospheric Research (TROPOS) research site in Melpitz, Germany, from 19 to 29 April 2018. The dew water was also collected and analyzed
from 8 to 14 May 2019 using a glass sampler. The high time
resolution of HONO measurements showed characteristic diurnal variations
that revealed that (i) vehicle emissions are a minor source of HONO at Melpitz
station; (ii) the heterogeneous conversion of NO2 to HONO on the ground surface
dominates HONO production at night; (iii) there is significant nighttime
loss of HONO with a sink strength of 0.16±0.12 ppbv h−1; and (iv) dew water with mean NO2- of 7.91±2.14 µg m−2
could serve as a temporary HONO source in the morning when the dew droplets
evaporate. The nocturnal observations of HONO and NO2 allowed the direct
evaluation of the ground uptake coefficients for these species at night:
γNO2→HONO=2.4×10-7 to 3.5×10-6, γHONO,ground=1.7×10-5 to
2.8×10-4. A chemical model demonstrated that HONO deposition
to the ground surface at night was 90 %–100 % of the calculated unknown HONO
source in the morning. These results suggest that dew water on the ground
surface was controlling the temporal HONO distribution rather than
straightforward NO2–HONO conversion. This can strongly enhance the OH
reactivity throughout the morning time or in other planted areas that provide a large
amount of ground surface based on the OH production rate calculation.
Abstract
Chlorine atoms (Cl) are highly reactive and can strongly influence the abundances of climate and air quality-relevant trace gases. Despite extensive research on molecular chlorine (Cl
2
), a ...Cl precursor, in the polar atmosphere, its sources in other regions are still poorly understood. Here we report the daytime Cl
2
concentrations of up to 1 ppbv observed in a coastal area of Hong Kong, revealing a large daytime source of Cl
2
(2.7 pptv s
−1
at noon). Field and laboratory experiments indicate that photodissociation of particulate nitrate by sunlight under acidic conditions (pH < 3.0) can activate chloride and account for the observed daytime Cl
2
production. The high Cl
2
concentrations significantly increased atmospheric oxidation. Given the ubiquitous existence of chloride, nitrate, and acidic aerosols, we propose that nitrate photolysis is a significant daytime chlorine source globally. This so far unaccounted for source of chlorine can have substantial impacts on atmospheric chemistry.
Large quantities of mineral dust particles are frequently ejected into the atmosphere through the action of wind. The surface of dust particles acts as a sink for many gases, such as sulfur dioxide. ...It is well known that under most conditions, sulfur dioxide reacts on dust particle surfaces, leading to the production of sulfate ions. In this report, for specific atmospheric conditions, we provide evidence for an alternate pathway in which a series of reactions under solar UV light produces first gaseous sulfuric acid as an intermediate product before surface-bound sulfate. Metal oxides present in mineral dust act as atmospheric photocatalysts promoting the formation of gaseous OH radicals, which initiate the conversion of SO 2 to H 2 SO 4 in the vicinity of dust particles. Under low dust conditions, this process may lead to nucleation events in the atmosphere. The laboratory findings are supported by recent field observations near Beijing, China, and Lyon, France.
Organosulfur compounds are important components of secondary organic aerosols (SOA). While the Aerodyne high-resolution time-of-flight aerosol mass spectrometer (AMS) has been extensively used in ...aerosol studies, the response of the AMS to organosulfur compounds is not well-understood. Here, we investigated the fragmentation patterns of organosulfurs and inorganic sulfates in the AMS, developed a method to deconvolve total sulfate into components of inorganic and organic origins, and applied this method in both laboratory and field measurements. Apportionment results from laboratory isoprene photooxidation experiment showed that with inorganic sulfate seed, sulfate functionality of organic origins can contribute ∼7% of SOA mass at peak growth. Results from measurements in the Southeastern U.S. showed that 4% of measured sulfate is from organosulfur compounds. Methanesulfonic acid was estimated for measurements in the coastal and remote marine boundary layer. We explored the application of this method to unit mass-resolution data, where it performed less well due to interferences. Our apportionment results demonstrate that organosulfur compounds could be a non-negligible source of sulfate fragments in AMS laboratory and field data sets. A reevaluation of previous AMS measurements over the full range of atmospheric conditions using this method could provide a global estimate/constraint on the contribution of organosulfur compounds.
The complexation of trace metal ions (TMI) was studied in size-segregated ambient aerosol particles collected at nine sites in Germany (urban, rural and coastal). Samples were analysed in terms of ...TMI (Fe, Mn, Cu), potential inorganic and organic ligands and pH. Using a thermodynamic model (E-AIM III), the concentrations of these compounds in the particle liquid phase were estimated. The resulting liquid phase concentrations were then used as input parameters for a speciation model (Visual MINTEQ) and the equilibrium complexation was calculated under realistic conditions. The complexation was found to be controlled by the availability of strong organic ligands, especially oxalate, whose occurrence in turn was governed by the formation of insoluble Ca-oxalate. Likewise, the pH influenced oxalate availability because it alters the concentrations of the chelating mono- and dianions. As a qualitative result, Fe3+ was found to be mainly complexed by oxalate, while Fe2+ and Mn2+ were rather associated with nitrate. Cu2+ showed mixed organic and nitrate complexation. Complexation by HULIS was only significant for Fe3+ and Cu2+ and was generally less important than other ligands like oxalate and nitrate. Oxalate was found to exist mainly in the solid phase while higher dicarboxylic acids mostly did not form complexes due to protonation. Complexation was shown to be influenced by season, air mass origin, particle size and sampling site.
•TMI speciation in ambient aerosols is influenced by the availability of ligands.•The availability of organic ligands is governed by pH, c(Ca2+) and c(Mg2+).•Oxalate is mainly found in the solid phase.•Fe3+ is mainly complexed by oxalate.•Season, air mass origin, sampling site and particle size affect TMI complexation.
PDF
