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Dry deposition velocities (Vd) for peroxyacetyl nitrate (PAN) calculated using two community dry deposition models with different treatments of both stomatal and nonstomatal uptakes were evaluated using measurements of PAN eddy covariance fluxes over a Loblolly pine forest in July 2003. The observed daytime maximum of Vd(PAN) was ∼1.0 cm s-1 on average, while the estimates by the WRF-Chem dry deposition module (WDDM) and the Noah land surface model coupled with a photosynthesis-based Gas Exchange Model (Noah-GEM) were only 0.2 cm s-1 and 0.6 cm s-1, respectively. The observations also showed considerable PAN deposition at night with typical Vd values of 0.2-0.6 cm s-1, while the estimated values from both models were less than 0.1 cm s-1. Noah-GEM modeled more realistic stomatal resistance (Rs) than WDDM, as compared with observations of water vapor exchange fluxes. The poor performance of WDDM for stomatal uptake is mainly due to its lack of dependence on leaf area index. Thermal decomposition was found to be relatively unimportant for measured PAN fluxes as shown by the lack of a relationship between measured total surface conductance and temperature. Thus, a large part of the underprediction in Vd from both models should be caused by the underestimation of nonstomatal uptake, in particular, the cuticle uptake. Sensitivity tests on both stomatal and nonstomatal resistances terms were conducted and some recommendations were provided. Copyright 2012 by the American Geophysical Union.

Humic-like substances (HULIS) are complex macromolecules in water-soluble organic compounds containing multiple functional groups, and transition metal ions (TMs) are ubiquitous in atmospheric particles. In this study, potential physical and chemical interactions between HULIS and four TM species including Cu2+, Mn2+, Ni2+, and Zn2+ were analyzed by optical method under acidic, weakly acidic and neutral conditions. The results showed that Cu2+, Mn2+, andZn2+ only slightly enhanced mass absorption efficiency (MAE365) of HULIS in winter, and had indiscernible effects on absorption Ångström exponent (AAE) of HULIS in both seasons under all acidity conditions. All four TMs had fluorescence quenching effects on winter HULIS, and only Cu2+ had similar effects on summer HULIS, with the highest quenching coefficients found under weakly acidic condition in both seasons. The 1H-nuclear magnetic resonance (1H-NMR) and Fourier-transform infrared (FT-IR) spectra revealed that Cu2+ mainly bound with aromatic species and tightened the molecule structures of HULIS. The parallel factor analysis (PARAFAC) results extracted four components of HULIS, including low-oxidized humic-like substances (C1), N-containing compounds (C2), highly-oxidized humic-like substances (C3), and the mixing residentials (C4), from the fluorescence spectra in both winter and summer. The divergent variations of HULIS spectral components with Cu2+ additions under three acidity conditions indicated that electron-donating groups of HULIS mainly corresponded to C1 and C3, with Cu2+ binding with HULIS by replacing proton, while electron-withdrawing groups of HULIS could correspond to C2, with its connection with Cu2+ through electrostatic adsorption or colliding induced energy transfer. [ABSTRACT FROM AUTHOR]

Chronic obstructive pulmonary disease (COPD) induces serious social and economic burdens due to its high disability and mortality, the pathogenesis of which is highly involved with inflammation, oxidative stress (OS), and mechanism of mucin 5AC (MUC5AC) secretion. Lixisenatide is a selective glucagon‐like peptide 1 receptor agonist recently reported to have anti‐inflammatory properties. Our study will focus on the potential impact of lixisenatide on lipopolysaccharide (LPS)‐induced mucin secretion and inflammation in 16 human bronchial epithelial (16HBE) cells to check its potential function in COPD. 16HBE cells were treated with LPS, with or without lixisenatide (10 and 20 nM) for 1 day. Remarkably declined cell viability, enhanced lactate dehydrogenase release, activated OS, and elevated release of inflammatory cytokines were observed in LPS‐treated 16HBE cells, accompanied by the activation of nuclear factor‐κB signaling, all of which were signally reversed by lixisenatide. Moreover, elevated expression and release of MUC5AC were observed in LPS‐treated 16HBE cells but were markedly repressed by lixisenatide. Furthermore, the repressed nuclear factor erythroid 2‐related factor 2 (Nrf2) level in LPS‐treated 16HBE cells was notably rescued by lixisenatide. Lastly, following the knockdown of Nrf2, the protective function of lixisenatide on LPS‐triggered MUC5AC release in 16HBE cells was significantly abrogated. Collectively, lixisenatide ameliorated LPS‐induced expression of mucin and inflammation in bronchial epithelial cells by regulating Nrf2. [ABSTRACT FROM AUTHOR]

Phenolic compounds and aromatic acids, as oxygenated aromatic compounds, can participate in photochemical reactions to form secondary organic aerosols (SOAs), and thus strongly impact climate and human health. In the present study, on‐site combustion experiments were conducted to determine primary emissions and secondary formation of phenolic compounds and aromatic acids released from burning of a variety of solid fuels using a potential aerosol mass‐oxidation flow reactor (PAM‐OFR). Emission factors (EFs) of phenolic compounds and aromatic acids from aged samples were 1.04 to 4.04 and 0.90 to 2.80 times those in the fresh PM2.5, respectively, implying significant amounts of these compounds produced from atmospheric aging processes. Substantially different emission profiles of phenolic compounds were observed between coal and biomass burning, with coal combustion mainly released single‐ring species (82%–86% in primary and 86%–89% in secondary emissions), while biomass burning released more two‐, three‐, and four‐ring species (59%–69% in primary and 50%–58% in secondary emissions). Aromatic acids emission profiles from coal and biomass burning also differed considerably, with biomass burning producing significantly higher (>2 times) abundance of dibasic acids than coal combustion, suggesting higher potential of producing additional ‐COOH group from biomass burning. Benzenediol, cresol, dimethylphenol, 1‐pyrenol, phenanthrenol, and hydroxylbenzonic acid were identified as SOA as they were mainly formed during simulated aging processes. Benzenediol acid/phenanthrenol was much lower from biomass (3.70 ± 1.29) than coal (62.7 ± 9.61), and these values remained stable after aging, suggesting this ratio being suitable as tracer for distinguishing different fuels combustion in source apportionment analysis. Plain Language Summary: Primary and photochemically aged phenolic compounds and aromatic acids emissions from 11 combustion scenarios covering different solid fuels and two types of stoves were investigated on‐site in rural northern China. Our results proved that aging processes could significantly increase EFs for both phenolic compounds and aromatic acids. Substantially different emission profiles of phenolic compounds and aromatic acids observed between coal and biomass combustion. During the aging processes, benzene, toluene, pyrene, phenanthrene, and benzoic acid reacted with OH to produce benzenediol, cresol, dimethylphenol, 1‐pyrenol, phenanthrenol, and hydroxylbenzonic acid, and these products could be used as SOA tracers. Our findings also indicated that several species ratios, including benzenediol acid/phenanthrenol, benzenediol acid/1,5‐dihydroxynaphthalene, benzenediol acid/1,8‐dihydroxynaphthalene, benzoic acid/2,3‐and 3,5‐dimethylbenzoic acid, and o‐, m‐, and p‐toluic acids/2,3‐and 3,5‐dimethylbenzoic acid, could be used as effective source tracers considering the stability of these ratios during aging processes and the differences in these ratios between different fuels. Key Points: Aging process for solid fuel primary emissions by reacting with OH produces significant amounts of phenolic compounds and aromatic acidsCoal combustion mainly releases single‐ring phenolic compounds, and biomass burning has a higher potential of producing additional ‐COOHMass ratio of Benzenediol acid/phenanthrenol is an ideal tracer due to its stability after aging process [ABSTRACT FROM AUTHOR]

This study investigates long-term trends of criteria air pollutants, including NO2, CO, SO2, O3 and PM2.5, and (NO2+O3) measured in ten Canadian cities during the last two to three decades and associated driving forces in terms of emission reductions, perturbations from varying weather conditions and large-scale wildfires, and changes in O3 sources and sinks. Two machine-learning methods, including random forest algorithm and boosted regression trees, were used to extract deweathered mixing ratios (or mass concentrations) of the pollutants. The Mann-Kendall analysis of the deweathered and original annual average concentrations of the pollutants showed that, on the time scale of 20 years or longer, the perturbation from varying weather conditions exerted a very minor influence on the decadal trends of original annual averages (within ±2 %) in ~70 % of the cases, and a moderate influence up to 16 % of the original trends in the other 30 % cases. NO2, CO and SO2 showed decreasing trends in the last two to three decades in all the cities except CO in Montreal. O3 showed increasing trends in all the cities, except Halifax, mainly due to weakened titration reaction between O3 and NO. (NO2+O3), however, showed decreasing trends in all the cities, except Victoria, because the increase in O3 is much less than the decrease in NO2. In three of the five eastern Canadian cities, emission reductions dominated the decreasing trends in PM2.5, but no significant trends in PM2.5 were observed in the other two cites. In five western Canadian cities, increasing or no significant trends in PM2.5 were observed, likely due to unpredictable large-scale wildfires overwhelming or balancing the impacts of emission reductions on PM2.5. In addition, despite improving air quality during the last two decades in most cities, air quality health index of above 10 (representing very high-risk condition) still occasionally occurred after 2010 in western Canadian cities because of the increased large-scale wildfires. [ABSTRACT FROM AUTHOR]