Particle size distribution, water soluble ions, and black carbon (BC) concentration in a long-term haze-fog episode were measured using a wide-range particle spectrometer (WPS), a monitor for aerosols and gases (MARGA), and an aethalometer (AE33) in Nanjing from 16 to 27 November, 2018. The observation included five processes of clean, mist, mix, haze, and fog. Combined with meteorological elements, the HYSPLIT model, and the IMPROVE model, we analyzed the particle size distribution, chemical composition, and optical properties of aerosols in different processes. The particle number size distribution (PNSD) in five processes differed: It was bimodal in mist and fog and unimodal in clean, mix, and haze. The particle surface area size distribution (PSSD) in different processes showed a bimodal distribution, and the second peak of the mix and fog processes shifted to a larger particle size at 480 nm. The dominant air masses in five processes differed and primarily originated in the northeast direction in the clean process and the southeast direction in the haze process. In the mist, mix, and fog processes local air masses dominated. NO3- was the primary component of water soluble ions, with the lowest proportion of 45.6% in the clean process and the highest proportion of 53.0% in the mix process. The ratio of NH4+ in the different processes was stable at approximately 23%. The ratio of SO42- in the clean process was 26.2%, and the ratio of other processes was approximately 20%. The average concentration of BC in the fog processes was 10,119 ngm(-3), which was 3.55, 1.80, 1.60, and 1.46 times that in the processes of clean, mist, mix, and haze, respectively. In the different processes, BC was primarily based on liquid fuel combustion. NO3-, SO42-, and BC were the main contributors to the atmospheric extinction coefficient and contributed more than 90% in different processes. NO3- contributed 398.43 Mm(-1) in the mix process, and SO42- and BC contributed 167.90 Mm(-1) and 101.19 Mm(-1), respectively, during the fog process.
Firework/firecracker (FF) burning can significantly deteriorate air quality, whereas little is known about its influences on the elemental composition and associated health risks. Fine particles (PM2.5) and trace elements were characterized based on a multi-site campaign at Chifeng, China around 2016 Chinese Spring Festival (SF). Severe pollution levels average of 57.70 μg m−3 were observed during the SF with maximum to 471.00 μg m−3 shortly after the intensive FF activities. Largely enhanced PM2.5-bound metals were found in both urban and rural sites especially for K (8.27±5.36 μg m−3) and Al (2.36±1.41 μg m−3). Ba and Sr as the tracer of fireworks also increased more than 20-fold compared to non-SF period. Accordingly, FF burning factor identified via PMF model contributed significantly to the total elemental mass (71.34±24.94%) during the SF. Its major impacts on both crustal elements as Al, Ca, K and heavy metals as Cr, Cu and Pb were both identified. Elevated non-cancer risks (0.76 to children, 0.11 to adults) and cancer risks (3.96 × 10−6) were assessed during the SF, with As, Cd, Pb exerted the most adverse threats. The FF burning contributed the second largest share of the health threats after coal combustion, accounted for 28.35% and 12.64% of non-cancer risks for children and adults, respectively, and 10.03% of cancer risks, respectively. This study provided scientific evidences for stricter firework/firecracker regulations to protect public health.
Biomass burning is one of the major sources of carbonaceous aerosols, which affects air quality, the radiation budget and human health. Field straw residue burning is a widespread type of biomass burning in Asia, while its emissions are poorly understood compared with wood burning emissions. In this study, lab-controlled straw (wheat and corn) burning experiments were designed to investigate the emission factors and light absorption properties of different biomass burning organic aerosol (BBOA) fractions, including water-soluble organic carbon (WSOC), humic-like substances (HULIS) and water-insoluble organic carbon (WISOC). The influences of biofuel moisture content and combustion efficiency on emissions are comprehensively discussed. The emission factors of PM2.5, organic carbon (OC) and elemental carbon (EC) were 9.3±3.4, 4.6±1.9 and 0.21±0.07 g kg−1 for corn burning and 8.7±5.0, 3.9±2.8 and 0.22±0.05 g kg−1 for wheat burning, generally lower than wood or forest burning emissions. Though the mass contribution of WISOC to OC (32 %–43 %) was lower than WSOC, the light absorption contribution of WISOC (57 %–84 % at 300–400 nm) surpassed WSOC due to the higher mass absorption efficiency (MAE) of WISOC. The results suggested that BBOA light absorption would be largely underestimated if only the water-soluble fractions were considered. However, the light absorption of WSOC in the near-UV range, occupying 39 %–43 % of the total extracted OC absorption at 300 nm, cannot be negligible due to the sharper increase of absorption towards shorter wavelengths compared with WISOC. HULIS were the major light absorption contributors to WSOC, due to the higher MAE of HULIS than other high-polarity WSOC components. The emission levels and light absorption of BBOA were largely influenced by the burning conditions, indicated by modified combustion efficiency (MCE) calculated by measured CO and CO2 in this study. The emission factors of PM2.5, OC, WSOC, HULIS and organic acids were enhanced under lower MCE conditions or during higher moisture straw burning experiments. Light absorption coefficients of BBOA at 365 nm were also higher under lower MCE conditions, which was mainly due to the elevated mass emission factors. Our results suggested that the influence of varied combustion efficiency on particle emissions could surpass the differences caused by different types of biofuels. Thus, the burning efficiency or conditions should be taken into consideration when estimating the influence of biomass burning. In addition, we observed that the ratios of K+/OC">K+/OC and Cl-/OC">Cl−/OC increased under higher MCE conditions due to the enhancement of potassium and chlorine released under higher fire temperatures during flaming combustion. This indicates that the potassium ion, as a commonly used biomass burning tracer, may lead to estimation uncertainty if the burning conditions are not considered.
A new type on-chip electron source based on electroformed SiOx is recently reported to show dense and efficient electron emission under low working voltage. Here we study the effect of the Si doping type of SiOx/Si substrate on the performances of the SiOx-based electron source fabricated on it. The electron source is composed of an array of parallelly integrated micro-emitters. Each micro-emitter is composed of a square nanogap with a width about 100 nm which is spaced by two concentric graphene films on the SiOx substrate. The inner graphene film contact with bottom Si electrode through a via hole opening to the bottom Si layer and the outer graphene film contact with the common metal electrode. Effective emission current and efficiency of the electron source are found to be significantly influenced by both the polarity of the driven voltage applied between the metal electrode and bottom Si layer and the polarity of the Schottky barrier at graphene-Si contact. The performances of electron sources can be optimized by choosing n-type doping of SiOx/Si substrate to make the positive influence of the two aspects achieved at the same time. An emission current up to 100 μA and emission density of 250 mA cm−2 are achieved for an optimized device with 64 micro-emitters at bias voltage of 32.8 V.
Peracetic acid (PAA) is increasingly used as an alternative disinfectant and its advanced oxidation processes (AOPs) could be useful for pollutant degradation. Co(II) or Co(III) can activate PAA to produce acetyloxyl (CH3C(O)O•) and acetylperoxyl (CH3C(O)OO•) radicals with little •OH radical formation, and Co(II)/Co(III) is cycled. For the first time, this study determined the reaction rates of PAA with Co(II) (kPAA,Co(II) = 1.70 × 101 to 6.67 × 102 M–1·s–1) and Co(III) (kPAA,Co(III) = 3.91 × 100 to 4.57 × 102 M–1·s–1) ions over the initial pH 3.0–8.2 and evaluated 30 different aromatic organic compounds for degradation by Co/PAA. In-depth investigation confirmed that CH3C(O)OO• is the key reactive species under Co/PAA for compound degradation. Assessing the structure–activity relationship between compounds’ molecular descriptors and pseudo-first-order degradation rate constants (k′PAA• in s–1) by Co/PAA showed the number of ring atoms, EHOMO, softness, and ionization potential to be the most influential, strongly suggesting the electron transfer mechanism from aromatic compounds to the acetylperoxyl radical. The radical production and compound degradation in Co/PAA are most efficient in the intermediate pH range and can be influenced by water matrix constituents of bicarbonate, phosphate, and humic acids. These results significantly improve the knowledge regarding the acetylperoxyl radical from PAA and will be useful for further development and applications of PAA-based AOPs.
The recent discovery of comammoxNitrospiraas complete nitrifiers has fundamentally renewed perceptions of nitrogen cycling in natural and engineered systems, yet little is known about the environmental controls on these newly recognized bacteria. Based on improved phylogenetic resolution through successful assembly of ten novel genomes (71-96% completeness), we provided the first biogeographic patterns for planktonic and benthic comammoxNitrospirain the Yangtze River over a 6030 km continuum. Our study revealed the widespread distributions and relative abundance of comammoxNitrospirain this large freshwater system, constituting 30 and 46% of ammonia-oxidizing prokaryotes (AOPs) and displaying 30.4- and 17.9-fold greater abundances than canonicalNitrospirarepresentatives in water and sediments, respectively. ComammoxNitrospiracontributed more to nitrifier abundances (34-87% of AOPs) in typical oligotrophic environments with a higher pH and lower temperature, particularly in the plateau (clade B), mountain and foothill (clade A) areas of the upper reach. The dominant position of planktonic comammoxNitrospirawas replaced by canonicalNitrospirasublineages I/II and ammonia-oxidizing bacteria from the plateau to downstream plain due to environmental selection, while the dissimilarity of benthic comammoxNitrospirawas moderately associated with geographic distance. A substantial decrease (83%) in benthic comammoxNitrospiraabundance occurred immediately downstream of the Three Gorges Dam, consistent with a similarly considerable decrease in overall sediment bacterial taxa. Together, this study highlights the previously unrecognized dominance of comammoxNitrospirain major river systems and underlines the importance of revisiting the distributions of and controls on nitrification processes within global freshwater environments.
