Laterite Fe–Mn deposits are widespread in South China, with the majority of Fe–Mn ore being present in residual quaternary clay beds. However, detailed geological data on the lateritization of low-iron-content carbonate rocks are rare. In this study, we present new results on the mineralogy and geochemistry, as well as a genetic model, of the Maojun laterite Fe–Mn deposit in the Lanshan area, Hunan Province, South China. The profile sequence of laterite consists of an eroded bedrock horizon at its base, an intermediate black–brown clay layer containing earthy Fe–Mn ore, and a reddish-brown clay layer with nodular ferromanganese ore in contact with reddish-brown or yellowish-brown clay on top. Field evidence and chemical analysis indicated that during lateritization, the Mn-Fe-containing carbonate rocks of the Huanggongtang (D2h) and Shetianqiao formations (D3s) saw a more significant removal of mobile elements (Mg, Ca, and Na) whilst insoluble elements (Fe, Mn, Si, Al, Pb, and Zn) exhibited persistent enrichment in situ. Discriminative diagrams of Fe–Mn mineralization, as well as the assemblage-related enrichment of Y, U, Mo, Pb, and Zn and depletion of high-field-strength elements Zr, Nb, and Th, imply that subsequent hydrothermal circulation overprinted on the previously formed hydrogenous deposit. Mineralogical studies conducted using XRD, EPMA, HR-TEM, and TIMA indicated the predominance of iron and manganese oxides; hematite, goethite, limonite, and hollandite were identified as major oxide phases and cryptomelane, pyrolusite, and coronadite were present in minute quantities. Similar minerals constitute the upper ferromanganese nodule horizons, although they possess distinct textures and concentrations. The mineralogy, geochemical associations, and Ti mass balance show a continuous vertical evolution from top to bottom in the lateritic profile. Ferromanganese concretions from the drenching zone with poorly crystallized Al–goethite, Al–hematite, limonite, Fe–kaolinite, Fe–Mn oxides and hollandite predominate in shallow parts, and microcrystalline hematite, goethite and hollandite were found in deeper layers. Mn2+ can be rapidly oxidized and precipitated on the surface of hematite and limonite as high-valence-state (Mn4+) manganese oxides and binds strongly with mobile elements (Ba, K, Pb, Zn, Ca, and Ni). Petrographical, mineralogical, and geochemical studies show that three stages comprised the formation of the Maojun laterite Fe–Mn deposit.
Abstract. Particulate amines play an important role for the particle acidity and hygroscopicity and also contribute to secondary organic aerosol mass. We investigated the sources and mixing states of particulate amines using a single-particle aerosol mass spectrometer (SPAMS) during summer and winter 2014 at a rural site in the Pearl River Delta, China. Amine-containing particles accounted for 11.1 and 9.4 % of the total detected individual particles in summer and winter, respectively. Although the increase in amine-containing particle counts mostly occurred at night, no obvious correlations between amine-containing particles and ambient relative humidity (RH) were found during the sampling period. Among the three markers we considered, the most abundant amine marker was 74(C2H5)2NH2+, which was detected in 90 and 86 % of amine-containing particles in summer and winter, followed by amine marker ions of 59(CH3)3N+, and 86(C2H5)2NCH2+ which were detected in less than 10 % of amine-containing particles during sampling period. The amine-containing particles were characterized by high fractions of carbonaceous marker ions, carbon–nitrogen fragments, sulfate, and nitrate in both summer and winter. More than 90 % of amine-containing particles were found to be internally mixed with sulfate throughout the sampling period, while the percentage of amine particles containing nitrate increased from 43 % in summer to 69 % in winter. Robust correlations between the peak intensities of amines, sulfate, and nitrate were observed, suggesting the possible formation of aminium sulfate and nitrate salts. Interestingly, only 8 % of amine particles contained ammonium in summer, while the percentage increased dramatically to 54 % in winter, indicating a relatively ammonium-poor state in summer and an ammonium-rich state in winter. The total ammonium-containing particles were investigated and showed a much lower abundance in ambient particles in summer (3.6 %) than that in winter (32.6 %), which suggests the ammonium-poor state of amine-containing particles in summer may be related to the lower abundance of ammonia/ammonium in gas and particle phases. In addition, higher abundance of amines in ammonium-containing particles than that of ammonium in amine-containing particles suggests a possible contribution of ammonium–amine exchange reactions to the low abundance of ammonium in amine-containing particles at high ambient RH (72 ± 13 %) in summer. The particle acidity of amine-containing particles is estimated via the relative acidity ratio (Ra), which is defined as the ratio of the sum of the sulfate and nitrate peak areas divided by the ammonium peak area. The Ra was 326 ± 326 in summer and 31 ± 13 in winter, indicating that the amine-containing particles were more acidic in summer than in winter. However, after including amines along with the ammonium in the acidity calculation, the new Ra′ values showed no seasonal change in summer (11 ± 4) and winter (10 ± 2), which suggests that amines could be a buffer for the particle acidity of ammonium-poor particles.
Abstract. The radiative forcing of black carbon (BC) depends strongly on its mixing state in different chemical environments. Here, we analyzed the chemical composition and mixing state of BC-containing particles by using a single particle aerosol mass spectrometer and investigated their impacts on light absorption enhancement (Eabs) at an urban (Beijing) and a rural site (Gucheng) in North China Plain. While the BC was dominantly mixed with organic carbon (OC), nitrate and sulfate at both urban and rural sites, the rural site showed much higher fraction of BC coated with OC and nitrate (36 % vs. 15 – 20 %). Moreover, the BC mixing state evolved significantly as a function of relative humidity with largely increased coatings of OC-nitrate and nitrate at high RH levels. By linking with the bulk composition of organic aerosol (OA), we found that the OC coated on BC comprised dominantly secondary OA in Beijing, while primary and secondary OA were similarly important in Gucheng. Furthermore, Eabs was highly dependent on the secondary inorganic aerosol coated on BC at both sites, while the coated primary OC also resulted in an Eabs of ~1.2 for relatively fresh BC particles at the rural site. Positive matrix factorization analysis was performed to quantify the impact of different mixing state on Eabs. Our results showed the small Eabs (1.06 ~ 1.11) for BC particles from fresh primary emissions, while the Eabs increased significantly above 1.3 when BC was aged rapidly with increased coatings of OC-nitrate or nitrate, and it can reach above 1.4 as sulfate was involved in BC aging.
Characteristics of individual particles were analyzed by a Single Particle Aerosol Mass Spectrometry(SPAMS) at Heshan super site,from 9 to 17 June 2012.3 hazy days were captured.A total of 763350 particles in the size range of 0.2~2.0 μm were chemically analyzed with both positive and negative ion spectra.The results revealed that ambient aerosol could be classified into seven major classes,including of elemental carbon(EC),organic carbon(OC),internally mixed elemental-organic carbon(ECOC),high mass organic carbon(HMOC),sea salt(Na-K),K-rich and Pb-rich particles.During the hazy days,particles contained much more secondary components,and size distribution shifted towards larger sizes.Haze facilitated the increase of particle concentration,especially for EC,ECOC and K-rich.The results also suggested that centralized burning of rice straw and the aging of EC,ECOC and K-rich substantially contributed to the formation of haze.
Ship-exhausted air pollutants could cause negative impacts on air quality, climate change, and human health. Increasing attention has been paid to investigate the impact of ship emissions on air quality. However, the conclusions are often based on a specific year, the extent to which the inter-annual variation in meteorological conditions affects the contribution is not yet fully addressed. Therefore, in this study, the Weather Research and Forecast model and the Community Multiscale Air Quality model(WRF/CMAQ) were employed to investigate the inter-annual variations in ship-contributed PM2.5 from 2010 to 2019. The Yangtze River Delta (YRD) region in China was selected as the target study area. To highlight the impact of inter-annual meteorological variations, the emission inventory and model configurations were kept the same for the 10-year simulation. We found that: (1) inter-annual meteorological variation had an evident impact on the ship-contributed PM2.5 in most coastal cities around YRD. Taking Shanghai as an example, the contribution varied between 3.05 and 5.74 µg/m3, with the fluctuation rate of ~65%; (2) the inter-annual changes in ship’s contribution showed a trend of almost simultaneous increase and decrease for most cities, which indicates that the impact of inter-annual meteorological variation was more regional than local; (3) the inter-annual changes in the northern part of YRD were significantly higher than those in the south; (4) the most significant inter-annual changes were found in summer, followed by spring, fall and winter.
Marine aerosols were measured in real-time by an on-board signal particle aerosol mass spectrometer(SPAMS) over the Southeast China Sea. The chemical compositions and size distribution characteristics of aerosol particles were obtained, and the sources and ion spectra were analyzed. The results showed that particle number concentration decreased with the distance apart from the coastal area. In the coastal area, the aerosol compositions were mainly determined by the emissions of industry, such as vessel, traffic and coal combustion etc. When it was far from the continent, aerosols were mainly affected by the sea sources. Aerosol particles during the observation period disturbed singly with a peak diameter value of 0.5 μm. Most of the particles were in the size range of 0.2 μm to 0.8 μm. High signal intensity of EC with high K+ intensity in the positive spectrum and HSO4- intensity in negative spectrum was present in the marine aerosol over the coastal area. However, the signals of NO3- and NO2- were absent in the negative spectrum. The signal intensity of EC was weak in the marine aerosol over the sea area far from the coastal area. High signal intensity of Na+ and weak Mg+,Ca+ and NaCl+ signals were present in the positive spectrum, while high signal intensity of MSA-,CN-,O- and HSO4- were present in negative spectrum which was considered to be the special ions spectrum of marine biological sources. It indicated that ambient aerosols over the observation area were influenced not only by the anthropogenic emission sources but also affected by the marine aerosol formation.
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