| Atmospheric particulate matter is one of the major air pollutants in our country at present, which has serious damage to human health, visibility, climate, and air quality.The physical and chemical properties of particles play a very important role in these processes. Therefore, scholars at home and abroad are paying more attention to the particle contribution and influence to air pollution ofthe Bohai sea rim region.However, understanding chemical and physical properties of aerosol particles in aged air masses after long-range transport from urban areas are rather limitedin the background areas.In this study, one regional background site was selectedin Yellow River Delta (YRD) nature reserve and adopts the online observation and offline analysis methodto investigatethe physical and chemical properties of atmospheric aerosols.The field study was conducted from April 2011 to January 2012over a period of four months comprehensive observation. This study mainly involved the characteristics of water-soluble ions in PM2.5, particle number concentrations and size distributions, single particle mixing statein different seasons and different weather.Possible pollution sources and transports were evaluated using the backward trajectories cluster method and principal component analysis method.The results showed that the annual average total water soluble ion concentration was 49.72 ug/m3 and SO42-\NCV and NH4+ were the dominant ionic species (constituting 93.6% of the total ionic mass) with their annual average concentrations of 22.48 μg/m3,12.77 μg/m3 and 11.21 μg/m3, respectively.These three ion concentrations were generally lower than those observed in major cities in China but higher than other rural and nature reserve sites, indicating that the Yellow River delta facing serious secondary mineral aerosol pollution. Ion concentrations exhibited significantly seasonal variations, and maximum values were observed in summer. Solar radiation、O3 concentrations and temperature are the main factors influencing the daily variation of SO42- and NO3-. About 62.4% of the total particleswereacidicand 32.1% of the particles were strongly acidic. Backward air trajectory analysis found that the short distances air masses from Shandong province and Beijing-Tianjin-Hebei cities clusterhad the highest ions contribution to the Yellow River Delta. Principal component analysis results showed that combustion, secondaryaerosol and dust were the main sources of the local aerosol water-soluble ions.The annual average total particle (5-10000 nm) number concentration was 12838 #/cm3, while the concentration was highest in spring and lowest in winter.Aitken mode particles had the highest proportion (60.7%) of the total particle, followed by the accumulation mode (25.2%) and nucleation mode (14.1%). Nucleation mode particles had higher number concentrations in spring and summer, while Aitken mode particles had higher number concentrations in spring and autumn. The mean growth and formation rates were calculated as 5.3 nm/h and 6.6 #/(cm3-s), respectively. Obviously diurnal variations were observed during the new particle formation (NPF) periods, suggesting that NPF events had significant effect on the daily variation of particle number concentrations.With increasing wind speed, the Aitken and accumulation mode particle numbers decreased obviously, and the particle sizes were reduced.Higher particle number concentrations (14903 #/cm3) were associated with southern and eastern air masses, and smaller diameter peaks were associated with northern air masses.In this study, aerosol particles were classified into nine particle types using transmission electron microscopy (TEM) and energy dispersive X-Ray (EDX): mineral, K-rich, Na/Mg-rich, metal/fly ash, CaSO4/Ca(NO3)2, S-rich, soot, organic matter, and NaCl particle. Particles in HF days aged through organic and inorganic gaseous condensate (including the heterogeneous reaction on the surface of the particulate matter) and physical coagulation during transport. Particles mixed intensively in HF days with increase of number fraction of the internally mixed particles but a decrease of externally mixed primary particles. Soluble sulfates and K-rich particles tend to aggregate with refractory fine particles including soot, metal/fly ash, organic, and mineral particles. Individual particle analyses clearly showed significant difference in particle abundance and compositions before, during, and after the dust storm, indicating that mixtures of various particles and heterogeneous reactions of dust mineral particles with acidic gases depended on the meteorological conditions. S-rich particles were the most abundant particles content in this study, accounts for about 86.8% of the total particulate matter. The number concentrations of larger S-rich particles (>500 nm) increased significantly in HF days. Most of the fog particle existed in the form of dropletsanddroplets were beneficial to the growth of S-rich particles and the strong particle mixing action could enlarge the S-rich particle sizes.This paper made comprehensively study of the regional background sites of the Bohai sea rim region——the Yellow River delta nature reserve.The physical and chemical properties of atmospheric particulates were investigated to provideeffective supplement for the research on air pollution in China.The results showed that the Yellow River Deltasufferedserious air pollution, which reflected the regional and complexity of current air pollution in our country.Air mass transport has become an important influencing factor onthe regional air quality.Further study on the physical and chemical properties of particulate matter inbackground region should be enhanced in future, which could provide an important theoretical basis for control countermeasures of particulate matter pollution. |
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