Online single particle analysis of chemical composition and mixing state of crop straw burning particles： from laboratory study to field measurement

Fresh straw burning （SB） particles were generated in the laboratory by the combustion of rice straw and corn straw. The chemical composition and mixing state of the fresh SB particles were investigated by an Aerosol Time-of-Flight Mass Spectrometer （ATOFMS）. Based on the mass spectral patterns, the SB particles were clustered into four major types： Salt, Organic Carbon （OC）, Elemental Carbon （EC）, and internally mixed particles of EC and OC （EC-OC）. In addition, particles containing ash, polycyclic aromatic hydrocarbons, heavy metals or nicotine were also observed. Physical and chemical changes of the SB particles immediately after the emission were analyzed with highly time-resolved data. During the aging processes, the average particle size increased steadily. Freshly emitted organic compounds were gradu- ally oxidized to more oxygenated compounds in the OC- containing particles. Meanwhile, an important displace- ment reaction （2KCI＋ SO24- KzSO4 ＋ 2C1-） was observed. The marker ions for SB particles were optimized and applied to identify the SB particles in the ambient atmosphere. The fluctuation of the number fraction of ambient SB particles sorted by ATOFMS agrees well with that of water soluble K＋ measured by an online ion chromatography, demonstrating that the optimized marker ions could be good tracers for SB particles in field measurements.

Micro-organic dust combustion considering particles thermal resistance

Organic dust flames deal with a field of science in which many complicated phenomena like pyrolysis or devolatization of solid particles and combustion of volatile particles take place. One-dimensional flame propagation in cloud of fuel mixture is analyzed in which flame structure is divided into three zones. The first zone is preheat zone in which rate of the chemical reaction is small and transfer phenomena play significant role in temperature and mass distributions. In this model, it is assumed that particles pyrolyze first to yield a gaseous fuel mixture. The second zone is reaction zone where convection and vaporization rates of the particles are small. The third zone is convection zone where diffusive terms are negligible in comparison of other terms. Non-zero Biot number is used in order to study effect of particles thermal resistance on flame characteristics. Also, effect of particle size on combustion of micro organic dust is investigated. According to obtained results, it is understood that both flame temperature and burning velocity decrease with rise in the Biot number and particle size.

Characterization of submicron particles during autumn in Beijing,China

In this study, we performed a highly time-resolved chemical characterization of nonrefractory submicron particles（NR-PM_1） in Beijing by using an Aerodyne high-resolution time-of-flight aerosol mass spectrometer（HR-ToF-AMS）. The results showed the average NR-PM_1 mass concentration to be 56.4 ± 58.0 μg/m^3, with a peak at 307.4 μg/m^3. Due to the high frequency of biomass burning in autumn, submicron particles significantly increased in organic content, which accounted for 51% of NR-PM_1 on average. Secondary inorganic aerosols（sulfate ＋ nitrate ＋ ammonium） accounted for 46% of NR-PM_1, of which sulfate,nitrate, and ammonium contributed 15%, 20%, and 11%, respectively. To determine the intrinsic relationships between the organic and inorganic species, we used the positive matrix factorization（PMF） model to merge the high-resolution mass spectra of the organic species and NO＋and NO_2~＋ions. The PMF analysis separated the mixed organic and nitrate（NO＋and NO_2~＋） spectra into four organic factors, including hydrocarbon-like organic aerosol（HOA）, oxygenated organic aerosol（OOA）, cooking organic aerosol（COA）, and biomass burning organic aerosol（BBOA）, as well as one nitrate inorganic aerosol（NIA） factor. COA（33%） and OOA（30%） contributed the most to the total organic aerosol（OA） mass, followed by BBOA（20%） and HOA（17%）. We successfully quantified the mass concentrations of the organic and inorganic nitrates by the NO＋and NO2＋ions signal in the organic and NIA factors. The organic nitrate mass varied from 0.01-6.8 μg/m^3, with an average of 1.0 ±1.1 μg/m^3, and organic nitrate components accounted for 10% of the total nitrate mass in this observation.

Individual particle analysis of aerosols collected at Lhasa City in the Tibetan Plateau

To understand the composition and major sources of aerosol particles in Lhasa City on the Tibetan Plateau （TP）, individual particles were collected from 2 February to 8 March, 2013 in Tibet University. The mean concentrations of both PM2.5 and PM10 during the sampling were 25.7 ± 21.7 and 57.2 ± 46.7 μg/m^3, respectively, much lower than those of other cities in East and South Asia, but higher than those in the remote region in TP like Nam Co, indicating minor urban pollution. Combining the observations with the meteorological parameters and back trajectory analysis, it was concluded that local sources controlled the pollution during the sampling. Transmission electron microscopy （TEM） combined with energydispersive X-ray spectra （EDS） was used to study 408 particles sampled on four days. Based on the EDS analysis, a total of 8 different particle categories were classified for all 408 particles, including Si-rich, Ca-rich, soot, K-rich, Fe-rich, Pb-rich, Al-rich and other particles. The dominant elements were Si, A1 and Ca, which were mainly attributed to mineral dust in the earth＇s crust such as feldspar and clay. Fe-, Pb-, K-, Al-rich particles and soot mainly originated from anthropogenic sources like firework combustion and biomass burning during the sampling. During the sampling, the pollution mainly came from mineral dust, while the celebration ceremony and religious ritual produced a large quantity of anthro- pogenic metal-bearing particles on 9 and 25 February 2013. Cement particles also had a minor influence. The data obtained in this study can be useful for developing pollution control strategies.

Seasonal size-segregated PM10 and PAH concentrations in a rural area of sugarcane agriculture versus a coastal urban area in Southeastern Florida, USA

Airborne particulate matter （PM） is of health and environmental concern not only in highly urbanized areas, but also in rural areas that are used for intensive agricultural purposes, In this study, PM size- segregated samples were collected simultaneously for 12 months in a small town （Belle Glade, Florida）, which is the center of a vast sugarcane growing area and at Delray Beach, a coastal city in Palm Beach County, Florida. During the winter sampling period, when sugarcane foliage is burned just before harvest- ing to reduce the amount of plant matter to be handled, PM10 levels were 50% or higher than otherwise measured, indicating that sugarcane harvesting and processing is a major local source for PM10. For the rest of the year, PM10 levels at both sites are similar, suggesting that ambient PM levels at both sites are impacted by the major urban centers in Southern Florida. During late July and early August, the PM10 levels at both sites were substantially elevated and revealed the typical red-brownish color of Saharan dust. This has been reported to occur frequently with suitable meteorological conditions over the Atlantic Ocean coupled with a Sahara dust storm event. During the sugarcane harvesting season at Belle Glade, the concentrations of PAHs associated with PM10 were up to 15 times higher than those measured during the summer growing season, indicating a substantially higher exposure of the rural population to these often mutagenic and carcinogenic compounds.