Secondary aerosol formation and oxidation capacity in photooxidation in the presence of Al_2O_3 seed particles and SO_2

To investigate the sensitivity of secondary aerosol formation and oxidation capacity to NOx in homogeneous and heterogeneous reactions, a series of irradiated toluene/NOx/air and ?-pinene/NOx/air experiments were conducted in smog chambers in the absence or presence of Al2O3 seed particles. Various concentrations of NOx and volatile organic compounds(VOCs) were designed to simulate secondary aerosol formation under different scenarios for NOx. Under "VOC-limited" conditions, the increasing NOx concentration suppressed secondary aerosol formation, while the increasing toluene concentration not only contributed to the increase in secondary aerosol formation, but also led to the elevated oxidation degree for the organic aerosol. Sulfate formation was suppressed with the increasing NOx due to a decreased oxidation capacity of the photooxidation system. Secondary organic aerosol(SOA) formation also decreased with the presence of high concentration of NOx, because organo-peroxy radicals(RO2) react with NOx instead of with peroxy radicals(RO2 or HO2), resulting in the formation of volatile organic products. The increasing concentration of NOx enhanced the formation of sulfate, nitrate and SOA under "NOx-limited" conditions, in which the heterogeneous reactions played an important role. In the presence of Al2O3 seed particles, a synergetic promoting effect of mineral dust and NOx on secondary aerosol formation in heterogeneous reactions was observed in the photooxidation. This synergetic effect strengthened the positive relationship between NOx and secondary aerosol formation under "NOx-limited" conditions but weakened or even overturned the negative relationship between NOx and secondary aerosol formation under "VOC-limited" conditions. Sensitivity of secondary aerosol formation to NOx seemed different in homogeneous and heterogeneous reactions, and should be both taken into account in the sensitivity study. The sensitivity of secondary aerosol formation to NOx was further investigated under "winter-like" and NH3-rich conditions. No obvious difference for the sensitivity of secondary aerosol formation except nitrate to NOx was observed.

Effects of seed particles Al2O3, Al2（SO4）3 and H2SO4 on secondary organic aerosol

Seed particles Al2O3, Al2（SO4）3 and H2SO4 were selected to investigate their effects on secondary aerosol （SA） formation in toluene/NOx photooxidation under sulfur dioxide （SO2） and ammonia （NH3）. Effect of seed particles on SA formation was related to their acid-base properties and the presence of acid or alkaline gases. Under NH3-poor condition, SA formation increased with increasing SO2 concentration due to the acid-catalyzing effect of the oxidation products of SO2 （i.e. H2SO4）, The enhancing effect of SO2 became unobvious under NH3-rieh condition, because NH3 would eliminate the acid-catalyzing effect by neutralizing the acid products. Acidic seeds H2SO4 accelerated SA formation under either SO2 or NH3 condition. Weak acidic Al2（SO4）3 seeds didn＇t affect obviously on SA formation. The inhibiting effect of amphoteric seeds Al2O3 on SA formation was related to the presence of SO2 / NH3 due to their acid-base property. Under NH3-poor condition, the inhibiting effect of Al2O3 on SA formation decreased with increasing concentration of SO2, while under NH3-rich condition, the inhibiting effect wasn＇t remarkable.

The Criterion of Choosing the Proper Seeding Particles

This paper is focused on the problem of the ability of seeding particles to follow the flow field. One of the most important factors influencing the resultant accuracy of the measurement is using the proper seeding particles for feeding the flow when measuring by PIV （Particle Image Velocimetry） method. The aim of the paper is to provide comprehensible instruction for choosing the proper type of seeding particles with regard to the flow characteristics and required measurement accuracy. The paper presents two methods with the help of which it is possible to determine the seeding particles＇ ability to follow the flow field. The first method is based on the direct calculation of the phase lag and amplitude ratio between the particle and the fluid. The calculation is based on solution of the BBO （Basset Boussinesq Oseen） equation for spherical particle. The other method results from the calculation of the particle time response, which defines the maximum frequency of disturbances, which are to be followed by the particle. In the conclusion, the method of choosing the seeding particles is proposed, depending on the required measurement accuracy.

油茶籽粉碎程度对水酶法提油效果的影响

研究油茶籽破碎程度对水酶法提取油茶籽油的得率及提油过程形成的乳状液稳定性的影响。研究结果表明,当利用刀片式粉碎机将油茶籽平均粒径减小至37.92μm时,水酶法提取油茶籽油的总油得率、清油得率分别达到96.85%和91.83%。当对油茶籽粉继续粉碎时,茶籽粉的平均粒径基本保持不变,但水酶法提油过程中乳状液稳定性增加且乳化现象加重,导致总油得率降低,使后续破乳工艺难度加大。干法粉碎和湿法粉碎对油茶籽水酶法提取所得的毛油品质无明显区别,基本理化指标符合油茶籽油国家标准,重金属含量均在0.005mg/kg的检出限水平以下,表明刀片式粉碎方式是一种安全可行的油茶籽粉碎方式。

Second organic aerosol formation from the ozonolysis of α-pinene in the presence of dry submicron ammonium sulfate aerosol

An indoor chamber facility is described for investigation of atmospheric aerosol chemistry. Two sets of α-pinene ozonolysis experiments were conducted in the presence of dry ammonium sulfate seed particle: ozone limited experiments and α-pinene limited experiments. The concentration of gas phase and particle phase species was monitored continuously by on-line instruments and recorded automatically by data sampling system. The evolution of size distribution was measured by a scanning mobility particle sizer ...