Jiaoshi Zhang

Identification of long-range transport pathways and potential sources of PM 2.5 and PM 10 in Beijing from 2014 to 2015

Trajectory clustering, potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) methods were applied to investigate the transport pathways and identify potential sources of PM2.5 and PM10 in different seasons from June 2014 to May 2015 in Beijing. The cluster analyses showed that Beijing was affected by trajectories from the south and southeast in summer and autumn. In winter and spring, Beijing was not only affected by the trajectories from the south and southeast, but was also affected by trajectories from the north and northwest. In addition, the analyses of the pressure profile of backward trajectories showed that backward trajectories, which have important influence on Beijing, were mainly distributed above 970hPa in summer and autumn and below 950hPa in spring and winter. This indicates that PM2.5 and PM10 were strongly affected by the near surface air masses in summer and autumn and by high altitude air masses in winter and spring. Results of PSCF and CWT analyses showed that the largest potential source areas were identified in spring, followed by winter and autumn, then summer. In addition, potential source regions of PM10 were similar to those of PM2.5. There were a clear seasonal and spatial variation of the potential source areas of Beijing and the airflow in the horizontal and vertical directions. Therefore, more effective regional emission reduction measures in Beijings surrounding provinces should be implemented to reduce emissions of regional sources in different seasons.

Design and evaluation of a unipolar aerosol particle charger with built-in electrostatic precipitator

ABSTRACT A new unipolar charger of aerosol particle has been designed and evaluated. The free ion and particle trajectories have been simulated. Four parameters, including electrical characteristics, particle loss, charging efficiency and the average charges, were varied to evaluate the charger. The experimental results show that the average discharge current was stable at 5 µA with 2.6 kV applied on the needle. The standard deviation is 0.0016 when clean air is entered in the discharging zone, as compared to the deviation of 0.024 with unfiltered ambient air which indicates that discharge current is more stable when clean air is entered. The electrostatic loss, diffusion loss and total particle loss were below about 4, 7 and 9% for all particles (sizes of 20–1000 nm), respectively. The intrinsic and extrinsic charging efficiency increased with the particle diameter. The intrinsic efficiency is practically 100% for particle diameters above 50 nm. Compared to the intrinsic efficiency, the extrinsic charging efficiency decreased by 5% given the fact that some of particles may be deposited inside the charger. As for the average particle charge number, the maximum relative error between the results of experiment and theory was less than 15%.

Design and Evaluation of an Aerosol Electrometer with Low Noise and a Wide Dynamic Range

A low-noise aerosol electrometer with a wide dynamic range has been designed for measuring the total net charge on high concentration aerosol particles within the range of −500 pA to +500 pA. The performance of the aerosol electrometer was evaluated by a series of experiments to determine linearity, sensitivity and noise. The relative errors were controlled within 5.0%, 1.0% and 0.3% at the range of −40 pA to +40 pA, ±40 pA to ±100 pA, and ±100 pA to ±500 pA respectively. The stability of the designed aerosol electrometer was found to be highly sensitive to temperature variations, but under temperature control, the root mean square noise and the peak-to-peak noise were 1.040 fA and 5.2 fA respectively, which are very close to the calculated theoretical limit of the current noise. The excellent correlation and the advantage of a wide dynamic range have been demonstrated by comparing with the designed aerosol electrometer to a commercial aerosol electrometer. A 99.7% (R2) statistical correlation was obtained; meanwhile, the designed aerosol electrometer operated well even when an overrange phenomenon appeared in the commercial aerosol electrometer.

Development of a new Portable Ultrafine Particle Sizer for Indoor Aerosol Monitoring

A new portable Ultrafine Particle Sizer based on unipolar charger and mini-plate DMA has been developed to monitor indoor aerosol. The performance of the Ultrafine Particle Sizer is discussed in detail.