Anthropogenic emissions of aerosols and trace gases from East Asia have significant impacts on air quality and climate on regional and global scales. We conducted intensive measurements of aerosols at a remote site (Cape Fuguei; 25.30°N, 121.54°E) in Taiwan in the spring of 2017, focusing on the chemical composition and mixing state of aerosols in Asian outflow. A laser‐induced incandescence–mass spectrometric analyzer (LII‐MS) was used to measure the chemical composition of aerosols internally or externally mixed with black carbon (BC). Offline analysis by transmission electron microscopy (TEM) was used to characterize the mixing state of aerosols. The observation period was classified into long‐range transport (LRT) periods and local pollution periods on the basis of cluster analysis of 3‐day backward trajectories. LII‐MS data showed that the average mass fractions of sulfate and nitrate internally mixed with BC were 7% ± 13% and 11% ± 15%, respectively, for high‐pollution episodes during LRT periods. By TEM analysis of selected samples from LRT periods, the number fraction of aerosol particles internally mixed with BC was estimated to be 5%–36% for core–shell types and 5%–23% for attached types. Factors affecting the differences between LII‐MS and TEM measurements are discussed. TEM data indicated the presence of a variety of aerosol mixing states in widespread regional pollution transported 500–1,000 km downwind of emission sources. Our results provide new constraints for three‐dimensional models that might resolve the mixing state of aerosol particles, which are critical for accurately estimating the radiative impact of BC.
Routine calibrations of online aerosol chemical composition analyzers are important for assessing data quality during field measurements. The combination of a differential mobility analyzer (DMA) and condensation particle counter (CPC) is a reliable, conventional method for calibrations. However, some logistical issues arise, including the use of radioactive material, quality control, and deployment costs. Herein, we propose a new, simple calibration method for a particle mass spectrometer using polydispersed aerosol particles combined with an optical particle sizer. We used a laser-induced incandescence-mass spectrometric analyzer (LII-MS) to test the new method. Polydispersed aerosol particles of selected chemical compounds (ammonium sulfate and potassium nitrate) were generated by an aerosol atomizer. The LII section was used as an optical particle sizer for measuring number/volume size distributions of polydispersed aerosol particles. The calibration of the MS section was performed based on the mass concentrations of polydispersed aerosol particles estimated from the integration of the volume size distributions. The accuracy of the particle sizing for each compound is a key issue and was evaluated by measuring optical pulse height distributions for monodispersed ammonium sulfate and potassium nitrate particles as well as polystyrene latex particles. A comparison of the proposed method with the conventional DMA-CPC method and its potential uncertainties are discussed.
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