An interlaboratory comparison of aerosol inorganic ion measurements by ion chromatography: implications for aerosol pH estimate

Research output: Contribution to journalArticlepeer-review

Authors

  • Shaojie Song
  • Lianfang Wei
  • Qiang Zhang
  • Yele Sun
  • Lu Lei
  • Chao Zhang
  • Xiaohong Yao
  • Dihui Chen
  • Weijun Li
  • Miaomiao Wu
  • Hezhong Tian
  • Lining Luo
  • Shengrui Tong
  • Weiran Li
  • Junling Wang
  • Guoliang Shi
  • Yanqi Huangfu
  • Yingze Tian
  • Baozhu Ge
  • Shaoli Su
  • Chao Peng
  • Yang Chen
  • Fumo Yang
  • Aleksandra Mihajlidi-zelić
  • Dragana Đorđević
  • Stefan J. Swift
  • Imogen Andrews
  • Jacqueline F. Hamilton
  • Ye Sun
  • Agung Kramawijaya
  • Jinxiu Han
  • Supattarachai Saksakulkrai
  • Clarissa Baldo
  • Siqi Hou
  • Feixue Zheng
  • Kaspar R. Daellenbach
  • Chao Yan
  • Yongchun Liu
  • Markku Kulmala
  • Pingqing Fu

Abstract

Water-soluble inorganic ions such as ammonium, nitrate and sulfate are major components of fine aerosols in the atmosphere and are widely used in the estimation of aerosol acidity. However, different experimental practices and instrumentation may lead to uncertainties in ion concentrations. Here, an intercomparison experiment was conducted in 10 different laboratories (labs) to investigate the consistency of inorganic ion concentrations and resultant aerosol acidity estimates using the same set of aerosol filter samples. The results mostly exhibited good agreement for major ions Cl−, SO2−4, NO−3, NH+4 and K+. However, F−, Mg2+ and Ca2+ were observed with more variations across the different labs. The Aerosol Chemical Speciation Monitor (ACSM) data of nonrefractory SO2−4, NO−3 and NH+4 generally correlated very well with the filter-analysis-based data in our study, but the absolute concentrations differ by up to 42 %. Cl− from the two methods are correlated, but the concentration differ by more than a factor of 3. The analyses of certified reference materials (CRMs) generally showed a good detection accuracy (DA) of all ions in all the labs, the majority of which ranged between 90 % and 110 %. The DA was also used to correct the ion concentrations to showcase the importance of using CRMs for calibration check and quality control. Better agreements were found for Cl−, SO2−4, NO−3, NH+4 and K+ across the labs after their concentrations were corrected with DA; the coefficient of variation (CV) of Cl−, SO2−4, NO−3, NH+4 and K+ decreased by 1.7 %, 3.4 %, 3.4 %, 1.2 % and 2.6 %, respectively, after DA correction. We found that the ratio of anion to cation equivalent concentrations (AE / CE) and ion balance (anions–cations) are not good indicators for aerosol acidity estimates, as the results in different labs did not agree well with each other. In situ aerosol pH calculated from the ISORROPIA II thermodynamic equilibrium model with measured ion and ammonia concentrations showed a similar trend and good agreement across the 10 labs. Our results indicate that although there are important uncertainties in aerosol ion concentration measurements, the estimated aerosol pH from the ISORROPIA II model is more consistent.

Details

Original languageEnglish
Pages (from-to)6325-6341
JournalAtmospheric Measurement Techniques
Volume13
Issue number11
Publication statusPublished - 25 Nov 2020