AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Evaluation of Gas and Particle Concentrations of Water Soluble Inorganic Compounds by a Semi-continuous Monitor for Aerosols and Gases in Ambient Air (MARGA)
XI CHEN, John Walker, US Environmental Protection Agency
Abstract Number: 311 Working Group: Remote and Regional Atmospheric Aerosols
Abstract Evaluation and characterization of an Ion Chromatography technique based semi-continuous Monitor for Aerosols and Gases in Ambient Air (MARGA) was conducted to identify inherent issues with automated chromatography analysis systems. The performance and accuracy assessment revealed various errors and uncertainties resulting from mis-identification and mis-integration of chromatogram peaks by MARGA automated software. To aid data reprocessing efficiency and flexibility, an alternative chromatography data processing software was adopted to further evaluate MARGA generated data for method detection limits as well as accuracy and precision. Such reprocessing and calibration significantly improved the quality of measurement data by MARGA by lowering method detection limits (by a factor of 1.5) and variability between parallel sampler boxes. Further instrument performance evaluation, diurnal patterns of observed gaseous and particulate water soluble species (NH3, SO2, HNO3, NH4+, SO42- and NO3-) as well fine particle neutralization state were addressed during an intensive field campaign. The evaluation of MARGA tool performance revealed various potential issues encountered during monitoring especially when ambient concentrations are expected to be low. Under such circumstances a bias as high as 30% could be associated with un-examined and un-screened MARGA datasets in addition to invalid data due to peak mis-identification and mis-integration. Also calibration and verification of accuracy by external standards was deemed instrumental to data accuracy given the current reliance on an internal standard to achieve such goals. Analysis of field measurements across different synoptic meteorological patterns, including a nitrate rich arctic air mass, demonstrate that the MARGA is capable of resolving rapid composition change of PM2.5 particles.