Inter-comparison of elemental and organic carbon mass measurements from three North American national long-term monitoring networks at a co-located site

Abstract

Carbonaceous aerosol is a major contributor to the total aerosol load and being monitored by diverse measurement approaches. Here, 10 years (2005–2015) of continuous carbonaceous aerosol measurements collected at the Centre of Atmospheric Research Experiments (CARE) in Egbert, Ontario, Canada, on quartz-fiber filters by three independent networks (Interagency Monitoring of Protected Visual Environments, IMPROVE; Canadian Air and Precipitation Monitoring Network, CAPMoN; and Canadian Aerosol Baseline Measurement, CABM) were compared. Specifically, the study evaluated how differences in sample collection and analysis affected the concentrations of total carbon (TC), organic carbon (OC), and elemental carbon (EC). Results show that different carbonaceous fractions measured by various networks were consistent and comparable in general among the three networks over the 10-year period, even with different sampling systems/frequencies, analytical protocols, and artifact corrections. The CAPMoN TC, OC, and EC obtained from the DRI model 2001 thermal–optical carbon analyzer following the IMPROVE-TOR protocol (denoted as DRI-TOR) method were lower than those determined from the IMPROVE_A TOR method by 17 %, 14 %, and 18 %, respectively. When using transmittance for charring correction, the corresponding carbonaceous fractions obtained from the Sunset-TOT were lower by as much as 30 %, 15 %, and 75 %, respectively. In comparison, the CABM TC, OC, and EC obtained from a thermal method, EnCan-Total-900 (ECT9), were higher than the corresponding fractions from IMPROVE_A TOR by 20 %–30 %, 0 %–15 %, and 60 %–80 %, respectively. Ambient OC and EC concentrations were found to increase when ambient temperature exceeded 10 ∘C. These increased ambient concentrations of OC during summer were possibly attributed to secondary organic aerosol (SOA) formation and forest fire emissions, while elevated EC concentrations were potentially influenced by forest fire emissions and increased vehicle emissions. Results also show that the pyrolyzed organic carbon (POC) obtained from the ECT9 protocol could provide additional information on SOA although more research is still needed.