Optical carbon analysis on Teflon filters from the FRM network in New York

Abstract

Optical carbon analysis measurements were performed on Teflon filters from the Federal Reference Method (FRM) network in New York over the period 2015–2019. The optical measurements were performed using an inline Magee Scientific OT21 transmissometer coupled to the robotic weighing system (RWS) that measures PM2.5 mass gravimetrically. Light attenuation from the Teflon filters was compared to elemental carbon (EC) measured on quartz-fiber filters across 8 locations from the Chemical Speciation Network (CSN). The coefficients of determination (R2) were highest at urban locations (where EC concentrations were highest) and lowest at the remote rural sites. The regression slopes provided mass absorption cross-sections (MAC) from 9.12 to 11.0 m2/g at 880 nm which are in agreement with literature values. Transmissometer measurements of black carbon (BC) were also compared to Aethalometer® BC as well as EC from a semi-continuous Sunset Laboratory Inc. OCEC carbon analyzer at two locations. BC estimated from the optical measurements decreased by approximately 30 % over the 2015–2019 period consistent with the replacement of older heavy duty diesel (HDD) vehicles. BC was highest across urban locations and lowest in the rural sites. At the urban locations BC was generally highest in winter and summer, whereas at the rural sites BC was highest in summer. Both locations showed the lowest BC was in spring. Weekday vs weekend analysis revealed BC was on average lower at the weekend by approximately 20 % in NYC and 9–16 % in upstate locations.