The IMPROVE_A Temperature Protocol for Thermal/Optical Carbon Analysis: Maintaining Consistency with a Long-Term Database

Abstract

Thermally derived carbon fractions including organic carbon (OC) and elemental carbon (EC) have been reported for the U.S. Interagency Monitoring of PROtected Visual Environments (IMPROVE) network since 1987 and have been found useful in source apportionment studies and to evaluate quartz-fiber filter adsorption of organic vapors. The IMPROVE_A temperature protocol defines temperature plateaus for thermally derived carbon fractions of 140°C for OC1, 280°C for OC2, 480°C for OC3, and 580°C for OC4 in a helium (He) carrier gas and 580°C for EC1, 740°C for EC2, and 840°C for EC3 in a 98% He/2% oxygen (O 2 ) carrier gas. These temperatures differ from those used previously because new hardware used for the IMPROVE thermal/optical reflectance (IMPROVE_TOR) protocol better represents the sample temperature than did the old hardware. A newly developed temperature calibration method demonstrates that these temperatures better represent sample temperatures in the older units used to quantify IMPROVE carbon fractions from 1987 through 2004. Only the thermal fractions are affected by changes in temperature. The OC and EC by TOR are insensitive to the change in temperature protocol, and therefore the long-term consistency of the IMPROVE database is conserved. A method to detect small quantities of O 2 in the pure He carrier gas shows that O 2 levels above 100 ppmv also affect the comparability of thermal carbon fractions but have little effect on the IMPROVE_TOR split between OC and EC.

Long-term trends of chemical characteristics and sources of fine particle in Foshan City, Pearl River Delta: 2008–2014

“…Samples were heated stepwise to produce OC fractions (OC1, OC2, OC3 and OC4 at 140°C, 280°C, 480°C and 580°C, respectively, in a helium atmosphere); OP (a pyrolyzed carbon fraction); and EC fractions (EC1, EC2, and EC3 at 580°C, 740°C and 840°C, respectively, in a 2% O 2 /98% He atmosphere). OC is defined as OC1 + OC2 + OC3 + OC4 + OP and EC is defined as EC1 + EC2 + EC3-OP Chow et al, 2007). The analyzer was calibrated daily with CH 4 .…”

Comparison of elemental and black carbon measurements during normal and heavy haze periods: implications for research

“…EC is often determined using thermal-optical protocols, such as National Institute of Occupational Safety and Health Method 5040 with correction by thermal-optical transmission (NIOSH/TOT) (Birch 1998(Birch , 2002Birch and Cary 1996;Stone et al 2010;Kaul et al 2011) or the Interagency Monitoring of Protected Visual Environments with correction by thermal-optical reflectance (IMPROVE/TOR) (Chow et al 1993(Chow et al , 2007Pavuluri et al 2011). BC cannot be measured directly but must be inferred from the particle light absorption (b ap ) through a conversion factor that is used to translate b ap to the BC mass concentration (Chow et al 2009;Biswas et al 2003).…”

U.S. National PM2.5Chemical Speciation Monitoring Networks—CSN and IMPROVE: Description of networks

“…All channels employ mass flow control and all use 47-mm diameter filters. Sampling (Chow et al, 2007); OC and EC fractions reported in 8 temperature steps Chow et al, 2008), analysis by DRI; Details in Table 4 Sunset Thermal Optical Transmittance (TOT), modified NIOSH method 5040 (RTI 2009e); OC reported in five temperature steps; Details in (Hering and Cass, 1999;Solomon et al, 2000). Therefore, for this sampler only, nitrate is the sum of nitrate measured on the Teflon front and nylon backup filter.…”

“…a PESA discontinued November 2001. (Chow et al, 2007); OC and EC reported using TOR and TOT. OC# and EC# refers to the OC and EC peak number in the thermogram since the temperature steps are fixed in time.…”