Estimating ambient particulate organic carbon concentrations and partitioning using thermal optical measurements and the volatility basis set

Abstract

We introduce a new method to estimate the mass concentration of particulate organic carbon (POC) collected on quartz filters, demonstrating it using quartz-filter samples collected in greater Pittsburgh. This method combines thermal-optical organic carbon and elemental carbon (OC/EC) analysis and the volatility basis set (VBS) to quantify the mass concentration of semi-volatile POC on the filters. The dataset includes ambient samples collected at a number of sites in both summer and winter as well as samples from a highway tunnel. As a reference we use the two-filter bare-Quartz minus Quartz-Behind-Teflon (Q-QBT) approach to estimate the adsorbed gaseous fraction of organic carbon (OC), finding a substantial fraction in both the gas and particle phases under all conditions. In the new method we use OC fractions measured during different temperature stages of the OC/EC analysis for the single bare-quartz (BQ) filter in combination with partitioning theory to predict the volatility distributions of the measured OC, which we describe with the VBS. The effective volatility bins are consistent for data from both ambient samples and primary organic aerosol (POA)-enriched tunnel samples. Consequently, with the VBS model and total OC fractions measured over different heating stages, particulate OC can be determined by using the BQ filter alone. This method can thus be applied to all quartz filter-based OC/EC analyses to estimate the POC concentration without using backup filters.

High contributions of fossil sources to more volatile organic carbon

“…For example, if C* is equal to the concentrations of organic aerosols (COA), then 50 % of OA mass will be in the particle phase (Donahue et al, 2006). Ma et al (2016) provide an empirical C * values for each desorption temperature corresponding to the measured particulate fraction on the filter,…”

“…Earlier studies (e.g., Grieshop et al, 2009c; show similar trends qualitatively. Ma et al (2016) made first efforts to link the OC fractions desorbed at different temperatures from filter samples on a thermal-optical 15 analyzer to the volatility basis set, showing that OC fractions desorbed at lower temperatures (e.g., 140 °C, 280 °C) are semivolatile.…”

“…Our sampling duration (24 h) is much longer than that of Ma et al (2016) which is 45 min or 1 h. With longer sampling duration, the loading on the quartz filter of both particulate OC and adsorbed organic vapors increase initially, however, the latter will reach a saturation point and level out. Thus, the percent bias by the adsorbed organics is smaller for longer sampling duration (Turpin et al, 2000).…”

Atomic spectrometry update – a review of advances in environmental analysis

“…The for calculating equivalent black carbon concentrations from elemental carbon data derived from thermo-optical analysis will make it easier to compare data derived from combustionbased and optical-based measurement systems. Determination of the organic carbon content of atmospheric particles, measured using a thermal-optical approach 90 suggested that H could be used as a proxy for organic C and that the elemental C fraction could then be calculated as the difference between total C and this organic C fraction. A nondestructive, fast and inexpensive FTIR approach 94, 95 could be used to predict the levels of organic and elemental C in particulate matter collected on PTFE filters.…”

“…Tirek et al 213 There have also been improvements in sample preparation for AMS. Satou et al 235 reported an improved approach that chemically separated Sr from the sample matrix then used a mixed (1:4) SrF 2 + PbF 2 target to produce intense beam currents for the measurement of 90 Sr in soil. Liu et al 236 described a method for 129 I measurement that required minimal sample preparation and so could be very useful in emergency situations in which large numbers of samples need to be analysed rapidly for contamination assessment.…”