Quantification of Potentially Odorous Volatile Organic Compounds from Asphalt Binders Using Head-Space Gas Chromatography

Abstract

A gas chromatograph (GC) methodology was developed that considers film thickness, aggregate surface area, and mix temperatures, since these variables are expected to influence the production of potentially odorous volatile organic compounds (VOCs). Fifteen grams of 3 mm diameter glass beads (used to simulate a single fine size aggregate) is placed in a standard GC vial, and then coated with 0.5 g of asphalt to produce a film thickness of about 11 µm. This is representative of a typical dense graded hot mix asphalt (HMA) film thickness. The sealed vials are stored in the headspace sampler oven at the desired test temperature for 1 h. During this time, the maximum agitation option on the automated headspace sampler is used to simulate the exposure of the aggregate surface to air when the mix is either mixed in the rotary drum dryer, loaded into the haul trucks, or transferred from the trucks into the paver. This methodology was used to identify and quantify more than 80 VOC compounds found in the vial headspace at 170°C (338°F); this temperature is at the high end of typical temperatures for the majority of HMA production operations. Individual compounds were grouped based on common characteristics: alkanes, heterocyclics, phthalates, aromatics, polyaromatic hydrocarbons (PAH), sulfur-containing, chlorinated, and organic acids. Of these groups, the aromatic, sulfur-containing, heterocyclics, and organic acid compounds have the highest potential for generating odors sometimes associated with HMA production operations. Five pairs of asphalt binders (one with and one without odor complaints) were evaluated using this methodology. In all cases, the asphalt with the reported complaints had either more compounds that exceeded odor thresholds or higher concentrations, or both.

Temperature-Dependent Chemical-Specific Emission Rates of Aromatics and Polyaromatic Hydrocarbons (PAHs) in Bitumen Fume

“…This method has been peer reviewed and published for over 100 compounds (10) and verified by simultaneous laboratory and field analyses. (10) A comparison of the head-space laboratory technique with field data, conducted previously by Lange and Stroup Gardiner, (11) indicated that the laboratory technique consistently over estimated the concentration of simple aromatics and PAHs by a factor of three times. While the absolute air concentrations would be expected to be affected by this bias, the relative increases of specific PAH compounds with temperature should reflect the increases in concentration that would be observed in the field.…”

“…A total of 22 bitumen samples, which spanned the range of HMA performance grades and included a number of polymer modified binders were included in the testing program. The methodology has previously been calibrated and verified by a program of simultaneous laboratory and field tests (10,11) and is accurate in identifying field inhalation exposure potential to individual compounds in asphalt fumes.…”

“…A detailed description of the methodology, calibration, and limits of detection employed in this research can be found elsewhere. (10) Five replicates were run for each asphalt and temperature, and the individual values were averaged.…”

Considering the future of anthropogenic gas-phase organic compound emissions and the increasing influence of non-combustion sources on urban air quality

“…4.1.3). SVOC pesticides, flame retardants, and off-gassing plastics are examples studied for indoor air quality (Batterman et al, 2009;Brodzik et al, 2014;Clausen et al, 2004;Faber et al, 2013;Kemmlein et al, 2003;Lewis, 2001;Wensing et al, 2005;Weschler and Nazaroff, 2008). The third is due to the generation of degradation by-products via thermal or photochemical stress, exposure to oxidants (i.e., OH, O 3 , or NO 3 ), or other reactive chemical processes.…”

“…as commercial and industrial products, processes, and materials are important, widely distributed area sources of VOCs, IVOCs, and SVOCs with variable source profiles, making their emissions and impacts difficult to observe and constrain. Our demonstration builds on relevant indoor air quality studies observing emissions and substantial SOA formation from ozone-initiated reactions with emissions from consumer products, building materials, and cleaning products (Chang et al, 2011;Destaillats et al, 2006;Gold et al, 1978;Lewis, 2001;Mitro et al, 2016;Nazaroff and Weschler, 2004;Singer et al, 2006;Weschler, 2011;Weschler and Nazaroff, 2008;Wilke et al, 2004), as well as secondary emissions from oxidative degeneration of indoor paints, varnishes, and materials (Knudsen et al, 1999;Poppendieck et al, 2007a, b;Salthammer and Fuhrmann, 2007). We outline a holistic framework to assist future research in the field and then use a multi-dataset approach to constrain emissions, which includes the most detailed emissions inventory available, laboratory analysis of product composition, a survey of consumer product material safety datasheets (MS-DSs), and calculations of emissions timescales from theory.…”