Discrete measurements of reactive gases and fine particle mass and composition during the 1999 Atlanta Supersite Experiment

Abstract

[1] During the Atlanta Supersite Experiment (ASSE) in August 1999, a three-channel particle composition monitor (PCM) was used to measure PM 2.5 mass and composition as well as gas-phase NH 3 , HCl, HNO 3 , HONO, SO 2 , and acetic, formic, and oxalic acids over integrating periods of 10-24 hours. The period was characterized by stagnant periods associated with high temperatures, relative humidities, and UV radiation, underlying parameters causing photochemical activity with intense ozone, and PM 2.5 formation. Analysis of diurnal measurements points to photochemical sources of HNO 3 , HONO, acetic, and formic acids. NO 2 denuder artifact reactions are assessed, and it is found that the secondary heterogeneous O 3 reaction potentially overcorrects the nitrite to nitrate oxidation step on the denuder walls, underestimating [HNO 3 ] and correspondingly overestimating [HONO]. The high ambient humidity caused gravimetric mass to be systematically high by about 20 ± 8%, which was interpreted as hydrate artifact and corrected for. Despite this correction, and inclusion of other organic elements (OOE) (OOE = 0.6 * organic carbon (OC)), an average percent fraction unidentified mass of 13 ± 10% relative to the total reported mass concentration still remained. However, if semivolatile OC collected on an XAD-coated quartz backup filter placed downstream of an XAD-denuded quartz front filter are included, an almost complete closure in the mass balance is achieved. The possible use of different OOE factors for OC and semivolatile OC (here 0.6 and 0.4, respectively) is also investigated, taking into account the different physical properties of carbon species collected from quartz front and XAD-coated quartz backup filters. It can be speculated that photochemically well-aged and well-mixed air masses contain organic compounds with more highly oxygenated and less volatile functional groups, whereas under more stagnant conditions, particle-phase organics might be less oxygenated and therefore more volatile. Sulfate and all organic compounds (including particle bound light organic acids, organic carbon, and OOE) are the main identified contributors to overall PM 2.5 mass with 32 ± 8 and 39 ± 12%, respectively. Acidity calculations based on the particle-phase SO 4 2À /NO 3 À /NH 4 + system show slightly acidic conditions.

On-Roadway In-Cabin Exposure to Particulate Matter: Measurement Results Using Both Continuous and Time-Integrated Sampling Approaches

“…This positive artifact is due to the adsorption of semi-volatile OC compounds onto the high surface area of the quartz fiber substrate of the OC filters (Mader and Pankow 2001). Previous studies have found the positive OC artifact to be 10-60% of the OC concentration (Turpin et al 2000;Subramanian et al 2004), and to be higher when sampling fresh, less photo-chemically oxidized emissions (Baumann et al 2003) or when sampling for short durations with little time for the filter to reach gas-particle phase equilibrium (Turpin et al 2000). Both of these conditions were present during the ACE-1 sampling sessions and likely contribute to the elevated OC artifacts observed.…”

Fine Particulate Matter Source Apportionment for the Chemical Speciation Trends Network Site at Birmingham, Alabama, Using Positive Matrix Factorization

“…Coincidentally, the factor 1.4 has been widely used in the past, originating from very limited theoretical and laboratory studies from more than 20 yr ago that suggested this value to be the lowest reasonable estimate for urban aerosols. 48 -50 More recent investigations, 51,52 however, suggest a factor of 1.6 Ϯ 0.2 and 2.1 Ϯ 0.2 to be more accurate in urban and nonurban environments during the summer, respectively. Our summer value is slightly lower and possibly indicative of this particular site being more heavily influenced by primary emissions from nearby industrial sources, making the influence from secondary atmospheric sources less important.…”

Investigation of molar volume and surfactant characteristics of water-soluble organic compounds in biomass burning aerosol

“…WSOC is extracted with 125 ml of pure water from the filter by sonication in a heated water bath (∼60 • C) (Baumann et al, 2003;Sullivan and Weber, 2006b) for 1.25 h. A portion of this sample (BB) was then fractionated into hydrophilic (HPHIL) and hydrophobic (HPHOB) components using a macro-porous nonionic resin (XAD-8) Solid Phase Extraction (SPE) column (Duarte and Duarte, 2005;Sullivan and Weber, 2006a). With the WSOC solution adjusted to pH=2 using HCl, the resin does not retain hydrophilic compounds.…”