Quantitative Characterization of the Volatility Distribution of Organic Aerosols in a Polluted Urban Area: Intercomparison Between Thermodenuder and Molecular Measurements

Abstract

To quantify the volatility of organic aerosols (OA), a comprehensive campaign was conducted in the Chinese megacity. Volatility distributions of OA and particle‐phase organic nitrate (pON) were estimated based on five methods: (a) empirical method and (b) kinetic model based on the measurement of a thermodenuder (TD) coupled with an aerosol mass spectrometer; (c) Formula‐based SIMPOL model‐driven method; (d) Element‐based estimations using molecular formula measurements of OA; and (e) gas/particle partitioning. Our results demonstrate that the ambient OA volatility distribution shows good agreement between the two heating methods and the formula‐based method when assuming ambient OA was mainly composed of organic nitrate (pON), organic sulfate and acid groups using the SIMPOL model. However, the element‐based method tends to overestimate the volatility of OA compared to the above three methods, suggesting large uncertainties in the parameterizations or in the representativeness of the molecular measurements that need further refinement. The volatility of ambient OA is generally lower than that of the laboratory‐derived secondary OA, emphasizing the impact of aging. A large fraction at the higher and lower volatility ranges (approximately log C* ≤ −9 and ≥2 μg m−3) was found for pON, implying the importance of both extremely low volatile and semi‐volatile species. Overall, this study evaluates different methods for volatility estimation and gives new insight into the volatility of OA and pON in urban areas.

Bulk Quantification and Molecular Characterization of Thermal Decomposition from the Thermal Desorption of Organic Aerosol

“…In contrast, CHO and CHON compounds are mainly IVOC and SVOC, but most of them desorb above 180 °C. The volatility of CHON is consistent with the result of Chen et al that a large fraction of organic nitrate existed either at the higher or lower volatility ranges. It has been reported that the TD-related technique rely on quantitative thermal dissociation of CHON to NO 2 in the gas phase, which occurs at about 350 °C in ∼50 ms at near-ambient pressures, and at 600 °C the dissociation rate coefficient for CHON is about 4 orders of magnitude larger .…”

“…This method can be divided into two general categories according to whether it is a bulk or speciated organic measurement. The bulk organic measurement systems include an organic carbon/elemental carbon (OC/EC) analyzer and thermodenuder aerosol mass spectrometer (TD-AMS). , The speciated organic measurement systems, mostly employing mass spectrometer, include thermal desorption chemical ionization mass spectrometer (TDCIMS), thermal desorption aerosol GC/MS-FID (TAG), micro-orifice volatilization impactor-chemical ionization mass spectrometer (MOVI-CIMS), thermal-desorption proton-transfer-reaction mass spectrometer (TD-PTR-MS), and filter inlet for gases and aerosols-chemical ionization mass spectrometer (FIGAERO-CIMS). − …”

Development, Demonstration, and Evaluation of Routine Monitoring of Aerosol Carbon, Oxygen, and Sulfur Content

“…Future work remains to evaluate the instrument performance in wider ranges of aerosol loadings and source contributions, but the measurements collected here demonstrate that even relatively simple chemical composition measurements can begin to bring insight into the properties, sources, and transformations of ambient aerosols. Validation of some of the measurement parameters, such as volatility and elemental carbon, will require continued in-depth investigation as they are complex parameters that can vary depending on the method by which they are measured. , However, overall the results of this research show great promise for the ChemSpot as a monitoring instrument for unattended measurements of particle mass and composition.…”

“…Validation of some of the measurement parameters, such as volatility and elemental carbon, will require continued in-depth investigation as they are complex parameters that can vary depending on the method by which they are measured. 39,40 However, overall the results of this research show great promise for the ChemSpot as a monitoring instrument for unattended measurements of particle mass and composition.…”