scholarly journals Temperature and volatile organic compound concentrations as controlling factors for chemical composition of <i>α</i>-pinene-derived secondary organic aerosol

2021 ◽  
Vol 21 (15) ◽  
pp. 11545-11562
Author(s):  
Louise N. Jensen ◽  
Manjula R. Canagaratna ◽  
Kasper Kristensen ◽  
Lauriane L. J. Quéléver ◽  
Bernadette Rosati ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Organic Compound ◽  
Organic Acids ◽  
Organic Acid ◽  
Elemental Composition ◽  
Volatile Organic Compound ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Oxidation Level ◽  
Volatile Organic

Abstract. This work investigates the individual and combined effects of temperature and volatile organic compound precursor concentrations on the chemical composition of particles formed in the dark ozonolysis of α-pinene. All experiments were conducted in a 5 m3 Teflon chamber at an initial ozone concentration of 100 ppb and initial α-pinene concentrations of 10 and 50 ppb, respectively; at constant temperatures of 20, 0, or −15 ∘C; and at changing temperatures (ramps) from −15 to 20 and from 20 to −15 ∘C. The chemical composition of the particles was probed using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). A four-factor solution of a positive matrix factorization (PMF) analysis of the combined HR-ToF-AMS data is presented. The PMF analysis and the elemental composition analysis of individual experiments show that secondary organic aerosol particles with the highest oxidation level are formed from the lowest initial α-pinene concentration (10 ppb) and at the highest temperature (20 ∘C). A higher initial α-pinene concentration (50 ppb) and/or lower temperature (0 or −15 ∘C) results in a lower oxidation level of the molecules contained in the particles. With respect to the carbon oxidation state, particles formed at 0 ∘C are more comparable to particles formed at −15 ∘C than to those formed at 20 ∘C. A remarkable observation is that changes in temperature during particle formation result in only minor changes in the elemental composition of the particles. Thus, the temperature at which aerosol particle formation is induced seems to be a critical parameter for the particle elemental composition. Comparison of the HR-ToF-AMS-derived estimates of the content of organic acids in the particles based on m/z 44 in the mass spectra show good agreement with results from off-line molecular analysis of particle filter samples collected from the same experiments. Higher temperatures are associated with a decrease in the absolute mass concentrations of organic acids (R-COOH) and organic acid functionalities (-COOH), while the organic acid functionalities account for an increasing fraction of the measured particle mass.

scholarly journals Temperature and VOC concentration as controlling factors for chemical composition of alpha-pinene derived secondary organic aerosol

2020 ◽  
Author(s):  
Louise N. Jensen ◽  
Manjula R. Canagaratna ◽  
Kasper Kristensen ◽  
Lauriane L. J. Quéléver ◽  
Bernadette Rosati ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Organic Acids ◽  
Organic Acid ◽  
Elemental Composition ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Particle Formation ◽  
Composition Analysis ◽  
Oxidation Level ◽  
The Individual

Abstract. This work investigates the individual and combined effects of temperature and volatile organic compound precursor concentration on the chemical composition of particles formed in the dark ozonolysis of α-pinene. All experiments were conducted in a 5 m3 Teflon chamber at an initial ozone concentration of 100 ppb and α-pinene concentrations of 10 ppb and 50 ppb, respectively, at constant temperatures of 20 °C, 0 °C, or −15 °C, and at changing temperatures (ramps) from −15 °C to 20 °C and from 20 °C to −15 °C. The chemical composition of the particles was probed using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). A four-factor solution of a Positive Matrix Factorization (PMF) analysis of combined HR-ToF-AMS data from experiments conducted under different conditions is presented. The PMF analysis as well as elemental composition analysis of individual experiments show that secondary organic aerosol particles with the highest oxidation level are formed from the lowest initial α-pinene concentration (10 ppb) and at the highest temperature (20 °C). Higher initial α-pinene concentration (50 ppb) and/or lower temperature (0 °C or −15 °C) result in lower oxidation level of the molecules contained in the particles. With respect to carbon oxidation state, particles formed at 0 °C are more comparable to particles formed at −15 °C than to those formed at 20 °C. A remarkable observation is that changes in temperature during or after particle formation result in only minor changes in the elemental composition of the particles. The temperature at which aerosol particle formation is initiated thus seems to be a critical parameter for the particle elemental composition. Comparison of the AMS derived estimates of the content of organic acids in the particles based on m/z 44 in the spectra show good agreement with results from off-line molecular analysis of particle filter samples collected from the same experiments. While higher temperatures are associated with a decrease in the absolute mass concentrations of organic acids (R-COOH) and organic acid functionalities (-COOH), the organic acid functionalities account for an increasing fraction of the measured SOA mass at higher temperatures.

scholarly journals Air Quality Predictions using Measurement-Derived Organic Gaseous and Particle Emissions in a Petrochemical-Dominated Region

2018 ◽  
Author(s):  
Craig A. Stroud ◽  
Paul A. Makar ◽  
Junhua Zhang ◽  
Michael D. Moran ◽  
Ayodeji Akingunola ◽  
...  
Keyword(s):  
Air Quality ◽  
Organic Compound ◽  
Volatile Organic Compound ◽  
Oil Sands ◽  
Organic Aerosol ◽  
Base Case ◽  
Systematic Bias ◽  
Volatile Organic ◽  
Oil Sands Mining ◽  
The Impact

Abstract. This study assesses the impact of revised volatile organic compound (VOC) and organic aerosol (OA) emissions estimates in the GEM-MACH (Global Environmental Multiscale‒Modelling Air Quality and CHemistry) chemical transport model, driven with two different emissions input datasets, using observations from the 2013 Joint Oil Sands Monitoring (JOSM) intensive field study. The first emissions dataset (base-case run) makes use of regulatory reported VOC and particulate matter emissions data for the large oil sands mining facilities in northeastern Alberta, Canada, while the second emissions dataset (sensitivity run) uses emissions estimates based on box-flight aircraft observations around specific facilities (Li et al., 2017, Zhang et al., 2017) and a mass-balance analysis (Gordon et al., 2015) to derive total facility emission rates. The preparation of model-ready emissions files for the base-case and sensitivity run is described in an accompanying paper by Zhang et al. (2017). The large increases in VOC and OA emissions in the revised emissions data set for four large oil sands mining facilities were found to improve the modeled VOC and OA concentration maxima in plumes from these facilities, as shown with the 99th percentile statistic and illustrated by case studies. The results show that the VOC emission speciation profile from each oil sand facility is unique and different from standard petrochemical-refinery emission speciation profiles used for other regions in North America. A feedback between larger long-chain alkane emissions and higher secondary organic aerosol (SOA) concentrations was found to be significant for some facilities and improved OA predictions for those plumes. The use of the revised emissions data resulted in a large improvement of the model OA bias; however, the decrease in OA correlation coefficient suggests the need for further improvements to model organic aerosol emissions and formation processes. Including intermediate volatile organic compound (IVOC) emissions as precursors to SOA and spatially allocating more PM1 POA emissions (primary organic aerosol of 1.0 μm or less in diameter) to mine-face locations are both recommended to improve OA bias and correlation further. A systematic bias in the background OA was also predicted on most flights, likely due to under-predictions in biogenic SOA formation. Overall, the weight of evidence suggests that the new aircraft-observation-derived organic emissions help to constrain better the fugitive organic emissions, which are a challenge to estimate in the creation of bottom up emission inventories. This work shows that the use of facility-specific emissions, based on direct observations, rather than generic emission factors and speciation profiles can result in improvements to model predictions of VOCs and OA. Emissions estimation techniques, such as those used to construct the inventories in our study, may therefore have beneficial impacts when applied to other regions with large sources of VOCs and OA.

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