Atmospheric simulation chambers continue to be indispensable tools for research in the atmospheric sciences. Insights from chamber studies are integrated into atmospheric chemical transport models, which are used for science-informed policy decisions. However, a centralized data management and access infrastructure for their scientific products had not been available in the United States and many parts of the world. ICARUS (Integrated Chamber Atmospheric data Repository for Unified Science) is an open access, searchable, web-based infrastructure for storing, sharing, discovering, and utilizing atmospheric chamber data [https://icarus.ucdavis.edu]. ICARUS has two parts: a data intake portal and a search and discovery portal. Data in ICARUS are curated, uniform, interactive, indexed on popular search engines, mirrored by other repositories, version-tracked, vocabulary-controlled, and citable. ICARUS hosts both legacy data and new data in compliance with open access data mandates. Targeted data discovery is available based on key experimental parameters, including organic reactants and mixtures that are managed using the PubChem chemical database, oxidant information, nitrogen oxide (NOx) content, alkylperoxy radical (RO2) fate, seed particle information, environmental conditions, and reaction categories. A discipline-specific repository such as ICARUS with high amounts of metadata works to support the evaluation and revision of atmospheric model mechanisms, intercomparison of data and models, and the development of new model frameworks that can have more predictive power in the current and future atmosphere. The open accessibility and interactive nature of ICARUS data may also be useful for teaching, data mining, and training machine learning models.
Abstract. Recent inventory-based analysis suggests that emissions of volatile chemical products in urban areas are now competitive with those from the transportation sector. Understanding the potential for secondary organic aerosol formation from these volatile chemical products is, therefore, critical to predicting levels of aerosol and for formulating policy to reduce aerosol exposure. It is clear that a plethora of oxygenated compounds are either emitted directly into the atmosphere or emitted indoors and later escape into the outdoors. Experimental and computationally simulated environmental chamber data provide an understanding of aerosol yield and chemistry under relevant urban conditions (5–200 ppb NO and 291–312 K) and give insight into the effect of volatile chemical products on the production of secondary organic aerosol. Benzyl alcohol, one of these volatile chemical products, is found to have a large secondary organic aerosol formation potential. At NO concentrations of ~ 80 ppb and 291 K, secondary organic aerosol mass yields for benzyl alcohol can reach 1.
Volatile organic compounds (VOCs) were measured in the Los Angeles (LA) Basin from mid-April to mid-July 2020 during the COVID-19 pandemic, as a part of the Los Angeles Air Quality Campaign (LAAQC). VOCs were quantified in over 450 samples using one- and two-dimensional gas chromatography with different detectors; mixing ratios were determined for 150 compounds associated with on- and off-road mobile, volatile chemical product, and biogenic sources. During the sampling period, traffic counts increased from ∼55% to ∼80% of pre-COVID levels. While the average afternoon combustion-derived VOCs and carbon monoxide (CO) mixing ratios did not change significantly between April–May and June–July, there was a shift in the distribution to higher mixing ratios in June–July, particularly for VOCs associated with gasoline evaporation. Compared to observations made in the last major air quality campaign in the LA Basin (CalNex-2010), emission ratios for 40 compounds relative to acetylene (VOC/acetylene) have remained similar, while emission ratios relative to CO (VOC/CO) have dropped to ∼60% of their 2010 values. This divergence in trends suggests that whereas mobile sources are still the dominant source of the combustion-derived VOCs measured in the LA Basin, there has been a shift in the mobile source sectors, with a growing contribution from sources that have lower CO/acetylene emission ratios, including off-road equipment and vehicles. In addition to the observed shift in source sector contributions, estimated OH exposure was 70–120% higher than in 2010.
Abstract. Recent inventory-based analysis suggests that emissions of volatile chemical products in urban areas are competitive with those from the transportation sector. Understanding the potential for secondary organic aerosol formation from these volatile chemical products is therefore critical to predicting levels of aerosol and for formulating policy to reduce aerosol exposure. Experimental and computationally simulated environmental chamber data provide an understanding of aerosol yield and chemistry under relevant urban conditions (5–200 ppb NO and 291–312 K) and give insight into the effect of volatile chemical products on the production of secondary organic aerosol. Benzyl alcohol, one of these volatile chemical products, is found to have a large secondary organic aerosol formation potential. At NO concentrations of ∼ 80 ppb and 291 K, secondary organic aerosol mass yields for benzyl alcohol can reach 1.
We investigate the gas-phase photo-oxidation of 2-ethoxyethanol (2-EE) initiated by the OH radical with a focus on its autoxidation pathways. Gas-phase autoxidation─intramolecular H-shifts followed by O2 addition─has recently been recognized as a major atmospheric chemical pathway that leads to the formation of highly oxygenated organic molecules (HOMs), which are important precursors for secondary organic aerosols (SOAs). Here, we examine the gas-phase oxidation pathways of 2-EE, a model compound for glycol ethers, an important class of volatile organic compounds (VOCs) used in volatile chemical products (VCPs). Both experimental and computational techniques are applied to analyze the photochemistry of the compound. We identify oxidation products from both bimolecular and autoxidation reactions from chamber experiments at varied HO2 levels and provide estimations of rate coefficients and product branching ratios for key reaction pathways. The H-shift processes of 2-EE peroxy radicals (RO2) are found to be sufficiently fast to compete with bimolecular reactions under modest NO/HO2 conditions. More than 30% of the produced RO2 are expected to undergo at least one H-shift for conditions typical of modern summer urban atmosphere, where RO2 bimolecular lifetime is becoming >10 s, which implies the potential for glycol ether oxidation to produce considerable amounts of HOMs at reduced NOx levels and elevated temperature. Understanding the gas-phase autoxidation of glycol ethers can help fill the knowledge gap in the formation of SOA derived from oxygenated VOCs emitted from VCP sources.
Abstract. Benzyl alcohol is found in many volatile chemical products (VCPs) including a number of personal care products and industrial solvents. We report here on the products of the gas-phase oxidation of benzyl alcohol by OH and its dependence on nitric oxide (NO) levels. Using a gas chromatography in tandem with a chemical ionization mass spectrometer (CIMS) and gas chromatographer with a flame ionization detector (GC-FID), we measure the branching fractions to the major gas-phase oxidation products: hydroxybenzyl alcohol (HBA) and benzaldehyde. Later-generation oxidation products from both HBA and benzaldehyde pathways are also observed. In particular, catechol is a major gas-phase product of HBA. The fraction of H abstraction from benzyl alcohol leading to benzaldehyde formation is unaffected by [NO], with an average branching fraction of (21±10) %. The fraction of OH addition leading to HBA formation (36±18) % also does not appear to vary with [NO]. Consistent with the known high SOA yields of catechol, we find that HBA has a very high secondary organic aerosol (SOA) yield. Thus, benzyl alcohol and its oxidation products efficiently produce secondary organic aerosol – under some conditions approaching unity. Insights from the present study can help elucidate the chemistry of other atmospherically relevant aromatic compounds, especially those found in VCPs.
Abstract. Benzyl alcohol is a compound that is found in many volatile chemical products (VCPs) that are primarily used in personal care products and as industrial solvents. While past work has empirically identified oxidation products, we do not understand explicit branching ratios for first-generation benzyl alcohol oxidation products, particularly over a range of [NO] conditions. Using gas chromatography (GC) in tandem with chemical ionization mass spectrometry (CIMS), we measure the branching ratios of major oxidation products, namely hydroxybenzyl alcohol (HBA) and benzaldehyde. Later-generation oxidation products from both HBA and benzaldehyde pathways are also observed. We find the H-abstraction route leading to benzaldehyde formation unaffected by [NO], with a branching ratio of ~19 %. The OH addition route, however, which leads to HBA formation, does vary with [NO]. At higher [NO], we report a branching ratio for HBA of ~45–47 % and as high as ~69 % at low [NO]. We also find that HBA has a high secondary organic aerosol (SOA) yield, for the reaction times in this study, approaching unity. HBA, therefore, likely contributes to the high SOA yield of benzyl alcohol which under some conditions can also approach unity. Insights from the present study can help elucidate the chemistry of other atmospherically-relevant aromatic compounds, especially those found in VCPs.
Abstract. Decamethylcyclopentasiloxane (D5, C10H30O5Si5) is measured at parts per trillion (ppt) levels outdoors and parts per billion (ppb) levels indoors. Primarily used in personal care products, its outdoor concentration is correlated to population density. Since understanding the aerosol formation potential of volatile chemical products is critical to understanding particulate matter in urban areas, the secondary organic aerosol yield of D5 was studied under a wide range of OH concentrations and, correspondingly, OH exposures using both batch-mode chamber and continuously run flow tube experiments. These results were comprehensively analyzed and compared to two other secondary organic aerosol (SOA) yield datasets from literature. It was found that the SOA yield from the oxidation of D5 is extremely dependent on either the OH concentration or exposure. For OH concentrations of ≲ 107 molec.cm-3 or OH exposures of ≲ 2 × 1011 molec.scm-3, the SOA yield is largely < 5 % and usually ∼ 1 %. This is significantly lower than SOA yields previously reported. Using a two-product absorptive partitioning model for the upper bound SOA yields, the stoichiometric mass fraction and absorptive partitioning coefficients are, for the first product, α1 = 0.056 and KOM,1 = 0.022 m3 µg−1; for the second product, they are α2 = 7.7 and KOM,2 = 4.3 × 10−5 m3 µg−1. Generally, there are high SOA yields (> 90 %) at OH mixing ratios of 5 × 109 molec.cm-3 or OH exposures above 1012 molec.scm-3.
