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Mass spectra of (a) the Aro-OOM factor, (b) the Temp-related factor, and (c) the Aliph-OOM factor, and the elemental formulas of major peaks are labeled above them. Peaks are color-coded by n N as indicated at the top right of the figure, and the fractions of peaks grouped by n N are reported in (d) the pie charts. The gray bars are fluorinated contaminations or non-identified compounds. The nitrated phenols are drawn separately with black peaks in (a)-(c) and were not included in (d). So n N can more reliably represent the number of nitrate groups in each molecule. Diurnal patterns (Beijing time) of these three factors are shown in (e): the bold solid lines are the median values; shaded areas represent percentiles of 75 % and 25 %; and solid circles represent mean values.
Source publication
Oxygenated organic molecules (OOMs) are the crucial intermediates linking
volatile organic compounds (VOCs) to secondary organic aerosols (SOAs) in the
atmosphere, but comprehensive understanding of the characteristics of OOMs
and their formation from VOCs is still missing. Ambient observations of
OOMs using recently developed mass spectrometry tec...
Contexts in source publication
Context 1
... averaged double bond equivalent (DBE) of this factor is the largest among all factors (Table 1), with the main signals coming from compounds with DBE > 2 (Fig. 2b) and consistent with the nature of the oxidation products of aromatics (Fig. 3a). Combined with the correlation with the production rates of OH-initiated primary RO 2 from aromatics calculated by Eq. (4) (Fig. 4), this factor is supposedly dominated by aromatic-derived OOMs (the Aro-OOM factor). This factor increases from 05:00 LT with a maximum at 10:00 LT and a sub-peak around 16:00 LT (Fig. 3e), following the ...
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... products of aromatics (Fig. 3a). Combined with the correlation with the production rates of OH-initiated primary RO 2 from aromatics calculated by Eq. (4) (Fig. 4), this factor is supposedly dominated by aromatic-derived OOMs (the Aro-OOM factor). This factor increases from 05:00 LT with a maximum at 10:00 LT and a sub-peak around 16:00 LT (Fig. 3e), following the diurnal variations in the P RO 2 of C 7 -C 10 aromatics ( Fig. 4b-d) but poorly correlated with the P RO 2 of benzene (Fig. 4a). Furthermore, OOMs with eight carbon atoms have the highest signal in this factor (Fig. 2a), derived from the most abundant C 8 aromatics + styrene RO 2 (Fig. 4f). Both of these findings can be ...
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... carbon atoms. In terms of molecular formulas, the aromatic-derived OOMs have an overlap with monoterpene-derived OOMs ( Mehra et al., 2020). Monoterpenes can contribute more C 10 OOMs than aromatics (P MT-RO 2 > P C 10 Aro-RO 2 ), but aromatics play a more important role in total in this factor since they provide more RO 2 in the urban atmosphere (Fig. ...
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... factor is named due to good correlation with temperature ( Fig. 5) and shows a maximum intensity in the afternoon at around 15:00 LT (Fig. 3e). The Temp-related factor is the only one dominated by non-nitrogenous organics ( Fig. 3b and d) and has the highest effective OSc (Table 1) [5,10]) series are possibly products from RO 2 terminated by HO 2 (Reaction R2a) or closed-shell products from RO in Reactions (R3a) or (R3b). Temperature starts to rise at 06:00 LT (Fig. 12b), but ...
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... factor is named due to good correlation with temperature ( Fig. 5) and shows a maximum intensity in the afternoon at around 15:00 LT (Fig. 3e). The Temp-related factor is the only one dominated by non-nitrogenous organics ( Fig. 3b and d) and has the highest effective OSc (Table 1) [5,10]) series are possibly products from RO 2 terminated by HO 2 (Reaction R2a) or closed-shell products from RO in Reactions (R3a) or (R3b). Temperature starts to rise at 06:00 LT (Fig. 12b), but this factor does not accumulate significantly until after about 10:00 LT (Fig. 3e), when the ...
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... organics ( Fig. 3b and d) and has the highest effective OSc (Table 1) [5,10]) series are possibly products from RO 2 terminated by HO 2 (Reaction R2a) or closed-shell products from RO in Reactions (R3a) or (R3b). Temperature starts to rise at 06:00 LT (Fig. 12b), but this factor does not accumulate significantly until after about 10:00 LT (Fig. 3e), when the mixed level of NO is reduced to 1 ppb (Fig. 4f). This phenomenon suggests a probability of HO 2 -driven chemistry of this factor under low-NO conditions since NO can consume HO 2 and compete with HO 2 for RO 2 . Such low-NO atmospheric oxidation pathways have been suggested to be non-negligible in the afternoon in central ...
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... factor is dominated by organic nitrates ( Fig. 3c and d (Fig. 3e), suggesting that Table 1. Summary of molecular characteristics of nine discussed non-nitrated-phenol factors. The calculation of the relevant parameters is given in Sect. S3 in the Supplement. Major peaks of each factor are summarized in Sect. S4 in the Supplement. Note that MW is the molecular weight, OSc is the carbon ...
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... factor is dominated by organic nitrates ( Fig. 3c and d (Fig. 3e), suggesting that Table 1. Summary of molecular characteristics of nine discussed non-nitrated-phenol factors. The calculation of the relevant parameters is given in Sect. S3 in the Supplement. Major peaks of each factor are summarized in Sect. S4 in the Supplement. Note that MW is the molecular weight, OSc is the carbon oxidation ...
Citations
... The particle number size distributions at SORPES were measured during January-December 2019 using a SMPS with a nano-differential mobility analyser and a long-differential mobility analyser, covering a size range of 4-500 nm (ref. 115). The number size distributions at Wangdu were measured using a combination of a nano condensation nucleus counter system (model A11, Airmodus), a nano-SMPS (consisting of a differential mobility analyser 3085 and a CPC3776, TSI), a long-SMPS (consisting of a differential mobility analyser 3081 and a CPC3775, TSI) and a neutral cluster and air ion spectrometer (NAIS, Airel Ltd.) for the size range 1.34-661.2 ...
A key challenge in aerosol pollution studies and climate change assessment is to understand how atmospheric aerosol particles are initially formed1,2. Although new particle formation (NPF) mechanisms have been described at specific sites3–6, in most regions, such mechanisms remain uncertain to a large extent because of the limited ability of atmospheric models to simulate critical NPF processes1,7. Here we synthesize molecular-level experiments to develop comprehensive representations of 11 NPF mechanisms and the complex chemical transformation of precursor gases in a fully coupled global climate model. Combined simulations and observations show that the dominant NPF mechanisms are distinct worldwide and vary with region and altitude. Previously neglected or underrepresented mechanisms involving organics, amines, iodine oxoacids and HNO3 probably dominate NPF in most regions with high concentrations of aerosols or large aerosol radiative forcing; such regions include oceanic and human-polluted continental boundary layers, as well as the upper troposphere over rainforests and Asian monsoon regions. These underrepresented mechanisms also play notable roles in other areas, such as the upper troposphere of the Pacific and Atlantic oceans. Accordingly, NPF accounts for different fractions (10–80%) of the nuclei on which cloud forms at 0.5% supersaturation over various regions in the lower troposphere. The comprehensive simulation of global NPF mechanisms can help improve estimation and source attribution of the climate effects of aerosols.
... 60 Field observations Ambient data of toluene and oxygenated organic molecules (OOMs) from aromatic oxidation were collected during the summer in Nanjing, a megacity in eastern China. 61 Detailed description of this data has been presented in our previous study. 61 Briey, toluene was measured using a PTR-TOF-MS (Ionicon Analytik, TOF 1000 ultra), 62 while OOMs were measured by using a nitrate-ion-based chemical ionization atmospheric pressure interface time-of-ight mass spectrometer (nitrate CI-APi-TOF), with a mass resolution of 8000-12 000 Th Th −1 (Th denotes Thomsons). ...
... 61 Detailed description of this data has been presented in our previous study. 61 Briey, toluene was measured using a PTR-TOF-MS (Ionicon Analytik, TOF 1000 ultra), 62 while OOMs were measured by using a nitrate-ion-based chemical ionization atmospheric pressure interface time-of-ight mass spectrometer (nitrate CI-APi-TOF), with a mass resolution of 8000-12 000 Th Th −1 (Th denotes Thomsons). 63,64 The concentrations of OOMs were estimated via 65,66 ...
Secondary organic aerosols (SOAs) influence the Earth's climate and threaten human health. Aromatic hydrocarbons (AHs) are major precursors for SOA formation in the urban atmosphere. However, the revealed oxidation mechanism dramatically underestimates the contribution of AHs to SOA formation, strongly suggesting the importance of seeking additional oxidation pathways for SOA formation. Using toluene, the most abundant AHs, as a model system and the combination of quantum chemical method and field observations based on advanced mass spectrometry, we herein demonstrate that the second-generation oxidation of AHs can form novel epoxides (TEPOX) with high yield. Such TEPOX can further react with H2SO4 or HNO3 in the aerosol phase to form less-volatile compounds including novel non-aromatic and ring-retaining organosulfates or organonitrates through reactive uptakes, providing new candidates of AH-derived organosulfates or organonitrates for future ambient observation. With the newly revealed mechanism, the chemistry-aerosol box modeling revealed that the SOA yield of toluene oxidation can reach up to 0.35, much higher than 0.088 based on the original mechanism under the conditions of pH = 2 and 0.1 ppbv NO. This study opens a route for the formation of reactive uptake SOA precursors from AHs and significantly fills the current knowledge gap for SOA formation in the urban atmosphere.
... This is consistent with a recent study which showed that the oxygenated organic molecules (OOMs, important intermediates which bridge the conversion of VOCs to SOA) were regulated by the NO X concentration in the atmosphere of Eastern China (Y. Liu et al., 2021). The OOMs formation was facilitated under high NO X concentrations, which then promoted SOA formation. ...
A field campaign (29 May to 14 June 2018) was conducted at a mountain site in central China. The chemical composition of non‐refractory submicron particulate matter (NR‐PM1) and the particle number size distribution (PNSD) were measured, respectively. The mean NR‐PM1 mass concentration was 20.94 ± 10.14 μg m⁻³, among which organics (47%) was the most abundant component, followed by sulfate (37%), ammonium (11%), nitrate (4%), and chloride (1%). Notably, sulfate accounted for more than 70% of the secondary inorganic aerosols. Positive matrix factorization (PMF) analysis of the composition data resulted in three organic aerosol (OA) factors: hydrocarbon‐like OA (HOA), oxygenated OA I (OOA‐I), and oxygenated OA II (OOA‐II). The secondary organic aerosol (SOA) composed of the latter two factors (SOA: OOA‐I + OOA‐II) was dominant in OA (80.7%). The PMF analysis of the PNSD data yielded three factors: new particle formation related mode, growth mode, and accumulation mode, among which the last factor dominated both number and volume ratios. The sulfate formation was characterized by the sulfur oxidation ratio (SOR), heterogeneous sulfate production rate (Phet), and gaseous sulfuric acid concentration, representing secondary sulfate transformation, heterogeneous reactions, and gas phase reactions, respectively. The results showed that Phet was well correlated with both sulfate concentrations and SOR, especially during the polluted periods. Our study demonstrates that photochemically‐driven heterogeneous reactions contribute dominantly to the sulfate formation and SOA is formed predominantly by photochemical oxidation of volatile organic compounds under high temperatures and ultraviolet (UV) intensities, and NOX concentrations on Mt. Wudang during the campaign period.
... NO x profoundly influences HOM formation. First, it can regulate the atmospheric oxidation capacity and consequently affect the oxidation of VOCs [12][13][14][15] ; Second, NO x can greatly influence the extent of RO 2 radical autoxidation 16 and thus HOM composition by directly reacting with RO 2 radicals, leading to enhanced formation of organic nitrates and suppressed formation of HOM dimers 6,[17][18][19][20][21][22][23][24][25] . Up to now, the second effect remains poorly quantified, presenting an important obstacle towards a complete understanding of HOM budget and its impacts on aerosol formation in the atmosphere. ...
... Ambient HOM measurement data from two field campaigns were used to verify the role NO x in HOM formation in the real atmosphere. One campaign was conducted at a boreal forest site (SMEAR II station) in southern Finland between 15 and 24 May 2013 to represent the low-NO x environment 11 , and the other was at an urban site in east China (SORPES station) during 2 August and 6 September 2019 to represent the high-NO x environment 22 . Detailed description of the campaigns can be found in Roldin et al., 2019 11 andLiu et al., 2021 22 . ...
The interaction between nitrogen monoxide (NO) and organic peroxy radicals (RO2) greatly impacts the formation of highly oxygenated organic molecules (HOM), the key precursors of secondary organic aerosols. It has been thought that HOM production can be significantly suppressed by NO even at low concentrations. Here, we perform dedicated experiments focusing on HOM formation from monoterpenes at low NO concentrations (0 – 82 pptv). We demonstrate that such low NO can enhance HOM production by modulating the RO2 loss and favoring the formation of alkoxy radicals that can continue to autoxidize through isomerization. These insights suggest that HOM yields from typical boreal forest emissions can vary between 2.5%-6.5%, and HOM formation will not be completely inhibited even at high NO concentrations. Our findings challenge the notion that NO monotonically reduces HOM yields by extending the knowledge of RO2-NO interactions to the low-NO regime. This represents a major advance towards an accurate assessment of HOM budgets, especially in low-NO environments, which prevails in the pre-industrial atmosphere, pristine areas, and the upper boundary layer.
... SOA evolves continuously from less oxidized (LO) to more oxidized (MO) influenced by photochemical activities in the atmosphere (Ng et al., 2010;Zhang et al., 2011). Less or highly oxygenated organic molecules (OOM or HOM) may also contribute a significant fraction to SOA production (Ehn et al., 2014;Liu et al., 2021b;Zhao et al., 2021;Nie et al., 2022). ...
Unlabelled:
Organic aerosol (OA) is a major component of atmospheric particulate matter (PM) with complex composition and formation processes influenced by various factors. Emission reduction can alter both precursors and oxidants which further affects secondary OA formation. Here we provide an observational analysis of secondary OA (SOA) variation properties in Yangtze River Delta (YRD) of eastern China in response to large scale of emission reduction during Chinese New Year (CNY) holidays from 2015 to 2020, and the COVID-19 pandemic period from January to March, 2020. We found a 17% increase of SOA proportion during the COVID lockdown. The relative enrichment of SOA is also found during multi-year CNY holidays with dramatic reduction of anthropogenic emissions. Two types of oxygenated OA (OOA) influenced by mixed emissions and SOA formation were found to be the dominant components during the lockdown in YRD region. Our results highlight that these emission-reduction-induced changes in organic aerosol need to be considered in the future to optimize air pollution control measures.
Electronic supplementary material:
Supplementary material is available in the online version of this article at 10.1007/s11783-023-1714-0 and is accessible for authorized users.
... The mass spectra obtained during these urban atmosphere observations are highly complex, implying a large diversity of precursors and formation pathways of these oxygenated organic intermediates. To extract the molecular information from these extraordinarily complicated mass spectra we used a newly developed method of mass-spectral binning combined with positive matrix factorization (binPMF) 15,16 (Methods) before peak identification. The optimal PMF solutions found eight to ten factors at different locations (Extended Data Fig. 3a), of which seven were common in at least two sites. ...
... Together with factor analysis and molecular information, eight to ten factor solutions were selected for different cities, among which seven were common factors that showed up in at least two cities (Extended Data Fig. 3a). A detailed interpretation of each binPMF factor is slightly out of the scope of this study and is carried out in one of our companion studies 16 . ...
Secondary organic aerosol contributes a significant fraction to aerosol mass and toxicity. Low-volatility organic vapours are critical intermediates connecting the oxidation of volatile organic compounds to secondary organic aerosol formation. However, the direct measurement of intermediate vapours poses a great challenge. Here we present coordinated measurements of oxygenated organic molecules in the three most urbanized regions of China and determine their likely precursors, enabling us to connect secondary organic aerosol formation to various volatile organic compounds. We show that the oxidation of anthropogenic volatile organic compounds dominates oxygenated organic molecule formation, with an approximately 40% contribution from aromatics and a 40% contribution from aliphatic hydrocarbons (predominantly alkanes), a previously under-accounted class of volatile organic compounds. The irreversible condensation of these anthropogenic oxygenated organic molecules increases significantly in highly polluted conditions, accounting for a major fraction of the production of secondary organic aerosol. We find that the distribution of oxygenated organic molecules and their formation pathways are largely the same across the urbanized regions. This suggests that uniform mitigation strategies could be effective in solving air pollution issues across these highly populated city clusters. The formation of secondary organic aerosol in Chinese megacities is dominated by the condensation of anthropogenic organic vapours, according to measurements across three urbanized regions.
Iodic acid (HIO 3) is ubiquitously present in the atmosphere and has garnered extensive attention in recent years for its contribution to particle formation and growth. The understanding of its underlying formation mechanisms, especially in inland urban areas, remains severely limited. In this study, through concurrent measurements of gas-phase iodic acid and particulate iodine in the Yangtze River Delta region, we observed continuous nighttime production of iodic acid. We found that elevated concentrations of particulate iodine and ozone (O 3) are required to effectively form the nocturnal iodic acid, with the production rate of which being proportional to the product of the concentration of aerosol iodine components and ozone concentration. Furthermore, the observed particulate iodine was significantly lower than the accumulated amount of gaseous iodic acid condensation. These findings suggest that the particulate iodine species, such as those deriving from the condensation of gaseous iodic acid, do not act as the terminal products in the atmospheric iodine cycle. Instead, they can rapidly revert to the gas phase and form iodic acid through multiphase reactions. This process may explain why, in the absence of significant iodine sources on land, iodic acid can maintain relatively high concentrations and significantly contribute to particle growth.
Oxygenated organic molecules (OOMs) play an important role in the formation of secondary organic aerosols (SOAs), but the mixing states of OOMs are still unclear. This study investigates the mixing states of OOM-containing single particles from the measurements taken using a single particle aerosol mass spectrometer in Guangzhou, China in 2022. Generally, the particle counts of OOM particles and the mass concentration of secondary organic carbon (SOC) exhibited similar temporal trends throughout the entire year. The OOM particles were consistently enriched in secondary ions, including 16O−, 26CN−, 46NO2−, 62NO3−, and 97HSO4−. In contrast, the number fractions and diurnal patterns of OOM particles among the total detected particles showed similar distributions in August and October; however, the SOC ratios in fine particulate matter were quite different, suggesting that there were different mixing states of single-particle oxygenated organics. In addition, further classification results indicated that the OOM particles were more aged in October than August, even though the SOC ratios were higher in August. Furthermore, the distribution of hydrocarbon fragments exhibited a notable decrease from January to October, emphasizing the more aged state of the organics in October. In addition, the sharp increase in elemental carbon (EC)-OOM particles in the afternoon in October suggests the potential role of EC in the aging process of organics. Overall, in contrast to the bulk analysis of SOC mass concentration, the mixing states of the OOM particles provide insights into the formation process of SOAs in field studies.
