Measurements of aerosol chemistry during new particle formation events at a remote rural mountain site

Bridged-ozonolysis of mixed aromatic hydrocarbons and organic amines: Inter-inhibited decay rate, altered product yield and synergistic-effect-enhanced secondary organic aerosol formation

Ozonolysis of aromatic hydrocarbons (AHs) or organic amines (OAs) occurs via different transformation processes, with varying rate constants and contributions to secondary organic aerosol (SOA) formation. However, to date no data is available on the ozonolysis of mixtures of AHs and OAs. This study investigated the kinetics, products and SOA yield from ozonolysis of mixture of trimethylamine with styrene, toluene or m-xylene. In the mixed system, the decay rates of styrene and trimethylamine were (1.32 ± 0.26) × 10^-4 s^-1 and (0.80 ± 0.02) × 10^-4 s^-1, decreasing up to 36.5 % and 54.4 % compared with their respective individual systems. This inter-inhibition of decay rates increased the yield of main products from styrene (i.e. benzaldehyde) by 23.5 % and trimethylamine (i.e. nitromethane) by 346.4 %. Ozonolysis of styrene or trimethylamine produced formaldehyde, which acted as a bridged product connecting the ozonolysis pathways of these two substrates, altering the yields of all products. Ozonolysis of styrene to benzaldehyde determined the increase of SOA particle number concentration (from 9.5 × 10⁵ to 1.9 × 10⁶ particles cm^-3), while trimethylamine ozonolysis to N, N-dimethylformamide contributed to synergistic-effect-enhanced SOA yield (from (64.3 ± 3.5)% to (68.1 ± 4.8)%). The findings provide a novel insight into the kinetics and mechanism of ozonolysis, as well as the resulting SOA formation from mixtures of AHs and OAs, helping to comprehensively understand the transformation and fate of organics in real atmospheric environments.

Characteristics and sources of amine-containing particles in the urban atmosphere of Liaocheng, a seriously polluted city in North China during the COVID-19 outbreak

The Chinese government issued an unprecedentedly strict lockdown policy to control the spread of the novel coronavirus disease 2019 (COVID-19), significantly mitigating air pollution because of the dramatic reduction of industrial and traffic emissions. To explore the impact of COVID-19 lockdown (LCD) on organic aerosols, the mixing states and evolution processes of amine-containing particles were studied using a single particle aerosol mass spectrometer from January to March 2020 in Liaocheng, which is a seriously polluted city in North China. The counts and percentages of amine-containing particles in total obtained particles during the pre-LCD (547832, 29.8 %) were higher than those during the LCD (283983, 20.7 %) and post-LCD (102026, 18.4 %), mainly due to the reduced emission strength of amines and suppressed gas-to-particle partitioning of amines during the LCD and post-LCD. ⁷⁴(C₂H₅)₂NH₂⁺ was the most abundant amine marker, which accounted for 98.2 %, 98.4 %, and 96.7 % of all amine-containing particles during the pre-LCD, LCD, and post-LCD, respectively. Correlation analysis and temporal variations indicated that the gas-to-particle partitioning of amines was facilitated by the stronger acidic environment and lower temperature, while the effect of RH and aerosol liquid water content was minor. The A-OC particles were the most abundant type (accounting for ~40 %) throughout the observation period. The temporal profiles and correlation analysis suggested that the impact of the increased O₃ on the amines and their oxidation products (e.g., trimethylamine oxide) was minor. The identified particle types, correlation analysis, and the potential source contribution function results implied that the amine-containing particles were mainly derived from local and surrounding sources during the LCD, while those were mainly affected by long-range transport during the pre-LCD and post-LCD. Our results could deepen the comprehension of the sources and atmospheric processing of amines in the urban area of North China during the COVID-19 outbreak.

Integrated experimental and theoretical approach to probe the synergistic effect of ammonia in methanesulfonic acid reactions with small alkylamines

While new particle formation events have been observed worldwide, our fundamental understanding of the precursors remains uncertain. It has been previously shown that small alkylamines and ammonia (NH3) are key actors in sub-3 nm particle formation through reactions with acids such as sulfuric acid (H2SO4) and methanesulfonic acid (CH3S(O)(O)OH, MSA), and that water also plays a role. Because NH3 and amines co-exist in air, we carried out combined experimental and theoretical studies examining the influence of the addition of NH3 on particle formation from the reactions of MSA with methylamine (MA) and trimethylamine (TMA). Experiments were performed in a 1 m flow reactor at 1 atm and 296 K. Measurements using an ultrafine condensation particle counter (CPC) and a scanning mobility particle sizer (SMPS) show that new particle formation was systematically enhanced upon simultaneous addition of NH3 to the MSA + amine binary system, with the magnitude depending on the amine investigated. For the MSA + TMA reaction system, the addition of NH3 at ppb concentrations produced a much greater effect (i.e. order of magnitude more particles) than the addition of ∼12 000 ppm water (corresponding to ∼45-50% relative humidity). The effect of NH3 on the MSA + MA system, which is already very efficient in forming particles on its own, was present but modest. Calculations of energies, partial charges and structures of small cluster models of the multi-component particles likewise suggest synergistic effects due to NH3 in the presence of MSA and amine. The local minimum structures and the interactions involved suggest mechanisms for this effect.

Diesel Soot and Amine-Containing Organic Sulfate Aerosols in an Arctic Oil Field

The rapid decrease in Arctic sea ice is motivating development and increasing oil and gas extraction activities. However, few observations of these local Arctic emissions exist, limiting the understanding of impacts on atmospheric composition and climate. To address this knowledge gap, the chemical composition of atmospheric aerosols was measured within the North Slope of Alaska oil fields during August and September 2016 using an aerosol time-of-flight mass spectrometer (ATOFMS) and a time-of-flight aerosol chemical speciation monitor (ToF-ACSM). Plumes from oil and gas extraction activities were characterized by soot internally mixed with sulfate (matching diesel soot) and organic carbon particles containing aminium sulfate salts. Sea spray aerosol at the coastal site was frequently internally mixed with sulfate and nitrate, from multiphase chemical processing from elevated NO_x and SO₂ within the oil field. Background (nonplume) air masses were characterized by aged combustion aerosol. No periods of "clean" (nonpolluted) Arctic air were observed. The composition of the nonrefractory aerosol measured with the ACSM was similar during plume and background periods and was consistent with the mass concentrations of nonrefractory particles measured by ATOFMS. Two ultrafine aerosol growth events were observed during oil field background periods and were correlated with fine mode amine-containing particles.

Chemistry of new particle growth during springtime in the Seoul metropolitan area, Korea

New particle formation and growth events (NPEs) were frequently observed (17 out of 60 days) during April 14 to June 15, 2016 in the Seoul metropolitan area (SMA). In this study, we investigated the chemical mechanisms of new particle growth based on measurements conducted using an aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a scanning mobility particle sizer (SMPS). Both instruments were deployed as a part of the KORUS-AQ campaign (Korea-US Air Quality study). NPEs usually started around noon time between ∼11:00 and 14:00 with the appearance of an ultrafine mode peaking between ∼20 and 30 nm (in mobility diameter, D_m, measured by the SMPS operating in the range 18-947 nm) followed by the growth of this modal diameter to 50-100 nm during the next ∼6-18 h. The growth rate of NPEs during the study was on average 4.48 ± 1.39 nm/h. Comparing to the non-NPE days in SMA, NPEs occurred under the conditions of lower concentration of preexisting particles, higher ozone (48 vs 30 ppb), stronger solar radiation (2.53 vs1.20 MJ/m²), and drier air (34 vs 65%). The HR-ToF-AMS size-resolved aerosol composition measurements show that LV-OOA (low volatility oxidized organic aerosol) and sulfate were major contributors to the growth of new particles at the initial stage of NPE which mostly occurred during daytime and that the later growth which extended into nighttime was mainly contributed by semi-volatile condensable species such as nitrate and SV-OOA (semi-volatile oxygenated organic aerosol). Generally new particles grew to a modal size of ∼80 nm (12 out of 17 NPEs) over the course of an event, however, particles could grow to larger than 100 nm when nitrate concentration was high whereas particle growth was limited to ∼ 50 nm when nitrate, SV-OOA or sulfate were low.

Single particle mass spectral signatures from vehicle exhaust particles and the source apportionment of on-line PM2.5 by single particle aerosol mass spectrometry

In order to accurately apportion the many distinct types of individual particles observed, it is necessary to characterize fingerprints of individual particles emitted directly from known sources. In this study, single particle mass spectral signatures from vehicle exhaust particles in a tunnel were performed. These data were used to evaluate particle signatures in a real-world PM_2.5 apportionment study. The dominant chemical type originating from average positive and negative mass spectra for vehicle exhaust particles are EC species. Four distinct particle types describe the majority of particles emitted by vehicle exhaust particles in this tunnel. Each particle class is labeled according to the most significant chemical features in both average positive and negative mass spectral signatures, including ECOC, NaK, Metal and PAHs species. A single particle aerosol mass spectrometry (SPAMS) was also employed during the winter of 2013 in Guangzhou to determine both the size and chemical composition of individual atmospheric particles, with vacuum aerodynamic diameter (d_va) in the size range of 0.2-2μm. A total of 487,570 particles were chemically analyzed with positive and negative ion mass spectra and a large set of single particle mass spectra was collected and analyzed in order to identify the speciation. According to the typical tracer ions from different source types and classification by the ART-2a algorithm which uses source fingerprints for apportioning ambient particles, the major sources of single particles were simulated. Coal combustion, vehicle exhaust, and secondary ion were the most abundant particle sources, contributing 28.5%, 17.8%, and 18.2%, respectively. The fraction with vehicle exhaust species particles decreased slightly with particle size in the condensation mode particles.

Sources and characteristics of fine particles over the Yellow Sea and Bohai Sea using online single particle aerosol mass spectrometer

Marine aerosols over the East China Seas are heavily polluted by continental sources. During the Chinese Comprehensive Ocean Experiment in November 2012, size and mass spectra of individual atmospheric particles in the size range from 0.2 to 2.0 μm were measured on board by a single particle aerosol mass spectrometer (SPAMS). The average hourly particle number (PN) was around 4560±3240 in the South Yellow Sea (SYS), 2900±3970 in the North Yellow Sea (NYS), and 1700±2220 in the Bohai Sea (BS). PN in NYS and BS varied greatly over 3 orders of magnitude, while that in SYS varied slightly. The size distributions were fitted with two log-normal modes. Accumulation mode dominated in NYS and BS, especially during episodic periods. Coarse mode particles played an important role in SYS. Particles were classified using an adaptive resonance theory based neural network algorithm (ART-2a). Six particle types were identified with secondary-containing, aged sea-salt, soot-like, biomass burning, fresh sea-salt, and lead-containing particles accounting for 32%, 21%, 18%, 16%, 4%, and 3% of total PN, respectively. Aerosols in BS were relatively enriched in particles from anthropogenic sources compared to SYS, probably due to emissions from more developed upwind regions and indicating stronger influence of continental outflow on marine environment. Variation of source types depended mainly on origins of transported air masses. This study examined rapid changes in PN, size distribution and source types of fine particles in marine atmospheres. It also demonstrated the effectiveness of high-time-resolution source apportionment by ART-2a.

An In Situ Method for Sizing Insoluble Residues in Precipitation and Other Aqueous Samples

Particles are frequently incorporated into clouds or precipitation, influencing climate by acting as cloud condensation or ice nuclei, taking up coatings during cloud processing, and removing species through wet deposition. Many of these particles, particularly ice nuclei, can remain suspended within cloud droplets/crystals as insoluble residues. While previous studies have measured the soluble or bulk mass of species within clouds and precipitation, no studies to date have determined the number concentration and size distribution of insoluble residues in precipitation or cloud water using in situ methods. Herein, for the first time we demonstrate that Nanoparticle Tracking Analysis (NTA) is a powerful in situ method for determining the total number concentration, number size distribution, and surface area distribution of insoluble residues in precipitation, both of rain and melted snow. The method uses 500 μL or less of liquid sample and does not require sample modification. Number concentrations for the insoluble residues in aqueous precipitation samples ranged from 2.0-3.0(±0.3)×10⁸ particles cm^-3, while surface area ranged from 1.8(±0.7)-3.2(±1.0)×10⁷ μm² cm^-3. Number size distributions peaked between 133-150 nm, with both single and multi-modal character, while surface area distributions peaked between 173-270 nm. Comparison with electron microscopy of particles up to 10 μm show that, by number, > 97% residues are <1 μm in diameter, the upper limit of the NTA. The range of concentration and distribution properties indicates that insoluble residue properties vary with ambient aerosol concentrations, cloud microphysics, and meteorological dynamics. NTA has great potential for studying the role that insoluble residues play in critical atmospheric processes.

Real-time monitoring of emissions from monoethanolamine-based industrial scale carbon capture facilities

We demonstrate the capabilities and properties of using Proton Transfer Reaction time-of-flight mass spectrometry (PTR-ToF-MS) to real-time monitor gaseous emissions from industrial scale amine-based carbon capture processes. The benchmark monoethanolamine (MEA) was used as an example of amines needing to be monitored from carbon capture facilities, and to describe how the measurements may be influenced by potentially interfering species in CO2 absorber stack discharges. On the basis of known or expected emission compositions, we investigated the PTR-ToF-MS MEA response as a function of sample flow humidity, ammonia, and CO2 abundances, and show that all can exhibit interferences, thus making accurate amine measurements difficult. This warrants a proper sample pretreatment, and we show an example using a dilution with bottled zero air of 1:20 to 1:10 to monitor stack gas concentrations at the CO2 Technology Center Mongstad (TCM), Norway. Observed emissions included many expected chemical species, dominantly ammonia and acetaldehyde, but also two new species previously not reported but emitted in significant quantities. With respect to concerns regarding amine emissions, we show that accurate amine quantifications in the presence of water vapor, ammonia, and CO2 become feasible after proper sample dilution, thus making PTR-ToF-MS a viable technique to monitor future carbon capture facility emissions, without conventional laborious sample pretreatment.

Molecular understanding of sulphuric acid-amine particle nucleation in the atmosphere

Nucleation of aerosol particles from trace atmospheric vapours is thought to provide up to half of global cloud condensation nuclei. Aerosols can cause a net cooling of climate by scattering sunlight and by leading to smaller but more numerous cloud droplets, which makes clouds brighter and extends their lifetimes. Atmospheric aerosols derived from human activities are thought to have compensated for a large fraction of the warming caused by greenhouse gases. However, despite its importance for climate, atmospheric nucleation is poorly understood. Recently, it has been shown that sulphuric acid and ammonia cannot explain particle formation rates observed in the lower atmosphere. It is thought that amines may enhance nucleation, but until now there has been no direct evidence for amine ternary nucleation under atmospheric conditions. Here we use the CLOUD (Cosmics Leaving OUtdoor Droplets) chamber at CERN and find that dimethylamine above three parts per trillion by volume can enhance particle formation rates more than 1,000-fold compared with ammonia, sufficient to account for the particle formation rates observed in the atmosphere. Molecular analysis of the clusters reveals that the faster nucleation is explained by a base-stabilization mechanism involving acid-amine pairs, which strongly decrease evaporation. The ion-induced contribution is generally small, reflecting the high stability of sulphuric acid-dimethylamine clusters and indicating that galactic cosmic rays exert only a small influence on their formation, except at low overall formation rates. Our experimental measurements are well reproduced by a dynamical model based on quantum chemical calculations of binding energies of molecular clusters, without any fitted parameters. These results show that, in regions of the atmosphere near amine sources, both amines and sulphur dioxide should be considered when assessing the impact of anthropogenic activities on particle formation.

Heterogeneous uptake of amines by citric acid and humic acid

Heterogeneous uptake of methylamine (MA), dimethylamine (DMA), and trimethylamine (TMA) onto citric acid and humic acid was investigated using a Knudsen cell reactor coupled to a quadrupole mass spectrometer at 298 K. Acid-base reactions between amines and carboxylic acids were confirmed. The observed uptake coefficients of MA, DMA, and TMA on citric acid at 298 K were measured to be 7.31 ± 1.13 × 10(-3), 6.65 ± 0.49 × 10(-3), and 5.82 ± 0.68 × 10(-3), respectively, and showed independence of sample mass. The observed uptake coefficients of MA, DMA, and TMA on humic acid at 298 K increased linearly with sample mass, and the true uptake coefficients of MA, DMA, and TMA were measured to be 1.26 ± 0.07 × 10(-5), 7.33 ± 0.40 × 10(-6), and 4.75 ± 0.15 × 10(-6), respectively. Citric acid, having stronger acidity, showed a higher reactivity than humic acid for a given amine; while the steric effect of amines was found to govern the reactivity between amines and citric acid or humic acid.