Large contributions of anthropogenic sources to amines in fine particles at a coastal area in northern China in winter

Characteristics of aerosol aminiums over a coastal city in North China: Insights from the divergent impacts of marine and terrestrial influences

Aminium ions, as crucial alkaline components within fine atmospheric particles, have a notable influence on new particle formation and haze occurrence. Their concentrations within coastal atmosphere depict considerable variation due to the interplay of distinctive marine and terrestrial sources, further complicated by dynamic meteorological conditions. This study conducted a comprehensive examination of aminiums ions concentrations, with a particular focus on methylaminium (MMAH+), dimethylaminium (DMAH+), trimethylaminium (TMAH+), and triethylaminium (TEAH+) within PM2.5, over varying seasons (summer, autumn, and winter of 2019 and summer of 2021), at an urban site in the coastal megacity of Qingdao, Northern China. The investigations revealed that the total concentration of particulate aminium ions (∑Aminium) was 21.6 ± 23.6 ng/m3, exhibiting higher values in the autumn and winter compared to the two summer periods. Considering diurnal variations during autumn and winter, concentrations of particulate aminium ions (excluding TEAH+) exhibited a slight increase during the day compared to night, with a notable peak during the morning hours. However, it was not the case for TEAH+, which was argued to be readily oxidized by ambient oxidants in the afternoon. Additionally, the ∑Aminium within the summer demonstrated markedly elevated levels during the day compared to night, potentially attributed to daytime sea fog associated with sea-land breeze interactions. Positive matrix factorization results indicate terrestrial anthropogenic emissions, including vehicle emission mixed with road dust and primary pollution, as the primary sources of MMAH+ and DMAH+. Conversely, TMAH+ was predominantly emitted from agricultural and marine sources. With the dominance of sea breeze in summer, TMAH+ was identified as a primary marine emission correlated with sea salt, while MMAH+, DMAH+, and TEAH+ were postulated to undergo secondary formation. Furthermore, a notable inverse correlation was observed between TMAH+ and methanesulfonate in PM2.5, consistent with dynamic emissions of sulfur-content and nitrogen-content gases reported in the literature.

Positive matrix factorization of seasonally resolved organic aerosol at three different central European background sites based on nuclear magnetic resonance Aerosolomics data

Concentration data derived from 1H NMR analysis of the water-soluble organic compounds from fine aerosol (PM2.5) at three Central European background stations, Košetice, Frýdlant (both in the Czech Republic), and Melpitz (Germany), were used for detailed source apportionment analysis. Two winter and two summer episodes (year 2021) with higher organic concentrations and similar wind directions were selected for NMR analyses. The concentration profiles of 61 water-soluble organic compounds were determined by NMR Aerosolomics and a principal component analysis (PCA) was performed on this dataset. Based on the PCA results, 23 compounds were selected for positive matrix factorization (PMF) analysis in order to identify dominant aerosol sources at rural background sites in Central Europe. Both the PCA and the subsequent PMF analyses clearly distinguished the characteristics of winter and summer aerosol particles. In summer, four factors were identified from PMF and were associated with biogenic aerosol (61-78 %), background aerosol (9-15 %), industrial biomass combustion (7-13 %), and residential heating (5-13 %). In winter, only 3 factors were identified - industrial biomass combustion (33-49 %), residential heating (37-45 %) and a background aerosol (8-30 %). The main difference was observed in the winter season with a stronger contribution of emissions from industrial biomass burning at the Czech stations Košetice and Frýdlant (47-49 %) compared to the Melpitz station (33 %). However, in general, there were negligible differences in identified sources between stations in the given seasons, indicating a certain homogeneity in PM2.5 composition within Central Europe at least during the sampling periods.

Implications for new particle formation in air of the use of monoethanolamine in carbon capture and storage

Alkanolamines are currently being deployed in carbon capture and storage (CCS) technology worldwide, and atmospheric emissions have been found to coincide with locations exhibiting elevated concentrations of methanesulfonic acid (MSA). It is thus critical to understand the fate and potential atmospheric reactions of these chemicals. This study reports the characterization of sub-10 nm nanoparticles produced through the acid-base reaction between gas phase monoethanolamine (MEA) and MSA, a product of organosulfur compound oxidation in air, using a flow reactor under dry and humid (up to ∼60% RH) conditions. Number size distribution measurements show that MEA is even more efficient than methylamine in forming nanoparticles on reaction with MSA. This is attributed to the fact that the MEA structure contains both an -NH2 and an -OH group that facilitate hydrogen bonding within the clusters, in addition to the electrostatic interactions. Due to this already strong H-bond network, water has a relatively small influence on new particle formation (NPF) and growth in this system, in contrast to MSA reactions with alkylamines. Acid/base molar ratios of unity for 4-12 nm particles were measured using thermal desorption chemical ionization mass spectrometry. The data indicate that reaction of MEA with MSA may dominate NPF under some atmospheric conditions. Thus, the unique characteristics of alkanolamines in NPF must be taken into account for accurate predictions of impacts of CCS on visibility, health and climate.

Comprehensive understanding on sources of high levels of fine particulate nitro-aromatic compounds at a coastal rural area in northern China

Nitro-aromatic compounds (NACs) are among the major components of brown carbon (BrC) in the atmosphere, causing negative impacts on regional climate, air quality, and ecological health. Due to the extensive origins, it is still a challenge to figure out the contributions and originating regions for different sources of atmospheric NACs. Here, field observations on fine particulate NACs were conducted at a coastal rural area in Qingdao, China in the winter of 2018 and 2019. The mean total concentrations of fine particulate nitro-aromatic compounds were 125.0 ± 89.5 and 27.7 ± 21.1 ng/m3 in the winter of 2018 and 2019, respectively. Among the measured eleven NACs, nitrophenols and nitrocatechols were the most abundant species. Variation characteristics and correlation analysis showed that humidity and anthropogenic primary emissions had significant influences on the NAC abundances. In this study, two tracing methods of the improved spatial concentration weighted trajectory (SCWT) model and the receptor model of positive matrix factorization (PMF) were combined to comprehensively understand the origins of NACs in fine particles at coastal Qingdao. Four major sources were identified, including coal combustion, biomass burning, vehicle exhaust, and secondary formation. Surprisingly, coal combustion was responsible for about half of the observed nitro-aromatic compounds, followed by biomass burning (∼30%). The results by SCWT demonstrated that the coal combustion dominated NACs mainly originated from the Shandong peninsula and the areas to the north and southwest, while those dominated by biomass burning primarily came from local Qingdao and the areas to the west.

Alkali metal doped crystalline g-C3N4 with an enriched cyano group for visible-light photocatalytic degradation of methylamine

In this study, alkali-metal-doped crystalline g-C3N4 with an enriched cyano group was synthesized using the molten salt method and used for the visible-light photocatalytic degradation of methylamine (MA), a common organic amine compound with a low odor threshold. Different types and proportions of melting salts (Li, K, and Na) were added during secondary calcination to regulate the morphology, crystallinity, and surface defects of graphitic carbon nitride (g-C3N4). With molten salt treatment matched the melting point of the binary salt system, a cyano group and alkali metal co-doped crystalline g-C3N4 with a high surface area and good crystallinity were prepared. Co-decorating the alkali metal and cyano groups on crystalline g-C3N4 facilitated the adsorption of MA, realized an excellent photo-charge transfer efficiency, and generated more superoxide radicals. Compared with pristine g-C3N4 (PCN), the apparent rate constant of LiK15 : 5-CCN for the degradation of MA increased by 10.2 times and the degradation efficiency of 1000 ppm MA gas was 93.1% after 90 min of irradiation with visible light, whereas the degradation efficiency of PCN was 19.2%.

Geochemical studies of low molecular weight organic acids in the atmosphere: sources, formation pathways, and gas/particle partitioning

Low molecular weight monocarboxylic acids (LMW monoacids, C₁-C₁₀) are the most abundant gaseous organic compound class in the atmosphere. Formic or acetic acid is the dominant volatile organic compound (VOC) in Earth's atmosphere. They can largely contribute to rainwater acidity, especially in the tropical forest, and react with alkaline metals, ammonia, and amines, contributing to new particle formation and secondary organic aerosol production. Gaseous and particulate LMW monoacids were abundantly reported in China. They can be directly emitted from fossil fuel combustion and biomass burring; however, the secondary formation is more important than primary emissions via the photochemical oxidation of anthropogenic and biogenic VOCs. In this paper, we review the distributions of LMW monoacids from urban, mountain, and marine sites as well as from rainwater and alpine snow samples and discuss their sources and formation mechanisms in the atmosphere. We also discuss their importance as cloud condensation nuclei (CCN) and provide future perspectives of LMW monoacids study in the warming world.