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Gas-phase dimethylamine (DMA) has recently been identified as one of the most important vapors to initiate new particle formation (NPF), even in China's polluted atmosphere. Nevertheless, there remains a fundamental need for understanding the atmospheric life cycle of DMA, particularly in urban areas. Here we pioneered large-scale mobile observations of the DMA concentrations within cities and across two pan-region transects of north-to-south (∼700 km) and west-to-east (∼2000 km) in China. Unexpectedly, DMA concentrations (mean ± 1 σ) in South China with scattered croplands (0.018 ± 0.010 ppbv, 1 ppbv=10−9 L/L) were over three times higher than those in the north with contiguous croplands (0.005 ± 0.001 ppbv), suggesting that nonagricultural activities may be an important source of DMA. Particularly in non-rural regions, incidental pulsed industrial emissions led to some of the highest DMA concentration levels in the world (>2.3 ppbv). Besides, in highly urbanized areas of Shanghai, supported by direct source-emission measurements, the spatial pattern of DMA was generally correlated with population (R 2 = 0.31) due to associated residential emissions rather than vehicular emissions. Chemical transport simulations further show that in the most populated regions of Shanghai, residential DMA emissions can contribute for up to 78% of particle number concentrations. Shanghai is a case study for populous megacities, and the impacts of nonagricultural emissions on local DMA concentration and nucleation are likely similar for other major urban regions globally. [ABSTRACT FROM AUTHOR]

Spatiotemporal heterogeneities in the concentrations of alkaline gases and their particulate counterparts in the marine atmosphere over China's marginal seas were investigated in terms of causes and chemical conversion during two winter cruise campaigns, using semi-continuous measurements made by an onboard URG-9000D Ambient Ion Monitor-Ion Chromatograph (AIM-IC, Thermo Fisher). During the cruise campaign over the East China Sea from 27 December 2019 to 6 January 2020, the concentrations of gas-phase atmospheric trimethylamine (TMA gas) varied by approximately 1 order of magnitude, with an average (± standard deviation) of 0.10±0.04 µ g m -3 corresponding to a mixing ratio of 26±17 pptv. Corresponding mean values were 0.037±0.011 µ g m -3 (14±5 pptv in mixing ratio) over the Yellow Sea during the period from 7 to 16 January 2020 and 0.031±0.009 µ g m -3 (12±4 pptv in mixing ratio) over the Yellow Sea and Bohai Sea from 9 to 22 December 2019. By contrast, the simultaneously observed concentrations of TMA in PM 2.5 , detected as TMAH + , over the East China Sea were 0.098±0.069 µ g m -3 and substantially smaller than the 0.28±0.18 µ g m -3 observed over the Yellow Sea and Bohai Sea from 9 to 22 December 2019. A significant correlation between TMA gas and particulate TMAH + was observed over the East China Sea, but no correlation was found over the Yellow Sea and Bohai Sea. Proportional or disproportional variations in concentrations of TMA gas with particulate TMAH + over the sea zones were probably attributed to the difference in the enrichment of TMAH + in the sea surface microlayer. In addition, spatiotemporal heterogeneities in concentrations of atmospheric ammonia (NH 3gas), atmospheric dimethylamine (DMA gas), and DMA in PM 2.5 , detected as DMAH + , were investigated. Case analyses were performed to illustrate the formation and chemical conversion of particulate aminium ions in marine aerosols. Finally, we hypothesized the release of basic gases and particulate counterparts from the ocean to the atmosphere, together with the secondary formation of DMAH + and chemical conversion of TMAH + , in the marine atmosphere. [ABSTRACT FROM AUTHOR]

To study sea-derived gaseous amines, ammonia, and primary particulate aminium ions in the marine atmosphere of China's marginal seas, an onboard URG-9000D Ambient Ion Monitor-Ion Chromatograph (AIM-IC, Thermo Fisher) was set up on the front deck of the R/V Dongfanghong-3 to semi-continuously measure the spatiotemporal variations in the concentrations of atmospheric trimethylamine (TMA gas), dimethylamine (DMA gas), and ammonia (NH3gas) along with their particulate matter (PM 2.5) counterparts. In this study, we differentiated marine emissions of the gas species from continental transport using data obtained from 9 to 22 December 2019 during the cruise over the Yellow and Bohai seas, facilitated by additional short-term measurements collected at a coastal site near the Yellow Sea during the summer, fall, and winter of 2019. The data obtained from the cruise and coastal sites demonstrated that the observed TMA gas and protonated trimethylamine (TMAH +) in PM 2.5 over the Yellow and Bohai seas overwhelmingly originated from marine sources. During the cruise, no significant correlation (P>0.05) was observed between the simultaneously measured TMAH + and TMA gas concentrations. Additionally, the concentrations of TMAH + in the marine atmosphere varied around 0.28±0.18 µgm-3 (average ± standard deviation), with several episodic hourly average values exceeding 1 µgm-3 , which were approximately 1 order of magnitude larger than those of TMA gas (approximately 0.031±0.009 µgm-3). Moreover, there was a significant negative correlation (P<0.01) between the concentrations of TMAH + and NH4+ in PM 2.5. Therefore, the observed TMAH + in PM 2.5 was overwhelmingly derived from primary sea-spray aerosols. Using TMA gas and TMAH + in PM 2.5 as tracers for sea-derived basic gases and sea-spray particulate aminium ions, the values of non-sea-derived DMA gas , NH3gas , and non-sea-spray particulate DMAH + in PM 2.5 were estimated. The estimated average values of each species contributed 16 %, 34 %, and 65 % of the observed average concentrations for non-sea-derived DMA gas , NH3gas , and non-sea-spray particulate DMAH + in PM 2.5 , respectively. Uncertainties remained in the estimations, as TMAH + may decompose into smaller molecules in seawater to varying extents. The non-sea-derived gases and non-sea-spray particulate DMAH + likely originated from long-range transport from the upwind continents based on the recorded offshore winds and increased concentrations of non-sea-salt SO42- (nss- SO42-) and NH4+ in PM 2.5. The lack of a detectable increase in particulate DMAH + , NH4+ , and nss- SO42- concentrations in several SO2 plumes did not support the secondary formation of particulate DMAH + in the marine atmosphere. [ABSTRACT FROM AUTHOR]

Amines are important for new particle formation and subsequent growth in the atmosphere. Consequently, the processes involved are receiving more attention in recent years. Here, we conduct a field observation in order to investigate the atmospheric particulate amines at a background site in the Yangtze River Delta (YRD) during the summer of 2018. Four amines in PM2.5, i.e., methylamine (MA), dimethylamine (DMA), diethylamine (DEA), and trimethylamine (TMA), were collected, twice daily and analyzed. During the campaign, our measurements found the concentrations of MA, DMA, DEA, and TMA of 15.0 ± 15.0, 6.3 ± 6.9, 20.4 ± 30.1, and 4.0 ± 5.9 ng m−3, respectively, and the four amines correlated well with each other. The concentration of amines appear to be independent of whether they were collected during the day or night. Both MA and DMA exhibited a bimodal size distribution that had peaks at 0.67 and 1.1 µm, suggesting amines preferably distribute on submicron particles. Boundary layer height (BLH), relative humidity, and pH of aerosols were found have a negative relationship with amines, while aerosol liquid water content (ALWC) was found to have a positive relationship with amines. The PMF (positive matrix factorization) source apportionment results showed that the main source of amines in Chongming Island was of anthropogenic origin such as industrial and biomass emission, followed by marine sources including sea salt and marine biogenic sources. Given that the YRD region is still suffering from complex atmospheric pollution and that the knowledge on aerosol amines is still limited, more field studies are in urgent need for a better understanding of the pollution characteristics of amines. [ABSTRACT FROM AUTHOR]

Sulfuric acid (SA)‐dimethylamine (DMA)‐H2O cluster formation has been proven to be responsible for a significant part of new particle formation (NPF) in a Chinese megacity. However, the possible involvement of common atmospheric acids in the subsequent growth of SA‐DMA clusters remains elusive. We simulated formation and growth of clusters using atmospheric relevant concentrations of SA, DMA, and trifluoroacetic acid (TFA), a commonly observed atmospheric perfluorocarboxylic acid, using Density Functional Theory combined with Atmospheric Cluster Dynamics Code. The presence of TFA leads to complex cluster formation routes and an enhancement of NPF rates by up to 2.3 ([TFA] = 5.0 × 106 molecules cm−3, [SA] = 1.0 × 106 molecules cm−3, and [DMA] = 1.5 × 109 molecules cm−3). The agreement of (SA)1·(DMA)1‐2·(TFA)1 concentrations between simulations and ambient measurements during NPF events validates model predictions and implies that perfluorocarboxylic acids could potentially boost atmospheric SA‐DMA NPF rates. Plain Language Summary: Atmospheric nucleation is the earliest step to form new aerosol particles, which includes a complex transformation from gaseous molecules to small clusters, then to critical clusters, and finally to freshly nucleated nanoparticles. Sulfuric acid and dimethylamine have been proved to explain atmospheric nucleation events in urban China. However, whether other atmospheric acidic species could participate in this nucleation process remains elusive. Herein, we report a sulfuric acid‐dimethylamine based nucleation mechanism with the participation of trifluoroacetic acid, a commonly observed strong acid in the atmosphere, using theoretical calculation methods. The model predictions are then validated by ambient measurements in urban Shanghai. Our results suggest that perfluorocarboxylic acids could potentially boost the formation of nanoparticles. Key Points: Theoretical simulations indicate complex atmospheric new particle formation mechanisms involving sulfuric acid, dimethylamine, and trifluoroacetic acidGood agreement of key cluster concentrations between simulations and ambient measurements during new particle formation events is obtainedTrifluoroacetic acid can participate in the growth of sulfuric acid‐dimethylamine clusters and enhance the nucleation rates [ABSTRACT FROM AUTHOR]

Abstract Amines play an important role in the formation and transformation of atmospheric aerosols. Gaseous phase and PM 2.5 samples were collected simultaneously at Nanling Mountains, southern China during autumn 2016 and summer 2017. The site is strongly affected by long distance transport from marine and continental air masses. Five amines, methylamine (MA), dimethylamine (DMA), diethylamine (DEA), dibutylamine (DBA) and morpholine (MOR), were detected by gas chromatography-mass spectrometry (GC-MS) after derivatization. The backward trajectory analyses suggested that different origins of air masses led to seasonal variation of amines. In gaseous phase samples, the average concentrations of total measured amines (Ʃamines) were 193.4 ± 111.7 ng m−3 in autumn 2016 and 307.5 ± 196.7 ng m−3 in summer 2017. In PM 2.5 samples, the average concentrations of Ʃamines were 12.4 ± 10.8 ng m−3 in autumn 2016 and 20.7 ± 11.0 ng m−3 in summer 2017. MA and DMA were the dominant amines, together contributing approximately 70% to gaseous amines and 80% to particulate amines. A strong linear relationship was found between Ʃamines and NO 3 − in PM 2.5 , implying that amines might mainly exist in the form of aminium nitrate. Ammonium (NH 4 +) was found mostly likely in the form of ammonia sulfate. Approximately 7.4% of the gaseous total amines partitioned to PM 2.5. A good linear relationship between the fraction of total atmospheric concentration sorbed by PM 2.5 (Φ) and the concentrations of O 3 was found, suggesting that O 3 likely played an important factor in the gas-to-particle partitioning of amines. Additionally, under high relative humidity circumstances (92% ± 7.0%), direct dissolution was a crucial step for gaseous amines partitioning into particles. The ratios of amines-C to water-soluble organic carbon (WSOC) and amines-N to water-soluble organic nitrogen (WSON) were 0.21% and 1.57% in autumn 2016 and 0.54% and 2.08% in summer 2017, respectively. The results of this study provide essential information on the formation mechanism of particulate amines. Highlights • Gaseous and particulate amines were detected simultaneously at a remote mountain site in southern China. • Amines were mostly likely in the form of aminium nitrate. • Approximately 7.4% of the total gaseous amines partitioned into the particulate phase. • Direct dissolution was a crucial step for gas-to-particle partitioning under high relative humidity circumstances. [ABSTRACT FROM AUTHOR]

Atmospheric amines have attracted increasing attention due to their significant impact on new particle formation, particle hygroscopicity and particle optical properties. In this study, four low-molecule-weight amines were detected from PM 2.5 filter samples collected at an urban site of Pearl River Delta (PRD) region of China in 2018 autumn. During the campaign, the mass concentrations of ambient particulate methylamine (MA, CH 3 NH 2), dimethylamine (DMA, (CH 3) 2 NH), trimethylamine (TMA, (CH 3) 3 N), and diethylamine (DEA, (C 2 H 5) 2 NH) were quantified at daily or 12-h resolution using an optimized Ion Chromatograph (IC) method. The total measured amine concentration was 297 ± 209 ng/m3, which can account for 0.76 ± 0.33% of PM 2.5 mass concentrations. The particulate amines in PRD urban area were dominated by MA (243 ± 179 ng/m3), accounting for over 80% of total amines, then followed by DMA (49 ± 30 ng/m3, 16.5%), TMA (4 ± 2 ng/m3) and DEA (1 ± 1 ng/m3). Based on the correlation analysis, MA and DMA mainly presented as nitrate and sulfate salts. We speculate the amines tend to react with gas-phase HNO 3 or particle-phase nitrate to form particulate amine salts via local process in Guangzhou. As the relative humidity (RH) increased, enhanced partitioning of amine towards the particle phase was observed. Using approach of multiple linear regression, 71% of the particulate amines in PRD urban site could be explained by acid-base process and the rest by primary emissions from combustion sources (29%). • Particulate amines in urban PRD were quantified using an optimized IC method. • Methylamine was the most abundant amine, followed by dimethylamine. • Methylamine and dimethylamine mainly presented as nitrate and sulfate salts. • Enhanced RH facilitated the partitioning of amine towards particle phase. • Acid-base process dominated the amine formation, the left by combustion source. [ABSTRACT FROM AUTHOR]

The newly developed Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus PTR-TOF) is able to simultaneously detect hundreds of gaseous compounds including a big fraction of volatile organic compounds (VOCs) with outstanding mass resolution and sensitivity. Here, we present an application of Vocus PTR-TOF to monitor gaseous dimethylamine (DMA). The sensitivity towards DMA was improved by tuning the voltage settings of the segmented quadrupole following the molecular ion reactor to obtain a suitable ion transmission window. With the assistance of a permeation tube calibration method, the sensitivity of Vocus PTR-TOF for DMA detection was 2.68 cps pptv−1 at a TOF extraction frequency of 16 kHz and the detection limit was 1.44 pptv at 3σ of the background signal for a 1 min integration time. Laboratory experiments at a series of controlled relative humidity (RH) show that RH of the sample had little influences on the measurement of DMA. Vocus PTR-TOF with this hardware setup was deployed from December 2018 to January 2019 at Wangdu, Hebei Province, China. The temporal profile of C 2 -amines with a high time resolution was obtained, while the detection of VOCs remained successful. Such simultaneous measurements of these compounds are meaningful as these compounds are all relevant to aerosol nucleation and growth. Our results indicate that Vocus PTR-TOF can be a powerful tool in both field and laboratory studies for new particle formation research. [ABSTRACT FROM AUTHOR]