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Gaseous amines have recently been identified as the key precursors for frequent new particle formation in polluted urban atmospheres. An open question that arises is why amines are abundant in urban areas despite the absence of agricultural emissions. Here, using the Vocus Proton‐Transfer‐Reaction Time‐of‐Flight Mass‐Spectrometry Mobile Laboratory, we present highly time‐resolved and ultrasensitive measurements of amines to elucidate their atmospheric abundance and source distribution over the Yangtze River Delta city cluster. Our results show strong spatiotemporal heterogeneity in atmospheric C2‐ and C3‐amine levels across various landscapes. Unexpectedly, we found that urban areas were ubiquitous hotspots of amines while amine source strength from agricultural areas were rather low. Corroborated by source measurements and source tracers, all of the evidence suggest that nonagricultural emissions are the most important sources responsible for the observed patterns of urban atmospheric amines, implying significant consequences for the global amine emission inventory. Plain Language Summary: Recently, the cluster formation of sulfuric acid‐dimethylamine‐H2O has been identified as an important mechanism to explain the frequent formation of new particles in urban polluted atmospheres. However, the interest in gaseous amines across the aerosol scientific community contrasts sharply with the extremely sparse information on their sources and atmospheric abundance. In this study, we present the first mobile measurements showing that the source strength of amines from agricultural areas is modest, thus questing the long‐held assumption that the agricultural sources of amines are similar to those of ammonia. In the case of C2 amines, industrial processes are considered to be an important emission pathway. The dominance of nonagricultural sources, such as fuel combustion, in C3 amines is likely to assign these volatile amine compounds a key function in enhancing new particle formation in polluted atmospheres. Key Points: Mobile measurements are a powerful approach to map major sources of gaseous aminesIn highly urbanized areas, nonagricultural emission sources dominate atmospheric aminesC2 and C3 amines are mainly originated from industrial and mobile sources, respectively [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]

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]