Mapping gaseous amines, ammonia, and their particulate counterparts in marine atmospheres of China’s marginal seas: Part 2-spatiotemporal heterogeneity, causes and hypothesis

Mapping gaseous amines, ammonia, and their particulate counterparts in marine atmospheres of China’s marginal seas: Part 2 spatiotemporal heterogeneity, causes and hypothesis Yating Gao, Dihui Chen, Yanjie Shen, Yang Gao, Huiwang Gao, Xiaohong 5 Yao Key Laboratory of Marine Environment and Ecology, and Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ministry of Education, Ocean University of China, Qingdao 266100, China Laboratory for Marine Ecology and Environmental Science, Qingdao National Laboratory for Marine 10 Science and Technology, Qingdao 266237, China

to collect atmospheric particles with 50% aerodynamic cut-off diameters of 11, 7.0, 4.7, 3.3, 2.1, 1.1, 0.65, and 0.43 m. Details of the sampling and chemical analyses can be found in Hu et al. (2015). The cruise campaign was referred to as Campaign C in this study, and the sea zones collected from the three aerosol samples are shown in Figure S1c. Corresponding average values were 0.100.04 µg m -3 (2617 pptv in mixing ratio).

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The values largely decreased to 0.0370.011 µg m -3 (145 pptv in mixing ratio) over the Yellow Sea on 7-16 January 2020. The latter concentrations were comparable to those of 0.031±0.009 μg m -3 (124 pptv in mixing ratio) observed over the Yellow Sea and the Bohai Sea during Campaign A (Chen et al., 2021). Based on the evidence provided below, the observed TMAgas during the period of Campaign B was probably determined by the actual time emission potentials of TMAgas from the cruise sea zone.

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Long-range continental transport should be a negligible contributor to the observed TMAgas in the marine atmosphere.
A moderately good exponential correlation, (TMAgas=0.03e 0.08T ; R 2 =0.76, P<0.01), was demonstrated between the concentrations of TMAgas and ambient air temperature (Fig. 2a)  emissions simultaneously with TMAgas. Thus, we conclude that the seas were the net source of DMAgas and NH3gas during the study. Note that the observed ratios of TMAgas to NH3gas were two orders of magnitude larger than those previously reported in marine atmospheres and adopted for modeling (Van Neste, et al., 1987;Gibb et al., 1999;Yu and Luo, 2014). However, the observed ratios of DMAgas to NH3gas were reasonably comparable to values previously reported (Yu and Luo, 2014). m -3 at 05:00-06:59 on 4 January 2020 (Fig. 1b). The concentrations of TMAH + exhibited a moderately good correlation with those of TMAgas simultaneously observed over the East China Sea when the five episodes with concentrations of TMAH + in PM2.5 exceeding 0.2 µg m -3 were excluded for correlation ( Fig. 2c), suggesting that the TMAH + in PM2.5 may also be derived from marine sources. In addition, a 200 broad peak of TMAH + concentrations (PeakTMAH-1 shadowing in Fig. 1b) was observed on 27-30 December 2019, when a negative correlation existed between the concentrations of TMAH + and NH4 + , with R 2 =0.35, and P<0.01. The negative correlation also supported the conclusion that increased concentrations of TMAH + in PM2.5 were driven by enhanced marine emissions rather than continental transport.

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The large increases in concentrations of particulate NH4 + , for example, when its concentration exceed 5 g m -3 , under offshore winds, clearly indicated the continental transport of air pollutants (Figs. 1bc, S1a).
However, when its concentration was below 1 g m -3 , a significant correlation between particulate NH4 + and TMAH + was apparent, with P<0.01 (empty dots Fig. 3a). When five points with concentrations of particulate TMAH + exceeding 0.2 g m -3 were included in the correlation analysis (full dots in Fig. 3a),

2; (e) and (f) same as (a) and (b) except in E-period 3; grey and pink shadowing represent episodes with increasing NH4 + or SO2, respectively; Fig superimposed in (f) show the correlation between TMAH + and DMAH + in six cycling points in (f))
Three episodes were further selected for deeper analyses of the sea-derived alkaline gases and primary particulate counterparts, during which continental transport was likely to have largely decreased. E-265 period 1 started on 23:00 on December 27 to 13:00 on December 30, 2019, when increases in concentrations of sea-derived gases and sea-derived primary TMAH + in PM2.5 were observed. E-period 2 started on 13:00 on January 3 to 18:00 on January 7, 2020, when 1) an episodic increase in the seaderived primary TMAH + in PM2.5 occurred in the absence of a corresponding increase in TMAgas; 2) an increase in the concentration of sea-derived TMAgas was observed without a corresponding increase in The concentrations of TMAH + in PM2.5 during E-periods 1 and 2 were smaller than those during period Because the SML affects all mass transfers between the atmosphere and ocean (Cunliffe et al., 2013;Quinn, et al., 2015), the release of sea-spray aerosols containing TMAH + should be affected by the abundance of TMAH + in SML, in addition to sea surface wind speeds and concentrations of TMAH + in bulk surface seawater. Combining the observational facts mentioned above, we argue that TMAH + may primary sea-spray aerosols may contain substantially low concentrations of particulate DMAH + , as mentioned above. In addition, a significant decrease in the concentration of particulate TMAH + was apparent with increasing concentrations of particulate NH4 + and DMAH + , as well as those of SO2 (grey shadowing in Fig. 4a). The unique decrease in particulate TMAH + also occurred in E-period 2 and Eperiod 3 (grey and pink shadowing in Fig. 4d,f), regardless of the simultaneous increase or decrease in 320 concentrations of TMAgas. Secondary chemical reactions likely converted particulate TMAH + to compounds that were undetectable by AIM-IC.
Unlike during E-Period 1, the disproportional release of TMAgas with particulate TMAH + from the seas likely occurred in E-periods 2 and 3. Moreover, a large increase in the concentration of particulate DMAH + was observed simultaneously with a large increase in particulate TMAH + in the six episodes 325 observed over the Yellow Sea (Figure superimposed in Fig. 4f). However, only a small increase in particulate DMAH + was detected for the four episodes observed over the East China Sea (cycled empty triangles in Fig. 4d). This disproportion may also be ascribed to the spatiotemporal heterogeneity of enrichments of TMAH + and DMAH + in the SML.
When the values of Kb were used to calculate the effective Henry's Law constants for DMA ( eff KDMA),  (Hu et al., 2015), were included in the analysis. The sample collection sea zones are mapped in Figure 5e. The size distributions of particulate TMAH + in mass concentration and molar ratios of TMAH +

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to NH4 + are shown in Figure 5f.
The concentrations of TMAH + generally increased from the bin-size of 7.0-11 m to that of <0.43 m ( Fig. 1f), which were totally different from those of NH4 + , which peaked at 0.65-1.1 m (Figure was superimposed in Fig. S1c). The unique size distributions of particulate TMAH + also implied that the observed TMAH + was overwhelmingly derived from primary sea spray organic aerosols, based on 385 laboratory experimental results and field measurements (Ault et al., 2013;Prather et al., 2013;Hu et al., 2015Hu et al., , 2018Quinn et al., 2015). Note that mass concentration size distribution patterns of particulate TMAH + were reported similar to those of NH4 + when secondary-formed particulate TMAH + dominated the primary particulate TMAH + (Hu et al., 2018;Xie et al., 2018).
The ratios of TMAH + to NH4 + in bins of different sizes were also calculated. Assuming 1) gas-aerosol 390 equilibria had been achieved and particulate TMAH + to NH4 + co-existed internally, the ratios in differentsized particles should theoretically approach a constant. However, the ratios in particle size bins were distributed across two different ranges, namely 0.2-0.3 and 0.01-0.05, corresponding to concentrations of NH4 + exceeding 0.9 µg m -3 , or below 0.6 µg m -3 , respectively, rejecting the null hypothesis. Note that the ratios were not calculated in size bins when the concentrations of NH4 + were smaller than 0.1 µg m -395 3 . At such low concentrations, the analytic errors may be large and can be transferred to the calculated ratios.
The time series of ratios of DMAgas to NH3gas, particulate DMAH + to particulate NH4 + , and their correlations during Campaign A and B are shown Figure S3a Based on the exponential correlation between basic gases and ambient temperature, we inferred that surface seawater temperature was likely one of the key factors controlling the release of TMAgas, DMAgas, and NH3gas from the seas to the atmosphere. The disproportional release of alkaline gases and 430 corresponding particulate counterparts implied that the enrichment of TMAH + and DMAH + in the SML may be overwhelmingly determined by the release of particulate TMAH + and DMAH + , although the extent of enrichment may be largely affected by surface seawater temperature. Combining no correlation between the molar ratios of TMAH + to NH4 + in PM2.5, the ratios of TMAgas over NH3gas, and the data with substantially larger ratios of TMAH + to NH4 + compared to those of TMAgas to NH3gas, it can be inferred that the observed TMAH + in the marine atmospheres were probably overwhelmed by primary sea spray organic aerosols, and existed mainly in either organic phase or mixed 440 phase. Secondary reactions in the marine atmosphere further led to the conversion of TMAH + as chemicals undetectable by AIM-IC, rather than forming new detectable particulate TMAH + .
The sea-derived DMAgas and NH3gas were expected to exhibit an equilibrium with aerosols containing NH4 + and DMAH + from continental transport, but the equilibria were seemingly not achieved over the three seas. Thermodynamic models, including gas, aqueous phase, organic phase, and mixed phase, are In addition, primary particulate TMAH + and DMAH + were distributed mainly in submicron atmospheric particles. Their concentrations generally increased with decreasing particle size. In contrast, the size 455 distribution of secondary particulate DMAH + should be similar to that of particulate NH4 + (Xie et al., 2018;Hu et al., 2018). Considering the largely increased ratios of TMAH + to NH4 + in <0.43 µm particles, the particles containing TMAH + may yield contributions comparable with anthropogenic particles to cloud condensation nuclei in less polluted marine atmospheres over the China Marginal Sea.
Data availability. The data of this paper are available upon request (contact: Xiaohong Yao,