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New particle formation (NPF) and subsequent particle growth are important sources of condensation nuclei (CN) and cloud condensation nuclei (CCN). While a number of observations have shown positive contributions of NPF to CCN at low supersaturation, negative NPF contributions were often simulated. Using the observations in a typical coastal city of Qingdao, we thoroughly evaluate the simulated number concentrations of CN and CCN using a NPF-explicit parameterization embedded in WRF-Chem model. In terms of CN, the initial simulation shows large biases of particle number concentrations at 10–40 nm (CN10–40) and 40–100 nm (CN40–100). By adjusting the process of gas-particle partitioning, including mass accommodation coefficient of sulfuric acid, the phase changes of primary organic aerosol emissions and the condensational amount of nitric acid, the concomitant improvement of the particle growth process yields a substantial reduction of overestimates of CN10–40 and CN40–100. Regarding CCN, SOA formed from the oxidation of semi-volatile and intermediate volatility organic vapors (SI-SOA) yield is an important contributor. In the original WRF-Chem model with 20 size bins setting, the yield of SI-SOA is too high without considering the differences in oxidation rates of the precursors. Lowering the SI-SOA yield results in much improved simulations of the observed CCN concentrations. On the basis of the bias-corrected model, we find substantial positive contributions of NPF to CCN at low supersaturation (~0.2 %) in Qingdao and over the broad areas of China, primarily due to the competing effects of increasing particle hygroscopicity surpassing that of particle size decrease. This study highlights the potentially much larger NPF contributions to CCN on a regional and even global basis.

This study employed multiple techniques to investigate the contribution of grown new particles to the number concentration of cloud condensation nuclei (CCN) at various supersaturation (SS) levels at a rural mountain site in North China Plain from 29 June to 14 July 2019. On eight new particle formation (NPF) days, the total particle number concentrations (Ncn) were 8.4±6.1 ×103 cm-3, which were substantially higher compared to 4.7±2.6 ×103 cm-3 on non-NPF days. However, the Nccn at 0.2 %SS and 0.4 %SS on the NPF days were significantly lower than those observed on non-NPF days (P

Because anthropogenic sulfur dioxide (SO2) emissions have decreased considerably in the last decade, PM2.5 pollution in China has been alleviated to some extent. However, the effects of reduced SO2 on the particle number concentrations and subsequent contributions of grown new particles to cloud condensation nuclei (CCN) populations, particularly at high altitudes with low aerosol number loadings, are poorly understood. In contrast, the increase in provincial forest areas in China with rapid afforestation over the last few decades expectedly increases the biogenic emissions of volatile organic compounds and their oxidized products as nucleating precursors therein. In this study, we evaluated the campaign-based measurements made at the summit of Mt. Tai (1534 m a.s.l.) from 2007 to 2018. With the decrease in SO2 mixing ratios from 15 ± 13 ppb in 2007 to 1.6 ± 1.6 ppb in 2018, the apparent formation rate (FR) of new particles and the net maximum increase in the nucleation-mode particle number concentration (NMINP) in the spring campaign of 2018 was 2- to 3-fold higher than those in the spring campaign of 2007 with almost the same occurrence frequency of new particle formation (NPF) events. In contrast, the campaign-based comparison showed that the occurrence frequency, in which the maximum geometric median diameter of the grown new particles (Dpgmax) was > 50 nm, decreased considerably from 43 %–78 % of the NPF events before 2015 to 50 nm as a CCN threshold size at high supersaturations, the observed net CCN production decreased from 3.7 × 103 cm−3 (on average) in the five campaigns before 2015 to 1.0 × 103 cm−3 (on average) in the two campaigns in 2017–2018. We argue that the increases in the apparent FR and NMINP are mainly determined by the availability of organic precursors that participate in nucleation and initial growth, whereas the decrease in the growth probability is caused by the reduced emissions of anthropogenic precursors. However, large uncertainties still exist because of a lack of data on the chemical composition of these smaller particles.

In this study, a cruise campaign was conducted over marginal seas in China to measure the concentrations of condensation nuclei ( Ncn ), cloud condensation nuclei ( Nccn ) and other pollutants from day of year (DOY) 110 to DOY 135 of 2018. The ship self-emission signals were exhaustively excluded, and the mean values of Nccn during the cruise campaign were found to slightly increase from 3.2 ± 1.1 × 10 3 cm −3 (mean ± standard deviation) at supersaturation (SS) of 0.2 % to 3.9 ± 1.4 × 10 3 cm −3 at SS of 1.0 %, and the mean value for Ncn was 8.1 ± 4.4 × 10 3 cm −3 . Data analysis showed that marine traffic emissions apparently largely contributed to the increase in Ncn in the daytime, especially in the marine atmospheres over heavily traveled sea zones; however, the fresh sources made no clear contribution to the increase in Nccn . This finding was supported by the quantitative relations between Ncn and Nccn at SS = 0.2 %–1.0 % against the mixing ratios of SO2 in the ship self-emission plumes – i.e., a 1 ppb increase in SO2 corresponded to a 1.4×104 cm −3 increase in Ncn but only a 30–170 cm −3 increase in Nccn , possibly because of abundant organics in the aerosols. Smooth growth can be observed in the marine-traffic-derived particles, reflecting aerosol aging. The estimated hygroscopicity parameter ( κ ) values were generally as high as 0.46–0.55 under the dominant onshore winds, suggesting that inorganic ammonium aerosols likely acted as the major contributor to Nccn largely through aerosol aging processes of decomposing organics. Moreover, the influences of the new transported particles from the continent on the Ncn and Nccn in the marine atmosphere were investigated.

In this study, 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, Thermofisher). During the cruise campaign over the East China Sea on December 27, 2019–January 6, 2020, the concentrations of atmospheric trimethylamine (TMAgas) varied by approximately one order of magnitude, with an average (±standard deviation) of 0.10 ± 0.04 µg m−3. Corresponding means were 0.037 ± 0.011 µg m−3 over the Yellow Sea on 7–16 January 2020 and 0.031 ± 0.009 μg m−3 over the Yellow Sea and the Bohai Sea on 9–22 December 2019. In contrast, the simultaneously observed concentrations of TMA in PM2.5, detected as TMAH+, over the East China Sea were 0.098 ± 0.068 µg m−3 and substantially smaller than 0.28 ± 0.18 μg m−3 over the Yellow Sea and the Bohai Sea on 9–22 December 2019. A significant correlation between TMAgas and particulate TMAH+ was obtained over the East China Sea, but no correlation existed over the Yellow Sea and Bohai Sea. The proportional or disproportional variations in concentrations of TMAgas with particulate TMAH+ over the sea zones were likely attributed to the difference in enrichment of TMAH+ in the sea surface microlayer. In addition, spatiotemporal heterogeneities in concentrations of atmospheric ammonia (NH3gas), atmospheric dimethylamine (DMAgas), and DMA in PM2.5, detected as DMAH+, were also investigated. Case analyses were performed to illustrate the formation and chemical conversion of particulate aminium ions in marine aerosols. Finally, we hypothesized a release of basic gases and particulate counterparts from the ocean to the atmosphere, together with secondary formation of DMAH+ and chemical conversion of TMAH+, in the marine atmosphere.

To study sea-derived gaseous amines, ammonia, and primary particulate aminium ions in the marine atmospheres of China's marginal seas, an onboard URG-9000D Ambient Ion Monitor-Ion chromatography (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 (TMAgas), dimethylamine (DMAgas), and ammonia (NH3gas) along with their particulate matter (PM2.5) counterparts. In this study, we differentiated marine emissions of the gas species originating from continental transport using data obtained from December 9 to 22, 2019 during the cruise over the Yellow and Bohai Seas, facilitated by additional measurements collected at a coastal site near the Yellow Sea during summer 2019. The data obtained during the cruise and the coastal site demonstrated that the observed TMAgas and protonated trimethylamine (TMAH+) in PM2.5 over the Yellow and Bohai Seas overwhelmingly originated from marine sources. During the cruise, there was no significant correlation (P > 0.05) between the simultaneously measured TMAH+ and TMAgas concentrations. Additionally, the concentrations of TMAH+ in the marine atmosphere varied around 0.28 ± 0.18 μg m−3 (average ± standard deviation), with several episodic hourly average values exceeding 1 μg m−3, which were approximately one order of magnitude larger than those of TMAgas (approximately 0.031 ± 0.009 μg m−3). Moreover, there was a significant negative correlation (P

Determination of the updated concentrations of atmospheric particles ( Ncn ) and the concentrations of cloud condensation nuclei ( Nccn ) over the northwestern Pacific Ocean (NWPO) are important to accurately evaluate the influence of aerosol outflow from the Asian continent on the climate by considering the rapid changes in emissions of air pollutants therein. However, field observations in the last two decades are scarce. We conducted a cruise campaign over the NWPO to simultaneously measure Ncn , Nccn and the size distribution of aerosol particles from day of year (DOY) 81 to DOY 108 of 2014. The mean values of Nccn at supersaturation (SS) of levels 0.2 % and 0.4 % were 0.68 ± 0.38 × 10 3 and 1.1 ± 0.67 × 10 3 cm −3 , respectively, with an average of 2.8 ± 1.0 × 10 3 cm −3 for Ncn during the cruise over the NWPO. All are approximately 1 order of magnitude larger than spring observations made during the preceding two decades in the remote marine atmosphere. The larger values, against the marine natural background reported in the literature, imply an overwhelming contribution from continental inputs. The calculated activity ratios (ARs) of the cloud condensation nuclei (CCN) were 0.30±0.11 and 0.46±0.19 at SS levels of 0.2 % and 0.4 %, respectively, which are almost the same as those of upwind semi-urban sites. High Nccn and CCN activities were observed from DOY 98 to DOY 102, when the oceanic zone received even stronger continental input. Excluding biomass burning (BB) and dust aerosols, good correlation between Nccn at 0.4 % SS and the number concentrations of > 60 nm particles ( N>60 nm ) was obtained during the entire cruise period, with a slope of 0.98 and R2=0.94 , and the corresponding effective hygroscopicity parameter ( κ ) was estimated to be 0.40. A bimodal size distribution pattern of the particle number concentration was generally observed during the entire campaign when the N>90 nm varied largely. However, the N , accounting for approximately one-third of the total number concentration, varied narrowly, and two NPF events associated with vertical transport were observed. This implies that a pool of nucleation-mode atmospheric particles is aloft. BB and dust events were observed over the NWPO, but their aerosol contributions to Ncn and Nccn were minor (i.e., 10 % or less) on a monthly timescale.

In this study, a methodology for satellite retrieval of cloud condensation nuclei (CCN) in shallow marine boundary layer clouds is presented and validated. This methodology is based on retrieving cloud base drop concentration (Nd) and updrafts (Wb), which are used for calculating supersaturation (S). The Nd is the activated CCN concentration in clouds at a given S. The accuracy of the satellite retrieval is validated against the surface-measured CCN of a cruise campaign over the heavily polluted northwest Pacific Ocean. Clouds which are coupled with the sea surface have good agreement between satellite retrieved Nd and surface-measured CCN after performing corrections for temperature and adiabatic fraction. This study broadens the applicability of the methodology from aerosol-limited to contaminated regions. The validation shows ±30% accuracy in retrieving CCN of both clean and polluted regions. The results further demonstrate the strong dependence of marine shallow cloud Nd on CCN number concentrations and updraft, which allows us to further apply this methodology to quantify the relationships between CCN and cloud microphysical properties and reduce the uncertainty of radiation forcing caused by aerosol cloud interaction (ACI).

The growth of newly formed particles with diameters from ~ 10 nm to a larger size was investigated in Beijing's urban atmosphere on 10–23 December 2011, 12–27 April 2012 and through June–August 2014. The maximum geometric median diameter (Dpgmax) of newly formed particles in 11/27 new particle formation (NPF) events through June–August exceeded 75 nm, and the grown new particles may contribute to the population of cloud condensation nuclei. In contrast, no apparent growth in new particles with Dpgmax

Amines reportedly overwhelm ammonia in generating new particles through neutralizing sulfuric acid vapor even with several orders smaller concentrations of amines against ammonia in ambient air, demonstrating an attractive prospect in adjusting concentrations of amines to adjust aerosol number loadings, alleviate air pollution and manipulate aerosol cooling effects. Due to lack of in-situ observations, real competition of amines against ammonia in ambient air to be neutralized by acids remains poorly understood. Here, successful semi-continuous measurements of gaseous amines and ammonia and their particulate partners in marine atmospheres reveal that atmospheric trimethylamine (TMAgas) unable to compete with NH3gas and to form particulate trimethylaminium (TMAH+), but the particulate TMA (TMAparticulate) is detectable and comparable to TMAgas under NH3gas -3. Contradictory to the common knowledge, the preexisting TMAparticulate is largely depleted in strong SO2 plumes with abundant acids and even depleted NH3gas. A two-aerosol-phase transfer concept model is proposed to interpret the new findings, but no single-phase acid-base neutralization reactions can. In contrast, observational evidences confirm that gaseous dimethylamine (DMAgas) plus particulate dimethylaminium (DMAH+) overwhelmingly exist as DMAH+ under atmospheric NH3 (NH3gas) -3 versus DMAgas under NH3gas >1.8 µg m-3, respectively. The neutralization of DMAgas to form DMAH+ is always enhanced in strong SO2 plumes, almost independent on NH3gas. Thermodynamically, DMAgas may act as a competitor in generating secondary particles only under low NH3gas or in SO2 plumes.

In this study, a cruise campaign was conducted over China marginal seas to measure concentrations of condensation nuclei (Ncn), cloud condensation nuclei (Nccn) and other pollutants during DOY 110 to DOY 135 of 2018. With exhaustedly excluded self-ship emission signals, the mean values of Nccn during the cruise campaign slightly increased from 3.2 ± 1.1 × 103 cm−3 (mean ± standard) at supersaturation (SS) of 0.2 % to 3.9 ± 1.4 × 103 cm−3 at SS of 1.0 %, and the mean value for Ncn was 8.1 ± 4.4 × 103 cm−3. Data analysis showed that marine traffic emissions apparently yielded a large contribution to the increase of Ncn in daytime, especially in marine atmospheres over their heavily travelled sea zones; however, the fresh sources had no clear contribution to the increase of Nccn. This finding was supported by the quantitative relations between Ncn and Nccn at SS = 0.2–1.0 % against mixing ratios of SO2 in self-ship emission plumes, i.e., 1 ppb increase in SO2 corresponds to 1.4 × 104 cm−3 increase in Ncn, but only 30–170 cm−3 increase in Nccn possibly because of abundant organics in the aerosols. The smooth growth of marine traffic derived particles can be observed, reflecting aerosol aging. The estimated hygroscopicity parameter (κ) values were generally as high as 0.46–0.55 under the dominant onshore winds, suggesting inorganic ammonium aerosols likely acting as the major contributor to Nccn through aerosol aging processes largely decomposed organics. Moreover, the influences of the transported new particles from the continent on Ncn and Nccn in the marine atmosphere were also investigated.

The updated concentrations of atmospheric particles (N cn ) and the concentrations of cloud condensation nuclei (N ccn ) over the northwestern Pacific Ocean (NWPO) were important to accurately evaluate the influence of aerosol outflow from the Asian continent on the climate by considering rapid changes in emissions of air pollutants therein. However, field observations were scarce in the last two decades. We conducted a cruise campaign over the NWPO to simultaneously measure N cn , N ccn and the size distribution of aerosol particles from DOY 81 to DOY 108 of 2014. The mean values of N ccn at supersaturation (SS) of 0.2 % and 0.4 % were 0.68 ± 0.38×10 3 cm −3 and 1.1 ± 0.67×10 3 cm −3 , respectively, with an average for Ncn of 2.8 ± 1.0×10 3 cm −3 during the cruise over the NWPO, which were all approximately one order of magnitude larger than spring observations from two decades ago in the atmosphere of remote marine areas. The higher values, against the marine natural background reported in the literature, implied an overwhelming contribution from continental inputs. The calculated CCN activity ratios were 0.30 ± 0.11 and 0.46 ± 0.19 at SS of 0.2 % and 0.4 %, respectively, which were almost the same as those of upwind semi-urban sites. High N ccn and CCN activities were observed from DOY 98 to 102, when the oceanic zone received even stronger continental inputs. During the whole cruise period with the exclusion of biomass burning and dust aerosols, a good correlation between N ccn at 0.4 % SS and the number concentrations of > 60 nm particles (N > 60 nm ), with the slope of 0.98 and R 2 = 0.94, was obtained, and the corresponding effective hygroscopicity parameter ( k ) was estimated as 0.40. The bimodal size distribution pattern of the particle number concentration was generally observed during the entire campaign when the N > 90 nm varied largely. However, the N , accounting for approximately 1 / 3 of the total number concentration, varied narrowly, and two NPF events associated with vertical transport were observed, implying a pool of nucleation mode atmospheric particles aloft. Biomass burning (BB) and dust events were observed over the NWPO, but the contributions of BB and dust aerosols to N cn and N ccn were minor (i.e., 10 % or less) on the monthly time scale.

Interannual variabilities in atmospheric ammonia (NH3) during the most recent 7–11 years were investigated at 14 sites across North America using the monitored data obtained from NAPS, CAPMoN and AMoN networks. The long-term average of atmospheric NH3 ranged from 0.8 to 2.6 ppb, depending on location, at four urban and two rural/agricultural sites in Canada. The annual average at these sites did not show any deceasing trend with largely decreasing anthropogenic NH3 emission. An increasing trend was actually identified from 2003 to 2014 at the downtown Toronto site using either the Mann–Kendall or the ensemble empirical mode decomposition method, but “no” or “stable” trends were identified at other sites. The ∼ 20 % increase during the 11-year period at the site was likely caused by changes in NH4+–NH3 partitioning and/or air–surface exchange process as a result of the decreased sulfur emission and increased ambient temperature. The long-term average from 2008 to 2015 was 1.6–4.9 ppb and 0.3–0.5 ppb at four rural/agricultural and at four remote US sites, respectively. A stable trend in NH3 mixing ratio was identified at one rural/agricultural site while increasing trends were identified at three rural/agricultural (0.6–2.6 ppb, 20–50 % increase from 2008 to 2015) and four remote sites (0.3–0.5 ppb, 100–200 % increase from 2008 to 2015). Increased ambient temperature was identified to be a cause for the increasing trends in NH3 mixing ratio at four out of the seven US sites, but what caused the increasing trends at other US sites needs further investigation.

The cumulative atmospheric nitrogen deposition has been found to profoundly impact the nutrient stoichiometry of the eastern China seas (ECSs: the Yellow Sea and East China Sea) and the northwestern Pacific Ocean (NWPO). In spite of the potential significance of dry deposition in those regions, shipboard observations of atmospheric aerosols remain insufficient, particularly regarding the compositions of water-soluble nitrogen species (nitrate, ammonium and water-soluble organic nitrogen – WSON). We conducted a cruise covering the ECSs and the NWPO during the spring of 2014 and observed three types of atmospheric aerosols. Aluminum content, air mass backward trajectories, weather conditions, and ion stoichiometry allowed us to discern dust aerosol patches and sea-fog-modified aerosols (widespread over the ECSs) from background aerosols (open ocean). Among the three types, sea-fog-modified aerosols contained the highest concentrations of nitrate (536 ± 300 nmol N m−3), ammonium (442 ± 194 nmol N m−3) and WSON (147 ± 171 nmol N m−3); furthermore, ammonium and nitrate together occupied ∼ 65 % of the molar fraction of total ions. The dust aerosols also contained significant amounts of nitrate (100 ± 23 nmol N m−3) and ammonium (138 ± 24 nmol N m−3) which were obviously larger than those in the background aerosols (26 ± 32 for nitrate and 54 ± 45 nmol N m−3 for ammonium), yet this was not the case for WSON. It appeared that dust aerosols had less of a chance to come in contact with WSON during their transport. In the open ocean, we found that sea salt (e.g., Na+, Cl−, Mg2+), as well as WSON, correlated positively with wind speed. Apparently, marine dissolved organic nitrogen (DON) was emitted from breaking waves. Regardless of the variable wind speeds from 0.8 to as high as 18 m s−1, nitrate and ammonium, by contrast, remained in narrow ranges, implying that some supply and consumption processes of nitrate and ammonium were required to maintain such a quasi-static condition. Mean dry deposition of total dissolved nitrogen (TDN) for sea-fog-modified aerosols (1090 ± 671 µmol N m−2 d−1) was 5 times higher than that for dust aerosols (190 ± 41.6 µmol N m−2 d−1) and around 20 times higher than that for background aerosols (56.8 ± 59.1 µmol N m−2 d−1). Apparently, spring sea fog on the ECSs played an important role in removing atmospheric reactive nitrogen from the Chinese mainland and depositing it into the ECSs, thus effectively preventing its seaward export to the NWPO.

A multi-model ensemble of Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) simulations are used to study the atmospheric oxidized nitrogen (NOy) deposition over East Asia under climate and emission changes projected for the future. Both dry and wet NOy deposition shows significant decreases in the 2100s under RCP 4.5 and RCP 8.5, primarily due to large anthropogenic emission reduction over both land and sea. However, in the near future of the 2030s, both dry and wet NOy deposition increases significantly due to continued increase in emissions. The individual effect of climate or emission changes on dry and wet NOy deposition is also investigated. The impact of climate change on dry NOy deposition is relatively minor, but the effect on wet deposition, primarily caused by changes in precipitation, is much higher. For example, over the East China Sea, wet NOy deposition increases significantly in summer due to climate change by the end of this century under RCP 8.5, which may subsequently enhance marine primary production. Over the coastal seas of China, as the transport of NOy from land becomes weaker due to the decrease of anthropogenic emissions, the effect of ship emission and lightning emission becomes more important. On average, seasonal mean total NOy deposition is projected to be enhanced by 24–48 % and 3 %–37 % over Yellow Sea and East China Sea, respectively, by the end of this century. Therefore, continued control of both anthropogenic emission over land and ship emissions may reduce NOy deposition to the Chinese coastal seas.

Utilizing a recent observational particulate matter with diameters less than 2.5 µm (PM2.5) dataset in North China, this study reveals a distinct seesaw feature of abnormally high and low PM2.5 concentrations in the adjacent two months of December 2015 and January 2016, accompanied by distinct meteorological modulations. The seesaw pattern is postulated to be linked to super El Niño and the Arctic Oscillation (AO). During the mature phase of El Niño in December 2015, the weakened East Asian Winter Monsoon (EAWM) and the associated low-level southerly wind anomaly reduced planetary boundary layer height, favoring strong haze formation. This circulation pattern was completely reversed in the following month, in part due to a sudden phase change of the AO from positive to negative and the beginning of a decay of the El Niño, which enhanced the southward shift of the upper-tropospheric jet from December to January relative to climatology, leading to an enhanced EAWM and substantially lower haze formation. This sub-seasonal change in circulation is also robustly found in 1982/1983 and 1997/1998, implicative of a general physical mechanism dynamically linked to El Niño and the AO. Numerical experiments with the Weather Research and Forecasting (WRF)-Community Multi-scale Air Quality (CMAQ) model were used to test the modulation of the meteorological conditions on haze formation. With the same emission, simulations for three super El Niño periods (1983, 1997 and 2015) robustly show higher PM2.5 concentrations under the mature phase of the super El Niño, but substantially lower PM2.5 concentrations during the decay phase of El Niño (and the sudden AO phase change), further verifying the modulation effect of sub-seasonal circulation anomaly on PM2.5 concentrations in North China.

To study the particle number concentration, size distribution and new particle formation (NPF) events in marine atmosphere, we made measurements during six cruise campaigns over the marginal seas of China in 2011–2016 and one campaign from the marginal seas to the Northwest Pacific Ocean (NWPO) in 2014. We observed relatively frequent NPF events in the atmosphere over the marginal seas of China, i.e., 23 out of 126 observational days with the highest occurrence frequency in fall, followed by spring and summer. 22 out of 23 NPF events were analyzed to be associated with the long-range transport of continental pollutants based on 24-hr air mass back trajectories and the preexisting particle number concentrations largely exceeding the clean marine background, leaving one much weaker NPF event to be likely induced by oceanic precursors alone and supported by multiple independent evidences. Although the long-range transport signal of continental pollutants can be clearly observed in the remote marine atmosphere over the NWPO, NPF events were observed only in 2 days out of 36 days. The nucleation mode particles ( 30 nm), however, accounted for as high as 40 % p 13 % of the total particle number concentration during the NWPO cruise campaign, implying that there were many undetected NPF events in the sea-level atmosphere or above. To better characterize NPF events, we introduced a term, i.e., the net maximum increase in nucleation mode particles number concentration (NMINP) and correlated it with formation rate of new particles (FR). We found a moderately good linear correlation between NMINP and FR at FR ≤ 8 cm −3 s −1 , but there was no correlation at FR > 8 cm −3 s −1 . The possible mechanisms were argued in terms of roles of different vapor precursors. We also found a ceiling existing for the growth of new particles from 10 nm to larger size in most of NPF events. We thereby introduce a term, i.e., the maximum geometric median diameter of new particles (D pgmax ) and correlate it with the growth rate of new particles (GR). A moderately good linear correlation was also obtained between D pgmax and GR, and only GR larger than 7.9 nm h −1 can lead to new particles growing with D pgmax beyond 50 nm. Combining simultaneous measurements of the particle number size distributions and cloud condensation nuclei (CCN) at different super saturations (SS), we indeed observed a clear increase in CCN when the D pg of new particles exceeded 50 nm at SS = 0.4 %. However, it was not the case for SS = 0.2 %. Consistent with previous studies in continental atmosphere, our results implied that 50 nm can be used as the threshold for new particles to be activated as CCN in the marine atmosphere. Moreover, the κ decreased from 0.4 to 0.1 during the growth period of new particles, implying that organics likely overwhelmed the growth of new particle to CCN size. The chemical analysis of nano-MOUDI samples revealed TMA and oxalic acid may play the important role in the growth of new particles.

A bell-shape vertical profile of chlorophyll a (Chl a) concentration, conventionally referred as Subsurface Chlorophyll Maximum (SCM) phenomenon, has frequently been observed in stratified oceans and lakes. This profile is assumed to be a general Gaussian distribution in this study. By substituting the general Gaussian function into ecosystem dynamical equations, the steady-state solutions for SCM characteristics (i.e. SCM layer depth, thickness, and intensity) in various scenarios are derived. These solutions indicate that: (1) The maximum in Chl a concentrations occurs at or below the depth with the maximum in growth rates of phytoplankton locating at the transition from nutrient limitation to light limitation, and the depth of SCM layer deepens logarithmically with an increase in surface light intensity; (2) The shape of SCM layer (thickness and intensity) is mainly influenced by nutrient supply, but independence of surface light intensity; (3) The intensity of SCM layer is proportional to the diffusive flux of nutrient from below, getting stronger as a result of this layer being shrank by a higher light attenuation coefficient or a larger sinking velocity of phytoplankton. The analytical solutions can be useful to estimate environmental parameters difficultly obtained from on-site observations.

In this study, five on-board microcosm experiments were performed in the subtropical gyre, Kuroshio Extension region of the Northwest Pacific Ocean (NWPO) and the Yellow Sea (YS), in order to investigate phytoplankton growth following the addition of artificially modified mineral dust (AM-dust) and various nutrients (nitrogen – N, phosphorus – P, iron – Fe, N + P, and N + P + Fe). The two experiments carried out with AM-dust addition in the subtropical gyre showed a maximum chlorophyll a (Chl a) concentration increase of 1.7- and 2.8-fold, while the cell abundance of large-sized phytoplankton (> 5 μm) showed a 1.8- and 3.9-fold increase, respectively, relative to the controls. However, in the Kuroshio Extension region and the YS, the increases in maximum Chl a and cell abundance of large-sized phytoplankton following AM-dust addition were at most 1.3-fold and 1.7-fold larger than those in the controls, respectively. A net conversion efficiency index (NCEI) newly proposed in this study, size-fractionated Chl a, and the abundance of large-sized phytoplankton were analysed to determine which nutrients contribute to support phytoplankton growth. Our results demonstrate that a combination of nutrients, NP or NPFe as well as other micro-constituents, are responsible for phytoplankton growth in the subtropical gyre following AM-dust addition. Single nutrient addition, i.e., N in the Kuroshio Extension region and P/N in the YS, controls the phytoplankton growth following AM-dust addition. In the AM-dust-addition experiments, wherein the increased NP or P were identified to determine phytoplankton growth, the dissolved inorganic P from AM-dust (8.6 nmol L−1) was much lower than the theoretically estimated minimum P demand (~ 20 nmol L−1) for phytoplankton growth. These observations suggest that additional supply augments the bioavailable P stock in incubated seawater with AM-dust addition, most likely due to an enhanced solubility of P from AM-dust or re-mineralization of the dissolved organic P.