Aligning experimental and model perspectives on atmospheric nanoparticle growth

A significant fraction (>50%) of current cloud condensation nuclei (CCN) is estimated to stem from the formation of new particles. But the mechanisms governing new particle formation (NPF) process are still poorly understood, especially regarding preindustrial NPF. In order to investigate preindustrial NPF process and its contribution to CCN budget, intensive ambient observations were carried out between March 28 and June 27, 2022 at the pristine high-altitude Izaña Atmospheric Observatory (IZO; 2367 m a.s.l., 28°18'32.3"N 16°29'58.1"W), which is located on the island of Tenerife, Canary Islands. This site is characterized by clean air and pristine skies with minimal local anthropogenic influence. Among with other instrumentations, a Multi-scheme chemical IONization (MION) inlet coupled to an atmospheric pressure interface time-of-flight mass spectrometer (APi-ToF-MS) was used to measure the molecular composition of neutral vapours including the less oxygenated organic compounds, sulphuric acid (SA), methane sulfonic acid (MSA), and highly oxygenated organic molecules (HOM) via the fast switching of two reagent ion schemes (Br- and NO3-). A Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF) was deployed to measure the potential precursor volatile organic compounds (VOC), dimethylsulphide (DMS) and their oxidation products. Filter samples were collected and analyzed in the laboratory with a filter inlet for gases and aerosols coupled to a high-resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-TOF-CIMS), yielding the molecular composition of particulate organics. During the measurement period, clustering events were frequently observed, particularly in May and June. NPF precursors, e.g., SA and HOM, were also substantially higher in May and June, indicating their potential role in the NPF process. This is also consistent with the time series of their precursors such as DMS, SO2, and terpenes. NPF events in the presence of Sahara dust events were also observed, exhibiting lower levels of organics in the particle phase compared to clear NPF events. In addition, higher levels of marine MSA and SA were observed on some nights, potentially resulting from the updraft and transport from the Atlantic Ocean to the marine free troposphere. The measurements at IZO station provide us with a valuable dataset regarding NPF at this pristine high-altitude location with marine and Sahara dust influences. Chemical characterization of the freshly formed clusters will increase our understanding of the nucleation mechanism responsible for preindustrial NPF, as well as free tropospheric chemistry. Our study will also provide new insights on a molecular basis to better understand present and future aerosols, and their effects on air quality and climate.

Abstract. New particle formation (NPF) is an important source of cloud condensation nuclei (CCN), which affects Earth's radiative balance and global climate. The mechanism and CCN contribution of NPF at the high-altitude mountains, especially in the Tibetan Plateau (TP), was unclear due to lack of measurements. In this study, intensive measurements were conducted at the Nam Co station (4730 m a.s.l.) in the central TP during both the pre-monsoon and summer monsoon seasons. The frequencies of NPF events exhibited evident seasonal differences with 15 % in the pre-monsoon season and 80 % in the monsoon season. The comprehensive analysis of the measured condensation sink (CS), gaseous precursors and meteorological conditions, supplemented by the model simulations of SO2 and volatile organic compound (VOC), points to the organic involved nucleation as the dominant mechanism. Condensation sink and gaseous sulfuric acid could have no significant effect on the occurrence of NPF events. The frequent NPF events in the summer monsoon season may result from the higher frequency of southerly and southwesterly air masses, which brought the organic precursors to participate in the NPF process. It had increased the aerosol number concentrations and CCN at supersaturation of 1.2 % by more than 2 and 0.6 times compared with those in the pre-monsoon season, respectively. Considering that the smaller particles formed by NPF may further grow and reach CCN size during the following days due to the low-level coagulation sink, the amount of potential CCN in the monsoon season could be much larger than our local measurement results. Our results emphasized the importance of considering the seasonal effect of NPF when simulating the amounts of aerosols and CCN in the high-altitude atmosphere. Long-term investigations with a full set of instrumentation are required for deeper scientific understanding of NPF process and its role in the global budget in the TP.

Abstract. Number concentrations, size distributions, and mixing states of aerosols are essential parameters for accurate estimations of aerosol direct and indirect effects. In this study, we develop an aerosol module, designated the Aerosol Two-dimensional bin module for foRmation and Aging Simulation (ATRAS), that can explicitly represent these parameters by considering new particle formation (NPF), black carbon (BC) aging, and secondary organic aerosol (SOA) processes. A two-dimensional bin representation is used for particles with dry diameters from 40 nm to 10 μm to resolve both aerosol sizes (12 bins) and BC mixing states (10 bins) for a total of 120 bins. The particles with diameters between 1 and 40 nm are resolved using additional eight size bins to calculate NPF. The ATRAS module is implemented in the WRF-Chem model and applied to examine the sensitivity of simulated mass, number, size distributions, and optical and radiative parameters of aerosols to NPF, BC aging, and SOA processes over East Asia during the spring of 2009. The BC absorption enhancement by coating materials is about 50% over East Asia during the spring, and the contribution of SOA processes to the absorption enhancement is estimated to be 10–20% over northern East Asia and 20–35% over southern East Asia. A clear north–south contrast is also found between the impacts of NPF and SOA processes on cloud condensation nuclei (CCN) concentrations: NPF increases CCN concentrations at higher supersaturations (smaller particles) over northern East Asia, whereas SOA increases CCN concentrations at lower supersaturations (larger particles) over southern East Asia. The application of ATRAS in East Asia also shows that the impact of each process on each optical and radiative parameter depends strongly on the process and the parameter in question. The module can be used in the future as a benchmark model to evaluate the accuracy of simpler aerosol models and examine interactions between NPF, BC aging, and SOA processes under different meteorological conditions and emissions.

Abstract. Atmospheric aerosols play critical roles in air quality, public health, and visibility. In addition, they strongly influence climate by scattering solar radiation and by changing the reflectivity and lifetime of clouds. One major but still poorly understood source of atmospheric aerosols is new particle formation, which consists of the formation of thermodynamically stable clusters from trace gas molecules (homogeneous nucleation) followed by growth of these clusters to a detectable size (~3 nm). Because freshly nucleated clusters are most susceptible to loss due to high rate of coagulation with pre-existing aerosol population, the initial growth rate strongly influences the rate of new particle formation and ambient aerosol population. Whereas many field observations and modeling studies indicate that organics enhance the initial growth of the clusters and therefore new particle formation, thermodynamic considerations would suggest that the strong increase of equilibrium vapor concentration due to cluster surface curvature (Kelvin effect) may prevent ambient organics from condensing on these small clusters. Here, the contribution of organics to the initial cluster growth is described as heterogeneous nucleation of organic molecules onto these clusters. We find that the strong gradient in cluster population with respect to its size leads to positive cluster number flux. This positive flux drives the growth of clusters substantially smaller than the Kelvin diameter, conventionally considered the minimum particle size that can be grown through condensation. The conventional approach neglects the contribution from the cluster concentration gradient, and underestimates the cluster survival probabilities by a factor of up to 60 if early growth of clusters is due to both condensation of sulfuric acid and heterogeneous nucleation of organic vapors.

A total of 16 global chemistry transport models and general circulation models have participated in this study; 14 models have been evaluated with regard to their ability to reproduce the near-surface observed number concentration of aerosol particles and cloud condensation nuclei (CCN), as well as derived cloud droplet number concentration (CDNC). Model results for the period 2011–2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments and on the seasonal and short-term variability in the aerosol properties.There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of −24% and −35% for particles with dry diameters > 50 and > 120nm, as well as −36% and −34% for CCN at supersaturations of 0.2% and 1.0%, respectively. However, they seem to behave differently for particles activating at very low supersaturations (< 0.1 %) than at higher ones. A total of 15 models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N3 (number concentration of particles with dry diameters larger than 3 nm) and up to about 1 for simulated CCN in the extra-polar regions. A global mean reduction of a factor of about 2 is found in the model diversity for CCN at a supersaturation of 0.2% (CCN0.2) compared to that for N3, maximizing over regions where new particle formation is important.An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter.Models capture the relative amplitude of the seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120 nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40% during winter and 20% in summer.In contrast to the large spread in simulated aerosol particle and CCN number concentrations, the CDNC derived from simulated CCN spectra is less diverse and in better agreement with CDNC estimates consistently derived from the observations (average NMB −13% and −22% for updraft velocities 0.3 and 0.6 ms−1, respectively). In addition, simulated CDNC is in slightly better agreement with observationally derived values at lower than at higher updraft velocities (index of agreement 0.64 vs. 0.65). The reduced spread of CDNC compared to that of CCN is attributed to the sublinear response of CDNC to aerosol particle number variations and the negative correlation between the sensitivities of CDNC to aerosol particle number concentration (∂Nd/∂Na) and to updraft velocity (∂Nd/∂w). Overall, we find that while CCN is controlled by both aerosol particle number and composition, CDNC is sensitive to CCN at low and moderate CCN concentrations and to the updraft velocity when CCN levels are high. Discrepancies are found in sensitivities ∂Nd/∂Na and ∂Nd/∂w; models may be predisposed to be too “aerosol sensitive” or “aerosol insensitive” in aerosol–cloud–climate interaction studies, even if they may capture average droplet numbers well. This is a subtle but profound finding that only the sensitivities can clearly reveal and may explain inter-model biases on the aerosol indirect effect.

Abstract. Atmospheric aerosol particles serving as Cloud Condensation Nuclei (CCN) are key elements of the hydrological cycle and climate. We measured and characterized CCN in polluted air and biomass burning smoke during the PRIDE-PRD2006 campaign from 1–30 July 2006 at a rural site ~60 km northwest of the mega-city Guangzhou in southeastern China. CCN efficiency spectra (activated fraction vs. dry particle diameter; 20–290 nm) were recorded at water vapor supersaturations (S) in the range of 0.068% to 1.27%. The corresponding effective hygroscopicity parameters describing the influence of particle composition on CCN activity were in the range of κ≈0.1–0.5. The campaign average value of κ=0.3 equals the average value of κ for other continental locations. During a strong local biomass burning event, the average value of κ dropped to 0.2, which can be considered as characteristic for freshly emitted smoke from the burning of agricultural waste. At low S (≤0.27%), the maximum activated fraction remained generally well below one, indicating substantial portions of externally mixed CCN-inactive particles with much lower hygroscopicity – most likely soot particles (up to ~60% at ~250 nm). The mean CCN number concentrations (NCCN,S) ranged from 1000 cm−3 at S=0.068% to 16 000 cm−3 at S=1.27%, which is about two orders of magnitude higher than in pristine air. Nevertheless, the ratios between CCN concentration and total aerosol particle concentration (integral CCN efficiencies) were similar to the ratios observed in pristine continental air (~6% to ~85% at S=0.068% to 1.27%). Based on the measurement data, we have tested different model approaches for the approximation/prediction of NCCN,S. Depending on S and on the model approach, the relative deviations between observed and predicted NCCN,S ranged from a few percent to several hundred percent. The largest deviations occurred at low S with a simple power law. With a Köhler model using variable κ values obtained from individual CCN efficiency spectra, the relative deviations were on average less than ~10% and hardly exceeded 20%, confirming the applicability of the κ-Köhler model approach for efficient description of the CCN activity of atmospheric aerosols. Note, however, that different types of κ-parameters must be distinguished for external mixtures of CCN-active and -inactive aerosol particles (κa, κt, κcut). Using a constant average hygroscopicity parameter (κ=0.3) and variable size distributions as measured, the deviations between observed and predicted CCN concentrations were on average less than 20%. In contrast, model calculations using variable hygroscopicity parameters as measured and constant size distributions led to much higher deviations: ~70% for the campaign average size distribution, ~80% for a generic rural size distribution, and ~140% for a generic urban size distribution. These findings confirm earlier studies suggesting that aerosol particle number and size are the major predictors for the variability of the CCN concentration in continental boundary layer air, followed by particle composition and hygroscopicity as relatively minor modulators. Depending on the required and applicable level of detail, the information and parameterizations presented in this study should enable efficient description of the CCN activity of atmospheric aerosols in detailed process models as well as in large-scale atmospheric and climate models.

Condensation nuclei (CN) were used as a tracer in mid‐latitude aircraft experiments in April and May 1984 designed to study transport in the stratosphere. A very large scale, mean distribution of CN was determined for April 20 in the plane perpendicular to the jet stream using smoothed CN measurements and very large scale, mean potential vorticity isopleths. This very large scale, mean distribution was constructed to exclude the structures associated with waves of short vertical wavelengths. A second analysis was done on filtered CN data by Danielsen et al. [this issue] to produce a CN cross section which included the effects of waves having vertical wavelengths of the order of 1 to 3 km. These two analyses and the waves inferred from the meteorological and tracer data produce a self‐consistent explanation for the observed spatial distribution of CN on April 20. The very large scale, mean CN distribution was distorted by waves which had the effect of transporting air with anticyclonic properties several degrees to the cyclonic side of the jet and created a strongly layered structure in the CN distribution.The unfiltered CN data revealed short wavelength oscillations in the CN distribution at the interface between the transported anticyclonic air parcel and the adjacent cyclonic air mass. These oscillations were also seen in the ozone data, and they increase the potential for mixing along that interface. If the mixing does occur, then a wave mechanism for cross jet transport has been observed.At altitudes above about 17 km, CN mixing ratios were affected by a high altitude source of new particles.

Simulating chemistry–aerosol–cloud–radiation–climate feedbacks over the continental U.S. using the online-coupled Weather Research Forecasting Model with chemistry (WRF/Chem)

Abstract. A significant fraction of atmospheric particles that serve as cloud condensation nuclei (CCN) are thought to originate from the condensational growth of new particle formation (NPF) from the gas phase. Here, 7 years of continuous aerosol and meteorological measurements (June 2008 to May 2015) at a remote background site of the eastern Mediterranean were recorded and analyzed to assess the impact of NPF (of 162 episodes identified) on CCN and cloud droplet number concentration (CDNC) formation in the region. A new metric is introduced to quantitatively determine the initiation and duration of the influence of NPF on the CCN spectrum. NPF days were found to increase CCN concentrations (from 0.10 % to 1.00 % supersaturation) between 29 % and 77 %. Enhanced CCN concentrations from NPF are mostly observed, as expected, under low preexisting particle concentrations and occur in the afternoon, relatively later in the winter and autumn than in the summer. Potential impacts of NPF on cloud formation were quantified by introducing the observed aerosol size distributions and chemical composition into an established cloud droplet parameterization. We find that the supersaturations that develop are very low (ranging between 0.03 % and 0.27 %) for typical boundary layer dynamics (σw ∼0.3 m s−1) and NPF is found to enhance CDNC by a modest 13 %. This considerable contrast between CCN and CDNC response is in part from the different supersaturation levels considered, but also because supersaturation drops from increasing CCN because of water vapor competition effects during the process of droplet formation. The low cloud supersaturation further delays the appearance of NPF impacts on CDNC to clouds formed in the late evening and nighttime – which has important implications for the extent and types of indirect effects induced by NPF events. An analysis based on CCN concentrations using prescribed supersaturation can provide very different, even misleading, conclusions and should therefore be avoided. The proposed approach here offers a simple, yet highly effective way for a more realistic impact assessment of NPF events on cloud formation.

&amp;lt;p&amp;gt;The Cloud Condensation Nuclei (CCN) budget, the aerosol particles population that could become cloud droplets, can be influenced by primary aerosol particles emitted by different sources (anthropogenic or biogenic) or by secondary particles that have undergone growth processes or chemical transformations. Aerosol particles originated by nucleation of precursor gases in the atmosphere have been identified as an important source of CCN particles. The influence of New Particle Formation (NPF) events to CCN concentrations is highly dependent on the environment where it takes place. Specifically, the study of the influence of NPF events on CCN concentration at high-altitude sites, where atmospheric conditions favor the formation of clouds, is a very interesting scientific goal.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;This study presents CCN measurements combined with aerosol size distribution at a high-altitude station in the South East of Spain: a remote high mountain site (Sierra Nevada; SNS, 2500 m a.s.l.). Due to its high altitude, the aerosol particles over SNS station are often representative of pristine free troposphere conditions, especially in winter and nighttime. During summer, SNS station is frequently influenced by transport of pollutants from Granada city to Sierra Nevada station as a result of mixing layer growth and the activation of the mountain-valley breeze phenomenon as well as by NPF events at midday (De Arruda Moreira et al., 2019; Casquero-Vera et al., 2020).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;In this study, we analyze the influence of NPF events to CCN concentrations during summer 2019 at the SNS high-altitude station. The study period (from June to August of 2019) was characterized by 67 NPF events, 16 undefined events and 13 non-events days. Following Rose et al. (2017) criteria, only those NPF events referred as type I, i.e. with clear particle growth from smallest sizes, were selected to investigate the contribution of NPF events on CCN concentrations. In this sense, we selected the 15 clearest NPF events for this analysis.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Results show clear differences in the diurnal evolution of CCN concentration between NPF event and non-event days, demonstrating the large influence of NPF to CCN concentrations, especially at high supersaturations (Rejano et al., 2021). NPF events have been estimated to increase the CCN concentrations by 175% at SS=0.5%, evidencing NPF events as one of the major CCN source at this mountain site&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;Acknowledgments&amp;lt;/strong&amp;gt;: This work was supported by the European Union's Horizon 2020 research and innovation programme through project ACTRIS 2 (grant agreement No 654109), by the Spanish Ministry of Economy and Competitiveness through projects CGL2016-81092-R, CGL2017-90884-REDT and RTI2018-101154-A-I00 and by University of Granada Plan Propio through Visiting Scholars program. The Spanish Ministry of Universities funds Fernando Rejano under the predoctoral program FPU (FPU19/05340).&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;amp;#160;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;&amp;lt;strong&amp;gt;References&amp;lt;/strong&amp;gt;&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Casquero-Vera, et al. (2020) Atmos. Chem. Phys. &amp;lt;strong&amp;gt;20, &amp;lt;/strong&amp;gt;14253&amp;amp;#8211;14271.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;De Arruda Moreira et al. (2019) Atmos. Chem. Phys. &amp;lt;strong&amp;gt;19&amp;lt;/strong&amp;gt;, 1263-1280.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Rejano et al. (2021) Sci. Tot Envi., &amp;lt;strong&amp;gt;762&amp;lt;/strong&amp;gt;, 143100.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;Rose et al. (2017) Atmos. Chem. Phys. &amp;lt;strong&amp;gt;17&amp;lt;/strong&amp;gt;, 1529-1541.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;tract HTML here.&amp;lt;/p&amp;gt;

Abstract. Aerosol nucleation occurs frequently in the atmosphere and is an important source of particle number. Observations suggest that nucleated particles are capable of growing to sufficiently large sizes that they act as cloud condensation nuclei (CCN), but some global models have reported that CCN concentrations are only modestly sensitive to large changes in nucleation rates. Here we present a novel approach for using long-term size distribution observations to evaluate a global aerosol model's ability to predict formation rates of CCN from nucleation and growth events. We derive from observations at five locations nucleation-relevant metrics such as nucleation rate of particles at diameter of 3 nm (J3), diameter growth rate (GR), particle survival probability (SP), condensation and coagulation sinks, and CCN formation rate (J100). These quantities are also derived for a global microphysical model, GEOS-Chem-TOMAS, and compared to the observations on a daily basis. Using GEOS-Chem-TOMAS, we simulate nucleation events predicted by ternary (with a 10−5 tuning factor) or activation nucleation over one year and find that the model slightly understates the observed annual-average CCN formation mostly due to bias in the nucleation rate predictions, but by no more than 50% in the ternary simulations. At the two locations expected to be most impacted by large-scale regional nucleation, Hyytiälä and San Pietro Capofiume, predicted annual-average CCN formation rates are within 34 and 2% of the observations, respectively. Model-predicted annual-average growth rates are within 25% across all sites but also show a slight tendency to underestimate the observations, at least in the ternary nucleation simulations. On days that the growing nucleation mode reaches 100 nm, median single-day survival probabilities to 100 nm for the model and measurements range from less than 1–6% across the five locations we considered; however, this does not include particles that may eventually grow to 100 nm after the first day. This detailed exploration of new particle formation and growth dynamics adds support to the use of global models as tools for assessing the contribution of microphysical processes such as nucleation to the total number and CCN budget.

Air quality has greatly improved in China owing to the strict control policy enforced during the last decade. This study investigated the impact of particulate pollution control on aerosol hygroscopicity and cloud condensation nuclei (CCN) activity in North China based on several data sources. The mass concentration of particles with an aerodynamic diameter smaller than 2.5 µm (PM2.5) decreased by one third from the summer of 2014 to the summer of 2020 in Xinzhou (XZ). The mass fractions of aerosol chemical components in PM2.5 also clearly changed, showing an increase in hydrophilic inorganics and a decrease in hydrophobic organics and black carbon from 2014 to 2020. Measurements of the particle number size distribution in XZ indicate that the occurrence frequency of new particle formation (NPF) events decreased significantly from 2014 to 2020, leading to a reduction in the generation of daytime ultrafine particles. The weakened NPF and increasing influence of morning and evening peak emissions modified the diurnal variations of the number concentration of condensation nuclei (N CN) and CCN (N CCN). The aerosol activation ratio was always higher in the summer of 2014 than in the summer of 2020. These results demonstrate that particulate pollution control can decrease N CN and N CCN but enhance aerosol hygroscopicity and activation ability.

<strong class="journal-contentHeaderColor">Abstract.</strong> 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&ndash;40 nm (CN_10&ndash;40) and 40&ndash;100 nm (CN_40&ndash;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 CN_10&ndash;40 and CN_40&ndash;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.

Abstract. Understanding the particle number size distributions in diversified atmospheric environments is important in order to design mitigation strategies related to submicron particles and their effects on regional air quality, haze and human health. In this study, we conducted 15 different field measurement campaigns between 2007 and 2011 at 13 individual sites in China, including five urban sites, four regional sites, three coastal/background sites and one ship cruise measurement along eastern coastline of China. Size resolved particles were measured in the 15–600 nm size range. The median particle number concentrations (PNCs) were found to vary in the range of 1.1−2.2 × 104 cm−3 at urban sites, 0.8−1.5 × 104 cm−3 at regional sites, 0.4−0.6 × 104 cm−3 at coastal/background sites, and 0.5 × 104 cm−3 during cruise measurement. Peak diameters at each of these sites varied greatly from 24 to 115 nm. Particles in the 15–25 nm (nucleation mode), 25–100 nm (Aitken mode) and 100–600 nm (accumulation mode) range showed different characteristics at each sites, indicating the features of primary emissions and secondary formation in these diversified atmospheric environments. Diurnal variations show a build-up of accumulation mode particles belt at regional sites, suggesting the contribution of regional secondary aerosol pollution. Frequencies of new particle formation (NPF) events were much higher at urban and regional sites than at coastal sites and during cruise measurement. The average growth rates (GRs) of nucleation mode particles were 8.0–10.9 nm h−1 at urban sites, 7.4–13.6 nm h−1 at regional sites and 2.8–7.5 nm h−1 at coastal sites and during cruise measurement. The high gaseous precursors and strong oxidation at urban and regional sites not only favored the formation of particles, but also accelerated the growth rate of the nucleation mode particles. No significant difference in condensation sink (CS) during NPF days were observed among different site types, suggesting that the NPF events in background areas were more influenced by the pollutant transport. In addition, average contributions of NPF events to potential cloud condensation nuclei (CCN) at 0.2% super-saturation in the afternoon of all sampling days were calculated as 11% and 6% at urban sites and regional sites, respectively. On the other hand, NPF events at coastal sites and during cruise measurement had little impact on potential production of CCN. This study provides a large data set of particle size distribution in diversified atmosphere of China, improving our general understanding of emission, secondary formation, new particle formation and corresponding CCN activity of submicron aerosols in Chinese environments.

Examination of CCN impacts on hail in a simulated supercell storm with triple-moment hail bulk microphysics