Hygroscopic Growth Factor Research Articles

Spatiotemporal changes in aerosol properties by hygroscopic growth and impacts on radiative forcing and heating rates during DISCOVER-AQ 2011

Abstract. This work focuses on the characterization of vertically resolved aerosol hygroscopicity properties and their direct radiative effects through a unique combination of ground-based and airborne remote sensing measurements during the Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) 2011 field campaign in the Baltimore–Washington DC metropolitan area. To that end, we combined aerosol measurements from a multiwavelength Raman lidar located at NASA Goddard Space Flight Center and the airborne NASA Langley High Spectral Resolution Lidar-1 (HSRL-1) lidar system. In situ measurements aboard the P-3B airplane and ground-based Aerosol Robotic Network – Distributed Regional Aerosol Gridded Observational Network (AERONET-DRAGON) served to validate and complement quantifications of aerosol hygroscopicity from lidar measurements and also to extend the study both temporally and spatially. The focus here is on 22 and 29 July 2011, which were very humid days and characterized by a stable atmosphere and increasing relative humidity with height in the planetary boundary layer (PBL). Combined lidar and radiosonde (temperature and water vapor mixing ratio) measurements allowed the retrieval of the Hänel hygroscopic growth factor which agreed with that obtained from airborne in situ measurements and also explained the significant increase of extinction and backscattering with height. Airborne measurements also confirmed aerosol hygroscopicity throughout the entire day in the PBL and identified sulfates and water-soluble organic carbon as the main species of aerosol particles. The combined Raman and HSRL-1 measurements permitted the inversion for aerosol microphysical properties revealing an increase of particle radius with altitude consistent with hygroscopic growth. Aerosol hygroscopicity pattern served as a possible explanation of aerosol optical depth increases during the day, particularly for fine-mode particles. Lidar measurements were used as input to the libRadtran radiative transfer code to obtain vertically resolved aerosol radiative effects and heating rates under dry and humid conditions, and the results reveal that aerosol hygroscopicity is responsible for larger cooling effects in the shortwave range (7–10 W m−2 depending on aerosol load) near the ground, while heating rates produced a warming of 0.12 K d−1 near the top of PBL where aerosol hygroscopic growth was highest.

Phase state of secondary organic aerosol in chamber photo-oxidation of mixed precursors

Abstract. The phase behaviour of aerosol particles plays a profound role in atmospheric physicochemical processes, influencing their physical and optical properties and further impacting climate and air quality. However, understanding of the aerosol phase state is still incomplete, especially that of multicomponent particles which contain inorganic compounds and secondary organic aerosol (SOA) from mixed volatile organic compound (VOC) precursors. We report measurements conducted in the Manchester Aerosol Chamber (MAC) to investigate the aerosol rebounding tendency, measured as the bounce fraction, as a surrogate of the aerosol phase state during SOA formation from photo-oxidation of biogenic (α-pinene and isoprene) and anthropogenic (o-cresol) VOCs and their binary mixtures on deliquescent ammonium sulfate seed. Aerosol phase state is dependent on relative humidity (RH) and chemical composition (key factors determining aerosol water uptake). Liquid (bounce fraction; BF < 0.2) at RH > 80 % and nonliquid behaviour (BF > 0.8) at RH < 30 % were observed, with a liquid-to-nonliquid transition with decreasing RH between 30 % and 80 %. This RH-dependent phase behaviour (RHBF=0.2,0.5,0.8) increased towards a maximum, with an increasing organic–inorganic mass ratio (MRorg/inorg) during SOA formation evolution in all investigated VOC systems. With the use of comparable initial ammonium sulfate seed concentration, the SOA production rate of the VOC systems determines the MRorg/inorg and, consequently, the change in the phase behaviour. Although less important than RH and MRorg/inorg, the SOA composition plays a second-order role, with differences in the liquid-to-nonliquid transition at moderate MRorg/inorg of ∼1 observed between biogenic-only (anthropogenic-free) and anthropogenic-containing VOC systems. Considering the combining role of the RH and chemical composition in aerosol phase state, the BF decreased monotonically with increasing hygroscopic growth factor (GF), and the BF was ∼0 when GF was larger than 1.15. The real atmospheric consequences of our results are that any processes changing ambient RH or MRorg/inorg (aerosol liquid water) will influence their phase state. Where abundant anthropogenic VOCs contribute to SOA, compositional changes in SOA may influence phase behaviour at moderate organic mass fraction (∼50 %) compared with purely biogenic SOA. Further studies are needed on more complex and realistic atmospheric mixtures.

Hygroscopicity of Water‐Soluble PM2.5 in Rural Northwest China: Contrasting Contributors Between Summer and Winter

AbstractIn this study, we investigated the chemical composition and hygroscopicity of water‐soluble fraction in PM2.5 collected from a rural site of Guanzhong Basin, a highly polluted region in northwest China. We found that inorganic components are the main substances promoting the hygroscopic properties of particulate matter (PH) in summer, while in winter, an increasing contribution from water‐soluble organic matters (WSOM) was observed. The sulfate‐nitrate‐ammonium concentration is higher on heavily polluted days, and a high concentration of water‐soluble organic matter was observed in non‐polluting days. Hygroscopic growth factors, g(RH), with elevated relative humidity (RH) of water‐soluble matter (WSM) were measured for 50, 75, 100, 125, 150 nm by hygroscopic tandem differential mobility analyzer. An initial dry particle diameter of 100 nm was chosen as the research object because the particle size has little effect on the hygroscopic growth factor at RH = 90%. The g(90%)WSM and κWSM was in the range of 1.19–1.49 and 0.06–0.22 in summer, 1.24–1.49 and 0.08–0.22 in winter, respectively, which is similar to the hygroscopicity parameters of PH produced by biomass burning. The g(90%)WSOM and κWSOM, obtained using E‐AIM model and Zdanovskii‐Stokes‐Robinson approach, were in the range of 1.06–1.69 and 0.02–0.36 in summer, 1.06–1.58 and 0.02–0.28 in winter, respectively. The hygroscopicity parameters of water‐soluble organic matter is close to the value of levoglucosan, an indicator of biomass burning, implying this region is highly affected by biomass burning. Overall, our results revealed that PM2.5 in rural regions of Guanzhong Basin is mainly influenced by biomass burning.

Impact of aerosol liquid water content and its size distribution on hygroscopic growth factor in urban Guangzhou of South China

To investigate the dependence of hygroscopic growth factor (f(RH)) on aerosol liquid water content (ALWC) and its size distribution, a comprehensive campaign was carried out in urban Guangzhou in autumn 2015. Major chemical components in bulk as well as size-segregated PM2.5 samples, bulk PM10 mass, aerosol scattering coefficient (bsp) under dry and wet conditions, inline water-soluble inorganic ions (WSIIs) and meteorological parameters were synchronously measured. Mass fractions of hydrophilic chemical composition (e.g. SO42−, NO3− and NH4+) in PM2.5 and their mass median aerodynamic diameters (MMADs) were evidently larger under conditions of ambient relative humidity (RH) >60% than RH <60%. The estimated f(RH) by the revised IMPROVE formula and the Mie model based on filter-collected WSIIs concentrations was higher than and close to the measured ones, respectively, when RH < 60%, but was evidently lower than the measured ones when RH > 60%. A good linear correlation was found between the measured f(RH) and mass ratio of ALWC to PM2.5 when using the inline WSIIs concentrations, suggesting a strong dependence of f(RH) on the mass fraction of ALWC in PM2.5.

The impact of atmospheric oxidation on hygroscopicity and cloud droplet activation of inorganic sea spray aerosol

Sea spray aerosol (SSA) contributes significantly to natural aerosol particle concentrations globally, in marine areas even dominantly. The potential changes of the omnipresent inorganic fraction of SSA due to atmospheric ageing is largely unexplored. In the atmosphere, SSA may exist as aqueous phase solution droplets or as dried solid or amorphous particles. We demonstrate that ageing of liquid NaCl and artificial sea salt aerosol by exposure to ozone and UV light leads to a substantial decrease in hygroscopicity and cloud activation potential of the dried particles of the same size. The results point towards surface reactions on the liquid aerosols that are more crucial for small particles and the formation of salt structures with water bound within the dried aerosols, termed hydrates. Our findings suggest an increased formation of hydrate forming salts during ageing and the presence of hydrates in dried SSA. Field observations indicate a reduced hygroscopic growth factor of sub-micrometre SSA in the marine atmosphere compared to fresh laboratory generated NaCl or sea salt of the same dry size, which is typically attributed to organic matter or sulphates. Aged inorganic sea salt offers an additional explanation for such a measured reduced hygroscopic growth factor and cloud activation potential.

In situ measurements of human cough aerosol hygroscopicity.

The airborne dynamics of respiratory droplets, and the transmission routes of pathogens embedded within them, are governed primarily by the diameter of the particles. These particles are composed of the fluid which lines the respiratory tract, and is primarily mucins and salts, which will interact with the atmosphere and evaporate to reach an equilibrium diameter. Measuring organic volume fraction (OVF) of cough aerosol has proved challenging due to large variability and low material volume produced after coughing. Here, the diametric hygroscopic growth factors (GF) of the cough aerosol produced by healthy participants were measured in situ using a rotating aerosol suspension chamber and a humidification tandem differential mobility analyser. Using hygroscopicity models, it was estimated that the average OVF in the evaporated cough aerosol was 0.88 ± 0.07 and the average GF at 90% relative humidity (RH) was 1.31 ± 0.03. To reach equilibrium in dry air the droplets will reduce in diameter by a factor of approximately 2.8 with an evaporation factor of 0.36 ± 0.05. Hysteresis was observed in cough aerosol at RH = ∼35% and RH = ∼65% for efflorescence and deliquescence, respectively, and may depend on the OVF. The same behaviour and GF were observed in nebulized bovine bronchoalveolar lavage fluid.

Humidity-Dependent Survival of an Airborne Influenza A Virus: Practical Implications for Controlling Airborne Viruses

Relative humidity (RH) can affect influenza A virus (IAV) survival. However, the mechanism driving this relationship is unknown. We hypothesized that the RH-dependent survival of airborne IAV could be predicted by the efflorescence/deliquescence divergent infectivity (EDDI) hypothesis. We determined three distinct RH response zones based on the hygroscopic growth factor of carrier aerosols. These zones were classified as the super-deliquescence zone (RH > 75%), the hysteresis zone (43% < RH < 75%), and the sub-efflorescence zone (RH < 43%). We added IAV (H3N2) to protein-enriched saline and aerosolized it into sub-efflorescence or superdeliquescence zone air, yielding aerosols in the effloresced or noneffloresced state, respectively. We then adjusted the RH to an ergonomically comfortable RH (60%). Fifteen minutes post-aerosolization, the surviving fractions (arithmetic means ± standard errors) of virus were higher in effloresced aerosols (9.5 ± 0.5%) than in non-effloresced aerosols (0.40 ± 0.05%). A virus suspension was also aerosolized directly into air within the super-deliquescence, hysteresis, and sub-efflorescence zones to assess the impact of the sudden change in RH from an initial 100% saturated RH to these zonal ranges. Fifteen minutes post-aerosolization, the surviving fractions were 3 ± 0.4%, 2 ± 0.1%, and 12 ± 2%, respectively. Survival following gradual adaptation to the hysteresis zone RH range was sustained in effloresced and reduced in the non-effloresced aerosols. The EDDI model predicted the survival of IAV under seasonal conditions, offering strategies for controlling indoor air infection.

Estimation of hygroscopic growth properties of source-related sub-micrometre particle types in a mixed urban aerosol

Knowledge of hygroscopic properties is essential to prediction of the role of aerosol in cloud formation and lung deposition. Our objective was to introduce a new approach to classify and predict the hygroscopic growth factors (Gfs) of specific atmospheric sub-micrometre particle types in a mixed aerosol based on measurements of the ensemble hygroscopic growth factors and particle number size distribution (PNSD). Based on a non-linear regression model between aerosol source contributions from PMF applied to the PNSD data set and the measured Gf values (at 90% relative humidity) of ambient aerosols, the estimated mean Gf values for secondary inorganic, mixed secondary, nucleation, urban background, fresh, and aged traffic-generated particle classes at a diameter of 110 nm were found to be 1.51, 1.34, 1.12, 1.33, 1.09 and 1.10, respectively. It is found possible to impute (fill) missing HTDMA data sets using a Random Forest regression on PNSD and meteorological conditions.

Hygroscopic growth of aerosol particles consisted of oxalic acid and its internal mixture with ammonium sulfate for the relative humidity ranging from 80% to 99.5%

The hygroscopicity of atmospheric aerosol particles plays an important role in their effects on the environment and the public health. Oxalic acid (OA) has been recognized as the dominant dicarboxylic acid in the urban and the remote aerosol particles, so a number of studies have investigated the hygroscopicity of aerosols consisted of pure OA and its mixture with inorganic salt. However, few experimental studies have focused on the hygroscopicity of nanoscale particles at high relative humidity (RH) below saturation of water vapor (i.e., RH = 90–100%) due to the limitation of traditional measuring instruments. In this work, the hygroscopic growth factor (GF) of the aerosol particles composed of pure OA and internally mixed OA-ammonium sulfate (AS) at RH = 80–99.5% were studied using a high humidity tandem differential mobility analyzer (HHTDMA). The experimental results were used to verify the applicability of models including the ideal solution model, the extended aerosol inorganics model (E-AIM) combining with the revised universal quasi-chemical functional group activity coefficients (UNIFAC-Peng) model, the Aerosol Inorganic–Organic Mixtures Functional groups Activity Coefficients (AIOMFAC) model and the Zdanovskii–Stokes–Robinson (ZSR) model. According to the experimental results, the effect of RH, the composition and the initial dry particle diameter (D0) on the hygroscopic growth factor (GF) and the effective hygroscopicity parameter (κ) of particles at RH = 80–99.5% were analyzed in details. It has been found that for pure OA particles with D0 = 80/100 nm, the prediction of the UNIFAC-Peng model and the AIOMFAC model becomes more accurate than the ideal solution model with the increasing of RH, while all models cannot describe the GF of smaller particles at RH = 80–99.5%. For mixed OA-AS aerosol particles, the chemical reaction is an important reason for the discrepancies between the HHTDMA results and the model prediction. For the pure OA aerosol particles at RH ≤ 96% and particles containing AS at RH ≤ 99.5%, the sensitivity of GF to D0 is positively and negatively correlated with RH and D0, respectively. However, for all aerosol types in this study, the sensitivity of GF to RH is positively correlated with both D0 and RH. In addition, the κ based on the measurement is clearly dependent on D0 (at RH = 95–99.5%), RH and the particle composition (at RH = 80–99.5%). The measured hygroscopicity of aerosol particles at high RH might be useful in addressing challenges in solving the discrepancies between the κ measured under subsaturated and supersaturated conditions.

Effect of mixing structure on the water uptake of mixtures of ammonium sulfate and phthalic acid particles

Abstract. Aerosol mixing state regulates the interactions between water molecules and particles and thus controls aerosol activation and hygroscopic growth, which thereby influences visibility degradation, cloud formation, and its radiative forcing. There are, however, few current studies on the mixing structure effects on aerosol hygroscopicity. Here, we investigated the hygroscopicity of ammonium sulfate / phthalic acid (AS / PA) aerosol particles with different mass fractions of PA in different mixing states in terms of initial particle generation. Firstly, the effect of PA coatings on the hygroscopic behavior of the core-shell-generated mixtures of AS with PA was studied using a coating hygroscopicity tandem differential mobility analyzer (coating HTDMA). The slow increase in the hygroscopic growth factor of core-shell-generated particles is observed with increasing thickness of the coating PA prior to the deliquescence relative humidity (DRH) of AS. At relative humidity (RH) above 80 %, a decrease in the hygroscopic growth factor of particles occurs as the thickness of the PA shell increases, which indicates that the increase of PA mass fractions leads to a reduction of the overall core-shell-generated particle hygroscopicity. In addition, the use of the Zdanovskii–Stokes–Robinson (ZSR) relation leads to the underestimation of the measured growth factors of core-shell-generated particles without consideration of the morphological effect of core-shell-generated particles, especially at higher RH. Secondly, in the case of the AS / PA initially well-mixed particles, a shift of the DRH of AS (∼80 %, Tang and Munkelwitz, 1994) to lower RH is observed due to the presence of PA in the initially well-mixed particles. The predicted hygroscopic growth factor using the ZSR relation is consistent with the measured hygroscopic growth factor of the initially well-mixed particles. Moreover, we compared and discussed the influence of mixing states on the water uptake of AS / PA aerosol particles. It is found that the hygroscopic growth factor of the core-shell-generated particles is slightly higher than that of the initially well-mixed particles with the same mass fractions of PA at RH above 80 %. The observation of AS / PA particles may contribute to a growing field of knowledge regarding the influence of coating properties and mixing structure on water uptake.

Size Distribution of Aerosol Hygroscopic Growth Factors in Winter in Tianjin

Aerosol hygroscopic growth factors[g(RH)] are key for evaluating aerosol light extinction and direct radiative forcing. The hygroscopic tandem differential mobility analyzer (HTDMA) was utilized to measure the size-resolved gm(RH) under different polluted conditions in winter in Tianjin. Furthermore, based on the size distribution of aerosol water-soluble ions, the gκ(RH) across a wide size range (60 nm to 9.8 μm) was estimated using the κ-Köhler theory, which provides a basis for the estimation of aerosol optical parameters and direct radiative forcing under ambient conditions. Under clean conditions, ultrafine particles (<100 nm) were more hygroscopic and gm(RH=80%) was higher than 1.30 due to the active photolysis reaction. However, under severely polluted conditions, the proportion of water-soluble ions in aerosols increased with the increasing size; gm(RH) increased with particle size, where gm(RH=80%) and gm(RH=85%) for 300 nm particles was 1.39 and 1.46, respectively. For a wide size range (60 nm to 9.8 μm), the aerosols in the accumulation mode were more hygroscopic and aerosols in the Aitken mode were less hygroscopic, with coarse mode aerosols being the least hygroscopic. During the polluted period, the particulate size notably increased, and the mass fraction of NO3- and SO42- in the accumulation mode aerosols was significantly higher than during the clean period. Accordingly, the hygroscopicity of accumulation mode aerosols was strongly enhanced during the polluted period[gκ(RH)=1.3-1.4] and aerosols in the 0.18-3.1 μm size range all had a strong hygroscopicity. On polluted days, the synergistic effect of the increase in particle size, water-soluble ions, and aerosol hygroscopicity results in the considerable deterioration of visibility.

A novel lidar system for profiling the aerosol hygroscopic growth factor

The scattering growth factor is an important parameter for description of aerosol hygroscopic growth properties. In this work, a multi-wavelength polarized Raman lidar system is designed that detects the hygroscopic characteristics of aerosol particles. The principle of the aerosol hygroscopic growth factor retrieval method is described in detail. To verify the feasibility of this lidar system, numerical simulations are performed. In the simulations, a 532 nm laser with energy of 440 mJ and a 10 Hz pulse repetition rate is used as the source, a 400-mm-diameter Cassegrain reflecting telescope collects the backscattered return signals, and the 1976 US standard model with a Mie scattering profile from practical observations is used to simulate the atmospheric environment. The results show that the lidar system is able to detect the aerosol hygroscopic growth factor profiles.

The effects of physical and chemical characteristics of aerosol number concentration on scattering coefficients in Nanjing, China: Insights from a single particle aerosol mass spectrometer

The physical and chemical characteristics of aerosols have a significant effect on scattering coefficients (σsp). In this research, a single particle aerosol mass spectrometer (SPAMS) and a scanning mobility particle sizer spectrometer (SMPS) were used to measure the chemical composition and size distribution of aerosol number concentration in Nanjing, China. During the observation time, the average σsp varied from 11.64 to 485.84 Mm−1, with an average of 114.16 ± 77.87 Mm−1. For relative humidity greater than 75.0%, the optical hygroscopic growth factor (f(RH)) increased rapidly, with an approximate distribution of 3.41 ± 0.78. During the night of July 15th, 2015, nitrate and sulfate increased by 5.93 and 1.32 times, respectively, compared with daytime values. The peak of the average size distribution of the aerosol number concentration during the observation period (341.0 cm−3) was located in the Aitken mode of 58.3 nm. After particle size conversion from the vacuum aerodynamic diameter to the mobility diameter, the particle size range of the aerosol mass spectrometer ranged from 138.2–723.4 nm, all of which are distributed in accumulation mode. Source apportionment revealed that secondary, biomass, and carbonaceous aerosols are the primary facilitators in 327.8–406.8 nm, accounting for 21.3%, 25.7%, and 33.3%, respectively. The fixed scattering coefficients were calculated using the Mie model, according to the source apportionment of aerosol number concentration for modifying the aerosol refractive index. From July 6th–11th, the calculation and observation results of σsp exhibit excellent consistency and a Pearson coefficient of 0.66. Therefore, the accurate size distribution of the chemical composition and source apportionment of aerosols are of great significance for the simulation of atmospheric optical scattering.

Exploring the relationship between high-resolution aerosol optical depth values and ground-level particulate matter concentrations in the Metropolitan Area of São Paulo

The spatiotemporal pattern of particulate matter (PM) concentrations is an important factor in predicting health issues in inhabitants of urban areas. The integration of satellite-derived aerosol optical depth (AOD) data with ground-level PM concentration data, obtained from monitoring networks, has contributed to better characterization of the spatiotemporal variability of aerosols worldwide. However, before using satellite AOD data as a proxy for PM in epidemiological and air quality studies in specific regions, the applicability of that strategy must be evaluated. In this study, we evaluate the use of the high-resolution AOD, derived from Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm, as a predictor of surface PM concentrations in the Metropolitan Area of São Paulo (MASP). We found relatively weak or negative correlations between PM concentrations and MAIAC AOD, even after vertical correction by planetary boundary layer height and the hygroscopic growth factor. The weak correlations reported in this study are mainly due to the mismatch between the current MAIAC aerosol model and the properties of local aerosols in the MASP. Our results suggest that sources of aerosol particles in the MASP are quite diverse and that there is therefore no single optical model suitable for use with satellite-derived AOD.

Approximated expression of the hygroscopic growth factor for polydispersed aerosols

Hygroscopic growth of aerosols plays an important role in the characterization of atmospheric aerosols. Physico-chemical and optical properties of aerosols are dependent on relative humidity (RH) as well as on their size and composition. In this study, scattering enhancement factors, f(RH), for polydispersed aerosols were approximated. f(RH) of ammonium sulfate and ammonium nitrate (AS) and NaCl aerosols (ss) were considered under the assumption of externally mixed aerosols. f(RH) was calculated using the Mie theory for polydispersed aerosols at a given RH and corresponding water uptake (denoted as fMie(RH)). f(RH) was approximated as a quadratic function of RH (denoted as fapp(RH)). The obtained approximated f(RH) or fapp(RH)) values were compared with the values based on the Mie theory and showed a reasonable agreement between them. To the best of our knowledge, this is the first study that parametrizes the size dependency of f(RH) for log normally distributed aerosols.

Comparison of physical and chemical characteristics and oxidative potential of fine particles emitted from rice straw and pine stem burning

Agricultural burning and forest fires are common in Northeast Asia and contribute to the elevation of fine particulate pollution, which greatly affects air quality. In this study, chemical and physical attributes, as well as the oxidative potential of fine particles produced from rice straw and pine stem burning in a laboratory-scale chamber were determined. The burning of rice straw generated notably lower emissions of fine particles and elemental carbon (EC) than did the burning of pine stems. The longer retention of ultrafine particles was observed for rice straw burning likely caused by this material’s longer period of initial flaming combustion. Organic carbon (OC), OC/EC, K+/OC, K+/EC, Zn, and alkanoic acid were higher in the fine particles of rice straw burning, while EC, K+/Cl−, Fe, Cr, Al, Cu, and levoglucosan were higher for pine stem burning particles. Chemical data were consistent with a higher hygroscopic growth factor and cloud formation potential and lower amount of agglomerated soot for rice straw burning particles. Rice straw burning particles displayed an oxidative potential seven times higher than that of pine stems.

Analysis of hygroscopic growth properties of soluble aerosol under severe nuclear accidents conditions

Radioactive aerosol released under severe nuclear accidents conditions contains large amounts of soluble compounds. The hygroscopic growth of soluble aerosol enable to enlarge the particle size and affect the subsequent deposition behavior, which plays an important role on source term analysis. However, the investigation about hygroscopic growth properties of typical nuclear aerosol viz. Cesium iodine and cesium hydroxide, has been largely lacking and the hygroscopic model in MELCOR also need to validate and evaluate. In this paper, steady-state hygroscopic model based on Köhler theory was used to predict the hygroscopic growth factors of these two kinds of aerosols. Sensitivity analysis of surface tension and water activity of aqueous-solution droplet on hygroscopic growth factor were performed, and the prediction results were compared with the experimental data to evaluate MELCOR. The results show that the simplification of replacing surface tension of salt droplet with pure water in MELCOR is acceptable. The processing method of water activity in MELCOR overestimates the hygroscopic growth factors of cesium hydroxide, while its predictions are much close to the hygroscopic growth factors of cesium iodine. The improved model has higher prediction accuracy than MELCOR. In addition, the transient hygroscopic growth rate model was also used to analyze the effects of operating parameters on the hygroscopic growth characteristics of soluble aerosol. The hygroscopic growth rate is proportional to the relative humidity, particle size and gas temperature. Aerosol particles with larger initial size under higher relative humidity condition require longer time to attain equilibrium state, and the equilibrium time decreases with the increasing gas temperature. This study can provide theoretical reference for fundamental understanding of hygroscopic growth properties of soluble aerosol and the estimation of aerosol source terms under severe nuclear accidents conditions.

Sea spray aerosol organic enrichment, water uptake and surface tension effects

Abstract. The aerosol-driven radiative effects on marine low-level cloud represent a large uncertainty in climate simulations, in particular over the Southern Ocean, which is also an important region for sea spray aerosol production. Observations of sea spray aerosol organic enrichment and the resulting impact on water uptake over the remote Southern Hemisphere are scarce, and therefore the region is under-represented in existing parameterisations. The Surface Ocean Aerosol Production (SOAP) voyage was a 23 d voyage which sampled three phytoplankton blooms in the highly productive water of the Chatham Rise, east of New Zealand. In this study we examined the enrichment of organics to nascent sea spray aerosol and the modifications to sea spray aerosol water uptake using in situ chamber measurements of seawater samples taken during the SOAP voyage. Primary marine organics contributed up to 23 % of the sea spray mass for particles with diameter less than approximately 1 µm and up to 79 % of the particle volume for 50 nm diameter sea spray. The composition of the submicron organic fraction was consistent throughout the voyage and was largely composed of a polysaccharide-like component, characterised by very low alkane-to-hydroxyl-concentration ratios of approximately 0.1–0.2. The enrichment of organics was compared to the output from the chlorophyll-a-based sea spray aerosol parameterisation suggested by Gantt et al. (2011) and the OCEANFILMS (Organic Compounds from Ecosystems to Aerosols: Natural Films and Interfaces via Langmuir Molecular Surfactants) models. OCEANFILMS improved on the representation of the organic fraction predicted using chlorophyll a, in particular when the co-adsorption of polysaccharides was included; however, the model still under-predicted the proportion of polysaccharides by an average of 33 %. Nascent 50 nm diameter sea spray aerosol hygroscopic growth factors measured at 90 % relative humidity averaged 1.93±0.08 and did not decrease with increasing sea spray aerosol organic fractions. The observed hygroscopicity was greater than expected from the assumption of full solubility, particularly during the most productive phytoplankton bloom (B1), during which organic fractions were greater than approximately 0.4. The water uptake behaviour observed in this study is consistent with that observed for other measurements of phytoplankton blooms and can be partially attributed to the presence of sea salt hydrates, which lowers the sea spray aerosol hygroscopicity when the organic enrichment is low. The inclusion of surface tension effects only marginally improved the modelled hygroscopicity, and a significant discrepancy between the observed and modelled hygroscopicity at high organic volume fractions remained. The findings from the SOAP voyage highlight the influence of biologically sourced organics on sea spray aerosol composition; these data improve the capacity to parameterise sea spray aerosol organic enrichment and water uptake.

COMPARISON BETWEEN KELVIN RADII AND BULK HYGROSCOPICITY OF MASS AND VOLUME BASED HYGROSCOPICITY PARAMETER FOR ATMOSPHERIC AEROSOLS

A mass based and volume based hygroscopicities models were applied to the data extracted from Optical Properties of Aerosols and Clouds (OPAC).The microphysical properties obtained were radii, density, refractive index, mass and volume of the atmospheric aerosols of continental average, continental clean, continental polluted, maritime tropical, maritime polluted, maritime clean, at eight different relative humidity of 0%, 50%, 70%, 80%, 90%, 95%, 98% and 99%.Using the microphysical properties, hygroscopic growth factors and effective radii of the mixtures were determined while the parameters Av and Bv for volume based and Am and Bm for mass based of the aerosols were determined using multiple regression analysis with SPSS 16.0 at each relative humidity. Although it was discovered that Bv is more dominant than Av, the R2 for all the models are greater than 90%. The significances are less than 0.05, Am&gt;Av and Bm&lt;Bv, therefore the two models are good for atmospheric modeling.

Simultaneous measurements of the relative-humidity-dependent aerosol light extinction, scattering, absorption, and single-scattering albedo with a humidified cavity-enhanced albedometer

Abstract. Hygroscopic aerosols take up water and grow with increasing relative humidity (RH), giving rise to large changes in light extinction (bext), scattering (bscat), absorption (babs), and single scattering albedo (SSA, ω). The optical hygroscopic growth factors for each parameter (f(RH)ext,scat,abs,ω) are thus important for assessing aerosol effects on regional air quality, atmospheric visibility, and radiative forcing. The RH dependence of aerosol scattering and extinction has been studied in many laboratory and field studies. However, owing partly to the absence of suitable instrumentation, there are few reports of the RH dependence of aerosol absorption and ω. In this work, we report the development of a humidified cavity-enhanced albedometer (H-CEA) for simultaneous measurements of f(RH)ext,scat,abs,ω at λ=532 nm from 10 % to 88 % RH. The instrument's performance was evaluated with laboratory-generated ammonium sulfate, sodium chloride, and nigrosin aerosols. Measured hygroscopic growth factors for different parameters were in good agreement with model calculations and literature-reported values, demonstrating the accuracy of the H-CEA for measuring RH-dependent optical properties.