Condensation Nuclei Number Concentration Research Articles

The impact of particulate pollution control on aerosol hygroscopicity and CCN activity in North China

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.

Properties of particulate pollution in the port city of Valparaiso, Chile

The city of Valparaiso is home to one of the largest commercial ports on the west coast of South America. Port activities, that continue year-round, 24 h a day and seven days a week, produce emissions of pollutants, particularly aerosol particles composed of black and brown carbon (BC and BrC) that have serious impact on human population and the local environment. A measurement program was launched to document the magnitude of selected pollutants, to identify their sources and to evaluate the meteorological processes that enhance and transport these pollutants locally and regionally. In this study, we report the measurements made during four months: 25July - 25August 2014 (referred to as August 2014 throughout the manuscript), December 2014, January 2015 and March 2015. The daily mass concentrations of equivalent black carbon (eBC), derived from measurements of the light absorption coefficient, regularly exceed 5 μg m−3, a magnitude similar to values found in megacities such as Mexico City. The daily maximum number concentration of condensation nuclei (CN) is usually larger than 30000 cm−3. The Angstrom absorption exponent (AAE), derived from the absorption coefficients at 550 nm and 870 nm, is used to identify the primary sources of BC and BrC. In colder weather, emissions from the diesel fueled buses and trucks and the consumption of kerosene and wood for residential heating are the main sources of BC. In December, local wildfires contributed to the particle mass loading, but the day-to-day variability in boundary layer height and the presence of clouds and fog in occasions inhibited high concentrations. In March, the port activities reach a yearly peak during the seasonal export of agricultural products that translates into much more ship and truck traffic leading to very high eBC concentrations, comparable to values observed during August. The variability in weather patterns underscores the complexity of meteorological processes that drive the evolution and transport of pollution in Valparaiso.

A study on aerosol-cloud condensation nuclei (CCN) activation over eastern Himalaya in India

Simultaneous measurements of condensation nuclei (CN) and cloud condensation nuclei (CCN) has been performed over a high altitude site Darjeeling (27°01′N, 88°15′E, 2200m asl) at eastern part of Himalaya in India. The study was carried out during dry seasons (October 2015–May 2016) to investigate the temporal variability of CN and CCN concentrations and the major factors controlling CN-CCN activation. CCN concentrations measured at 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8 and 0.9% super saturations have been reported in this study. The number concentrations of CN ranged between 694 and 23,643cm−3 with an average of 6563±2160cm−3 whereas that of CCN (at 0.5% super saturation) ranged between 262 and 13,382cm−3 with an average of 1761±856cm−3 during the entire study period. CN and CCN showed prominent monthly and seasonal variations controlled by local emissions, meteorological factors and long-range transport. Indo-Gangetic Plain (IGP) was found to be the most contributing region for CN and CCN over Darjeeling mainly during winter and premonsoon. A clear indication of the contribution of aerosols from plain land regions driven by up-slope valley wind was observed during premonsoon from diurnal variability of CN and CCN. Overall, 30–32% aerosols were observed to activate to CCN during winter and premonsoon whereas 24% activation was observed during postmonsoon. Chemical nature and hence solubility of aerosols controlled CCN activation more in night-time than day-time as observed from the correlations between activation ratios and hygroscopicity parameter, k. Strong seasonal dependence of CCN and activation ratio on super saturation and aerosol loading was observed. We observed higher CN and CCN loading and lower activation ratio over Darjeeling compared to western Himalayan high altitude station suggesting higher influence of local and long-range aerosols over eastern Himalaya and significant difference in chemical nature of aerosols between these two parts of Himalaya.

Relationships between layer-mean radar reflectivity and columnar effective radius of warm cloud: Numerical study using a cloud microphysical bin model

The relationship between the layer-mean radar reflectivity, Ze, and the columnar effective particle radius, Re, in evolving shallow warm clouds was investigated by numerical experiments using a hybrid cloud microphysical model and a forward simulator of satellite measurements. Changes in the cloud/rain droplet size distributions were traced in a kinematically driven warm cloud for various values of number concentration of cloud condensation nuclei (CCN) and maximum updraft velocity. In contrast to previous interpretations of the observed data, we found four paths for the relationships between Ze and Re during the lifetime of a warm cloud. In the first path, both Ze and Re increase with an approximate sixth-power dependency, indicating a stage of condensational growth of droplets without raindrops in the cloud. In the second path, only Ze increases rapidly, while Re remains almost constant (Resecond), indicating a stage in which few raindrops emerge in the cloud before appreciable precipitation occurs at the surface. This second path was newly identified in this study. In the third path, Re increases rapidly while Ze does not change greatly, indicating a stage of coalescence of droplets. Precipitation reaches the surface at the end of the third path. In the fourth path, both Ze and Re decrease, indicating a greater contribution of raindrop evaporation and weakening or termination of precipitation. The maximum values of Ze and Re and the constant value of Resecond for the second stage depend on the CCN number concentration and the updraft velocity.

The environmental impact of the Puyehue–Cordon Caulle 2011 volcanic eruption on Buenos Aires

Abstract. On 4 June 2011, the volcanic complex Puyehue–Cordon Caulle located in the Chilean Andes erupted, producing a plume of gases and particles that eventually circled the Southern Hemisphere, disrupting air travel and depositing ash in large quantities. On eight occasions, the plume passed over the city of Buenos Aires, Argentina, leading local authorities to close the two international airports. The eruption occurred during an on-going field campaign when measurements of the properties of atmospheric aerosol particles were being made in Buenos Aires as part of a year-long study of the concentration and optical properties of aerosol at one site in the city. The suite of instruments deployed in Buenos Aires were not tailored to measurements of volcanic ash, but were designed to characterize urban conditions. Nevertheless, these measurements were analysed for periods when vertical profiles of aerosol backscatter, made with a ceilometer, clearly showed the presence of the volcano plume over the research site and resulted in airport closure. Aerosol optical thickness derived from AERONET, MODIS and a ceilometer at our research site, all show enhanced values clearly indicating that the three platforms identified the volcanic plume simultaneously. However, a quantitative comparison of the different estimates proves difficult, suggesting large spatial and temporal variability of the plume. Our results indicate that the number concentration of condensation nuclei (CN), the mass concentration of particle-bound polycyclic aromatic hydrocarbons (PPAH) and the light absorption coefficient exceeded the average background values by more than one standard deviation during the events of volcanic plume. The anomalous concentrations of CN suggest new particle formation, presumably from the conversion of SO2, while the anomalous concentrations of PPAH may come from the uptake of PAHs on the plume particles or from chemical reactions on the surface of plume particles. The anomalous absorption coefficients indicate that plume particles may contain certain compounds that can absorb radiation at 550 nm. Another possible explanation consistent with the observations is the scavenging of black carbon from urban sources as the plume descends through the boundary layer to the surface. In addition, the volcanic plume influenced the local meteorology resulting in a decrease of the temperature when compared to the average temperature during days with no plume present.

Temperature-dependent accumulation mode particle and cloud nuclei concentrations from biogenic sources during WACS 2010

Abstract. Submicron aerosol particles collected simultaneously at the mountain peak (2182 m a.s.l.) and at a forested mid-mountain site (1300 m a.s.l.) on Whistler Mountain, British Columbia, Canada, during June and July 2010 were analyzed by Fourier transform infrared (FTIR) spectroscopy for quantification of organic functional groups. Positive matrix factorization (PMF) was applied to the FTIR spectra. Three PMF factors associated with (1) combustion, (2) biogenics, and (3) vegetative detritus were identified at both sites. The biogenic factor was correlated with both temperature and several volatile organic compounds (VOCs). The combustion factor dominated the submicron particle mass during the beginning of the campaign, when the temperature was lower and advection was from the Vancouver area, but as the temperature started to rise in early July, the biogenic factor came to dominate as a result of increased emissions of biogenic VOCs, and thereby increased formation of secondary organic aerosol (SOA). On average, the biogenic factor represented 69% and 49% of the submicron organic particle mass at Whistler Peak and at the mid-mountain site, respectively. The lower fraction at the mid-mountain site was a result of more vegetative detritus there, and also higher influence from local combustion sources. The biogenic factor was strongly correlated (r~0.9) to number concentration of particles with diameter (Dp)> 100 nm, whereas the combustion factor was better correlated to number concentration of particles with Dp<100 nm (r~0.4). The number concentration of cloud condensation nuclei (CCN) was correlated (r~0.7) to the biogenic factor for supersaturations (S) of 0.2% or higher, which indicates that particle condensational growth from biogenic vapors was an important factor in controlling the CCN concentration for clouds where S≥0.2%. Both the number concentration of particles with Dp>100 nm and numbers of CCN for S≥0.2% were correlated to temperature. Considering the biogenic influence, these results indicate that temperature was a primary factor controlling these CCN concentrations at 0.2% supersaturation.

Decreasing particle number concentrations in a warming atmosphere and implications

Abstract. New particle formation contributes significantly to the number concentration of condensation nuclei (CN) as well as cloud CN (CCN), a key factor determining aerosol indirect radiative forcing of the climate system. Using a physics-based nucleation mechanism that is consistent with a range of field observations of aerosol formation, it is shown that projected increases in global temperatures could significantly inhibit new particle, and CCN, formation rates worldwide. An analysis of CN concentrations observed at four NOAA ESRL/GMD baseline stations since the 1970s and two other sites since 1990s reveals long-term decreasing trends that are consistent in sign with, but are larger in magnitude than, the predicted temperature effects. The possible reasons for larger observed long-term CN reductions at remote sites are discussed. The combined effects of rising temperatures on aerosol nucleation rates and other chemical and microphysical processes may imply substantial decreases in future tropospheric particle abundances associated with global warming, delineating a potentially significant feedback mechanism that increases Earth's climate sensitivity to greenhouse gas emissions. Further research is needed to quantify the magnitude of such a feedback process.

Aerosols at a mountaintop observatory in Arizona

This paper discusses physics of aerosols measured at the summit of Mt. Lemmon, Arizona (2790 m), from February to May 2002, where “clean” air representative of the free troposphere sometimes occurs. We confirmed Marti's findings of a persistent daily variation in the number concentration of condensation nuclei (diameter > 10 nm), with a strong maximum occurring in the afternoon and minimum in the early morning. These particles show evidence of growth at rates of 10–23 nm per hour. The diurnal variation was present even on days when the planetary boundary layer remained below the mountain. From the rate of growth and Maxwellian diffusion theory, we deduce that precursor condensable species are present in daytime concentrations of 107–108 cm−3, and that these are produced at a rate of 105–106 cm−3 s−1. Increased convection caused by solar heating of the mountain often carries contaminated air to the summit. Yet only a small (factor of 1.5) diurnal pattern was found for accumulation mode (diameter ∼ 130 nm) particles on days where the convective boundary layer passed well above the station. We hypothesize that these long‐lived (e.g., several days) aerosols are pumped into the free troposphere and remain behind at night in a residual layer. The free tropospheric aerosol size distribution measured at Mt. Lemmon was similar in shape but higher in magnitude (by around 50%) than at Jungfraujoch in the Swiss Alps (3580 m). There is much greater diurnal variation in Aitken‐sized particles (daily factor of from 7 to 10) at Mt. Lemmon than observed at Jungfraujoch (factor of from 1.0 to 1.6), evidently arising from stronger photochemical rate of productions of precursor gases.

Modelling and simulation of aerosol formation by heterogeneous nucleation in gas–liquid contact devices

This paper describes a new simulation tool for the prediction of aerosol formation and behaviour in gas–liquid contact devices such as absorbers, scrubbers, quench coolers, and condensers as well as multistage gas cleaning processes, respectively. Aerosol formation can impact severely the separation efficiency of gas cleaning processes. Aerosol or fog formation can arise by spontaneous condensation or desublimation in supersaturated gas phases. The rigorous description of the mass and energy transfer between the gas phase, the liquid phase, and the growing aerosol droplets leads to a system of partial differential and algebraic equations. For the solution of these systems, we have developed the plant simulation tool AerCoDe. This programme bases upon the linearly-implicit Euler discretization, which in combination with extrapolation permits an adaptive step size and order control. Typical simulation results of a multistage industrial flue gas scrubbing process are presented. It is shown, that experimental data can be confirmed if the number concentration of condensation nuclei as an input parameter is roughly known.

The influence of the organic aerosol component on CCN supersaturation spectra for different aerosol types

This paper describes the effect of the presence of water-soluble organic compounds (WSOC) in aerosol particles on the aerosol critical supersaturation as defined by the Köhler theory and on cloud condensation nuclei (CCN) number concentration. Taking into account both the soluble mass increase and the surface tension depression due to WSOC, we calculated a substantial decrease of the aerosol critical supersaturation, which results in a large increase in CCN number concentration. CCN supersaturation spectra were computed for three different aerosol types: marine, rural and urban. The increase of CCN number concentration in the presence of WSOC (with respect to the case when only the inorganic aerosol compounds are considered) varies with aerosol type, with an increase up to 13% in the marine case, up to 97% in the rural case, and up to 110% in the urban case, for the supersaturation range typical of atmospheric conditions.

A new three-stage continuous flow CCN-counter

A three-stage vertical-flow thermal gradient vapour diffusion chamber for the fast, continuous measurement of the number concentration of cloud condensation nuclei (CCN) at three different water vapour supersaturations was constructed. CCN are monitored by imaging cloud droplets in the chamber with a CCD-camera. The counting of droplets and the control of all instrumental parameters are computerized. The instrument was calibrated with NaCl-aerosols, and was successfully operated in the field. Data from 2 weeks of field measurements at an island in the North Sea are presented.

Relationships between condensation nuclei number concentration, tides, and standard meteorological variables at Mace Head, Ireland

The set of hourly averaged condensation nuclei (CN) data collected at Mace Head during 1991–1994 was examined for relationships that might exist between CN number concentrations and the more commonly measured meteorological variables, including tides. CN number concentrations at Mace Head can be characterized by typically low “background” levels (less than about 700 particles cm−3) when the wind is from the west, somewhat higher “background” levels (1000–4000 particles cm−3) when the wind is from the east, with sporadic bursts of short‐lived discrete “events” of more than 10,000 cm −3 for several hours. These events occur typically during early afternoon and are normally associated with slack winds and anomalously warm, dry air. They appear to be independent of pressure, wind direction and precipitation. They can occur any time during the year, although the strongest events tend to occur during spring and autumn. Large‐amplitude low tides also occur predominantly in the early afternoon during this observing period. We present evidence that large CN concentration events occur preferentially after exceptionally low tides during daylight. A neural network was employed to train the standard meteorological variables to predict CN concentrations. Baseline forecasts of CN counts for the final 180 days of the observing period were made using lagged values of all other variables. Further forecasts were made with some variables removed from the predictor set. The best correlation between the predicted values and the verifying data over the 180 days was 0.67, which was obtained from a 1‐hour forecast using knowledge of all variables except temperature. Other variables whose removal improved the forecast (or whose presence degraded it) were pressure and wind speed. The best predictors of CN values were wind direction, relative humidity, and time of day. An elementary “nearest neighbor,” or “historical analogue” approach to predicting the same set of CN values generated lower correlations with the verifying data but generated a much more accurate probability distribution function.

Sudden changes in arctic atmospheric aerosol concentrations during summer and autumn

The International Arctic Ocean Expedition of 1991 measured number concentrations of condensation nuclei and cloud condensation nuclei from 1 August to 6 October between latitudes 70°N and 90°N. Changes in concentration of more than a factor of 2 in 1 h or less were frequent in spite of the long distances from significant sources and often appeared in groups separated by times of the order of 1 h. These observations provide a unique opportunity to study interacting meteorological mechanisms in the stable marine boundary layer. It is suggested that most of these changes were due to two factors: (1) large vertical concentration gradients caused mainly by interaction of aerosol and clouds and (2) intermittent localised mixing into the shallow surface mixed layer, caused by atmospheric wave motions or roll vortices. Quasi-periodic changes of smaller amplitude were present for about 35% of the total time with mean periods in the range 60–90 min. About 1/6 of the sudden large changes, usually involving an isolated decrease and recovery in accumulation mode particle number concentrations, is attributed to mixing caused by shear-induced Kelvin-Helmholtz breaking waves. Regular sequences of maxima and minima were about as common but involved 2/3 of all such changes because of the number of events in each sequence. Satellite images, radiosonde wind profiles and the typical mean periods suggested that roll vortices were common in the high Arctic. The associated mixing changes seemed to account adequately for the alternating maxima and minima in aerosol number concentrations. The special conditions of atmospheric stability and high frequencies of low cloud cover in the high Arctic combined with the absence of strong local sources of particles have allowed us to identify processes of mixing that often drastically modified aerosol size distributions and concentrations near the surface which are likely to have a far more general application. These factors have to be added to studies of chemical and physical processes influencing the life cycle of the aerosol and air transport, in order to understand the sources, sinks and to define the radiative forcing by the atmospheric aerosol in the Arctic and elsewhere. DOI: 10.1034/j.1600-0889.1996.t01-1-00009.x

Sudden changes in arctic atmospheric aerosol concentrations during summer and autumn

The International Arctic Ocean Expedition of 1991 measured number concentrations of condensation nuclei and cloud condensation nuclei from 1 August to 6 October between latitudes 70°N and 90°N. Changes in concentration of more than a factor of 2 in 1 h or less were frequent in spite of the long distances from significant sources and often appeared in groups separated by times of the order of 1 h. These observations provide a unique opportunity to study interacting meteorological mechanisms in the stable marine boundary layer. It is suggested that most of these changes were due to two factors: (1) large vertical concentration gradients caused mainly by interaction of aerosol and clouds and (2) intermittent localised mixing into the shallow surface mixed layer, caused by atmospheric wave motions or roll vortices. Quasi-periodic changes of smaller amplitude were present for about 35% of the total time with mean periods in the range 60–90 min. About 1/6 of the sudden large changes, usually involving an isolated decrease and recovery in accumulation mode particle number concentrations, is attributed to mixing caused by shear-induced Kelvin-Helmholtz breaking waves. Regular sequences of maxima and minima were about as common but involved 2/3 of all such changes because of the number of events in each sequence. Satellite images, radiosonde wind profiles and the typical mean periods suggested that roll vortices were common in the high Arctic. The associated mixing changes seemed to account adequately for the alternating maxima and minima in aerosol number concentrations. The special conditions of atmospheric stability and high frequencies of low cloud cover in the high Arctic combined with the absence of strong local sources of particles have allowed us to identify processes of mixing that often drastically modified aerosol size distributions and concentrations near the surface which are likely to have a far more general application. These factors have to be added to studies of chemical and physical processes influencing the life cycle of the aerosol and air transport, in order to understand the sources, sinks and to define the radiative forcing by the atmospheric aerosol in the Arctic and elsewhere. DOI: 10.1034/j.1600-0889.1996.t01-1-00009.x

Dimethylsulfide, aerosols, and condensation nuclei over the tropical northeastern Atlantic Ocean

Concentration of dimethylsuifide (DMS) in seawater, concentrations of DMS and sulfur dioxide (SO2) in the atmosphere, concentrations of methanesulfonate (MSA) and non‐sea‐salt sulfate (nss‐SO42−) in size‐segregated aerosols, and number concentration of condensation nuclei (CN) were measured during September and October 1991 in the northern tropical Atlantic Ocean in order to assess the role of DMS in CN production over this oceanic area. Radon‐222 activity and aerosol ionic composition were used to distinguish air masses with oceanic, continental, and/or polluted characters. No obvious covariation appeared between DMS and its oxidation products (SO2, H2SO4, and MSA) over the whole period of the experiment. However, the division of data into subsets according to continental tracer information allowed us to show that SO2 and nss‐SO4 concentrations correlated with DMS concentration in unpolluted air masses. MSA and nss‐SO42− were found to be mainly concentrated in particles with diameters < of 0.6 μm. Daily mean nss‐SO42− in the <0.6‐μm‐diameter range and CN concentration were correlated (R = 0.91, n = 17, P < 0.001), which suggests that H2SO4 is an important CN precursor. Atmospheric DMS and CN number daily mean concentrations also correlated (R = 0.82, n = 21, P < 0.001). However, the CN population was strongly influenced by continental inputs less than 500 km downwind of Africa, whereas DMS seemed to be able to affect the CN number concentration at about 1500 km from this continent.

Change in concentrations of cloud condensation nuclei and aerosol particles during the dissipation of fog.

Measurements on the number concentrations of cloud condensation nuclei (CCN) and aerosol particles were carried out at Tsukuba during the dissipation stage of fog. Number concentrations of CCN in the supersaturation range of 0.24-1.24% and submicron aerosol particles with radii between 0.05 and 0.25 μm tended to increase during the dissipation of fog. Chemical elements in individual aerosol particles collected during the dissipation of fog were examined by using an electron microscope equipped with an energy-dispersive X-ray analyzer (EDX). The results of quantitative analysis indicated that sulfur was dominant in the submicrometer particles. Estimated radius growth rates of aerosol particles during the dissipation showed increase in proportion to aerosol radius, suggesting the importance of chemical reactions in fog droplets. The elemental composition of the residues of individual fog droplets was also examined with the EDX, together with that of large particles after the dissipation of fog. It was found from the quantitative analysis that the weight ratios of S/Fe and S/K in large particles were 3.5 and 5.3 times greater than those of fog droplet residues, respectively. It is suggested that SO2 oxidation took place in fog droplets. And evaporation of fog droplets will contribute to the increase in the concentrations of large particles and CCN in the lower atmosphere near the ground.

Condensation Nucleus Discriminator Making Optical Measurements on Fog: A Tool for Environmental Research

An instrument providing a new, rapid, and accurate method of determining the number and critical radii of condensation nuclei with radii under 200 angstroms is described. Based on the principle of the cloud chamber, the instrument measures transient changes in the attenuation and scattering of a monochromatic light beam by the growing fog droplets. From data obtained the absolute number concentration and radii of condensation nuclei can be calculated. Preliminary studies of aerosol formation in beta-irradiated mixtures of air and sulfur dioxide showed that carbon monoxide and methane inhibit the formation of nuclei; relative rate constants can be deduced. Some applications of this instrument for environmental and basic research are pointed out.

Considerations in the Measurement of Pollution Effects on the Number Concentration of Cloud Condensation Nuclei

Abstract Pollution effects on cloud condensation nucleus (CCN) concentration vary widely, sometimes even decreasing the CCN. The interpretation of these pollution effects may be invalid if the nuclei are measured by expansion-type Aitken nucleus counters operated at low expansion ratios to provide a readout (with natural nuclei) equal to that of a thermal-gradient diffusion cloud chamber (TGDCC) instrument operated at 1% supersaturation. Calculations indicate that the expansion chamber operated at a ΔP of 1.4 inch Hg produces a supersaturation of 26%, allowing for vapor depletion effects during the first few hundredths of a second after expansion. The maximum supersaturation in clouds is typically 0.1–1%; therefore, 26% causes a, large positive error. Further, vapor depletion in the instrument during droplet growth limits the growth rate and size of droplets at supersaturations which are low compared to those for which the instrument is designed. Therefore, use of the standard calibration curve contribute...