Over the last few years, several condensation particle counters (CPCs) capable of measuring in the sub-3 nm size range have been developed. Here we study the performance of CPCs based on diethylene ...glycol (DEG) at different temperatures during Cosmics Leaving OUtdoor Droplets (CLOUD) measurements at CERN. The data shown here are the first set of verification measurements for sub-3 nm CPCs under upper tropospheric temperatures using atmospherically relevant aerosol particles. To put the results in perspective we calibrated the DEG-CPC at room temperature, resulting in a cut-off diameter of 1.4 nm. All diameters refer to mobility equivalent diameters in this paper. At upper tropospheric temperatures ranging from 246.15 K to 207.15 K, we found cut-off sizes relative to a particle size magnifier in the range of 2.5 to 2.8 nm. Due to low number concentration after size classification, the cut-off diameters have a high uncertainty (±0.3 nm) associated with them. Operating two laminar flow DEG-CPCs with different cut-off sizes together with other aerosol instruments, we looked at the growth rates of aerosol population in the CLOUD chamber for particles smaller than 10 nm at different temperatures. A more consistent picture emerged when we normalized the growth rates to a fixed gas-phase sulfuric acid concentration. All of the instruments detected larger growth rates at lower temperatures, and the observed growth rates decreased as a function of temperature, showing a similar trend for all instruments. The theoretical calculations had a similar but much smaller temperature dependency.
Large conurbations are a significant source of the anthropogenic pollution and demographic differences between cities that result in a different pollution burden. The metropolitan area of Sao Paulo ...(MASP, population 20 million) accounts for one fifth of the Brazilian vehicular fleet. A feature of MASP is the amount of ethanol used by the vehicular fleet, known to exacerbate air quality. The study describes the diurnal behaviour of the submicron aerosol and relies on total particle number concentration, particle number size distribution, light scattering and light absorption measurements. Modelled planetary boundary layer (PBL) depth and air mass movement data were used to aid the interpretation. During morning rush-hour, stagnant air and a shallow PBL height favour the accumulation of aerosol pollution. During clear-sky conditions, there was a wind shift towards the edge of the city indicating a heat island effect with implications on particulate pollution levels at the site. The median total particle number concentration for the submicron aerosol typically varied in the range 1.6 10 super(4)-3.2 10 super(4) cm super(-3) frequently exceeding 4 10 super(4) cm super(-3) during the day. During weekdays, nucleation-mode particles are responsible for most of the particles by numbers. The highest concentrations of total particle number concentrations and black carbon (BC) were observed on Fridays. Median diurnal values for light absorption and light scattering (at 637 nm wavelength) varied in the range 12-33 Mm super(-1) and 21-64 Mm super(-1), respectively. The former one is equal to 1.8-5.0 mu g m super(-3) of BC. The growth of the PBL, from the morning rush-hour until noon, is consistent with the diurnal cycle of BC mass concentrations. Weekday hourly median single-scattering albedo ( omega sub(0)) varied in the range 0.59-0.76. Overall, this suggests a top of atmosphere (TOA) warming effect. However, considering the low surface reflectance of urban areas, for the given range of omega sub(0), the TOA radiative forcing can be either positive or negative for the sources within the MASP. On the average, weekend omega sub(0) values were 0.074 higher than during weekdays. During 11% of the days, new particle formation (NPF) events occurred. The analysed events growth rates ranged between 9 and 25 nm h super(-1). Sulphuric acid proxy concentrations calculated for the site were less than 5% of the concentration needed to explain the observed growth. Thus, other vapours are likely contributors to the observed growth.
Recent studies have shown very high frequencies of atmospheric new particle formation in different environments in South Africa. Our aim here was to investigate the causes for two or three ...consecutive daytime nucleation events, followed by subsequent particle growth during the same day. We analysed 108 and 31 such days observed in a polluted industrial and moderately polluted rural environments, respectively, in South Africa. The analysis was based on two years of measurements at each site. After rejecting the days having notable changes in the air mass origin or local wind direction, i.e. two major reasons for observed multiple nucleation events, we were able to investigate other factors causing this phenomenon. Clouds were present during, or in between most of the analysed multiple particle formation events. Therefore, some of these events may have been single events, interrupted somehow by the presence of clouds. From further analysis, we propose that the first nucleation and growth event of the day was often associated with the mixing of a residual air layer rich in SO2 (oxidized to sulphuric acid) into the shallow surface-coupled layer. The second nucleation and growth event of the day usually started before midday and was sometimes associated with renewed SO2 emissions from industrial origin. However, it was also evident that vapours other than sulphuric acid were required for the particle growth during both events. This was especially the case when two simultaneously growing particle modes were observed. Based on our analysis, we conclude that the relative contributions of estimated H2SO4 and other vapours on the first and second nucleation and growth events of the day varied from day to day, depending on anthropogenic and natural emissions, as well as atmospheric conditions.
The significance of ion–ion recombination for atmospheric new particle formation is not well quantified. Here we present and evaluate a method for determining the size distribution of recombination ...products from the size distributions of neutral and charged clusters. Our method takes into account the production of recombination products in the collisions between oppositely charged ions and the loss due to coagulation. Furthermore, unlike previous studies, we also consider the effect of condensational growth on the size distribution of recombination products. We applied our method to the data measured in Hyytiälä, Finland, to estimate the contribution of ion–ion recombination to the concentrations of atmospheric clusters in the size range of 0.9–2.1 nm. We observed that the concentration of recombination products was highest in the size classes between 1.5 and 1.9 nm. The median concentrations of recombination products were between 6 and 69 cm−3 in different size classes, which resulted in a small proportion of all neutral clusters, varying between 0.2 and 13%. When examining the whole size range between 0.9 and 2.1 nm, the median fraction of recombination products of all neutral clusters was only 1.5%. We also investigated how the results change if the effect of condensational growth is neglected. It seems that with that assumption the fragmentation of newly formed recombination products has to be taken into account, or else the concentration of recombination products is overestimated. Overall, we concluded that our method provides reasonable results, which are consistent with the earlier estimates on the contribution of recombination products to atmospheric cluster population in Hyytiälä. Still, in order to determine the size distribution of recombination products more accurately in the future, more precise measurements of the size distribution of atmospheric clusters would be needed.
In this work, we examined the interaction of ions and neutral particles during atmospheric new particle formation (NPF) events. The analysis is based on simultaneous field measurements of atmospheric ...ions and total particles using a neutral cluster and air ion spectrometer (NAIS) across the diameter range 2–25 nm. The Waldstein research site is located in a spruce forest in NE Bavaria, Southern Germany, known for enhanced radon concentrations, presumably leading to elevated ionization rates. Our observations show that the occurrence of the ion nucleation mode preceded that of the total particle nucleation mode during all analyzed NPF events. The time difference between the appearance of 2 nm ions and 2 nm total particles was typically about 20 to 30 min. A cross correlation analysis showed a rapid decrease of the time difference between the ion and total modes during the growth process. Eventually, this time delay vanished when both ions and total particles did grow to larger diameters. Considering the growth rates of ions and total particles separately, total particles exhibited enhanced growth rates at diameters below 15 nm. This observation cannot be explained by condensation or coagulation, because these processes would act more efficiently on charged particles compared to neutral particles. To explain our observations, we propose a mechanism including recombination and attachment of continuously present cluster ions with the ion nucleation mode and the neutral nucleation mode, respectively.
In this study, we present our investigations on the counting efficiency of a TSI Environmental Particle Counter (EPC) Monitor Model 3783. The operation of the instrument is based on activation of ...sampled particles by water condensation, thus making it essentially a water-based condensation particle counter (WCPC). The counting efficiency was measured and simulated using different temperature settings on the conditioner and the growth tube, as well as using hygroscopic and water-soluble ammonium sulfate and sodium chloride particles, and insoluble and hydrophobic silver particles. The parameter that best describes the performance of the instrument is the cut-off diameter, or the diameter where 50% of sampled particles are activated and detected. In this study, the cut-off diameter for silver particles varied from 5.2 nm to 7.4 nm as a function of the temperature difference between the conditioner and the growth tube. The chemical composition and, specifically, the water solubility of particle components, had a significant effect on the counting efficiency. Using the standard operation settings of the EPC, the cut-off diameter for silver particles was 6.4 nm, and for ammonium sulfate and sodium chloride particles it was 4.8 nm and 4.3 nm, respectively. The simulations made with Comsol Multiphysics 3.5a simulation software gave the silver-water contact angle in the range of 29-45° depending on the temperature difference between the conditioner and the growth tube, and the effective contact angles of 25° and 21° for ammonium sulfate and sodium chloride particles.
Copyright 2013 American Association for Aerosol Research
As evidence of adverse health effects due to air pollution continues to increase, the World Health Organization (WHO) recently published its latest edition of the global air quality guidelines (World ...Health Organization, 2021). Although not legally binding, the guidelines aim to provide a framework in which policymakers can combat air pollution by formulating evidence-based air quality management strategies. In the light of this, the European Union has stated its intent to revise the current ambient air quality directive (2008/50/EC) to more closely resemble the newly published WHO guidelines (European Commission, 2020). This article provides an informed opinion on selected features of the air quality directive that we believe would benefit from a reassessment. The selected features include discussion about (1) air quality sensors as a part of a hierarchical observation network, (2) the number of minimum sampling points and their siting criteria, and (3) new target air pollution parameters for future consideration.
New particle formation (NPF) is a significant source of atmospheric
particles, affecting climate and air quality. Understanding the mechanisms
involved in urban aerosols is important to develop ...effective mitigation
strategies. However, NPF rates reported in the polluted boundary layer span
more than 4 orders of magnitude, and the reasons behind this variability are the subject of intense scientific debate. Multiple atmospheric vapours have been
postulated to participate in NPF, including sulfuric acid, ammonia, amines
and organics, but their relative roles remain unclear. We investigated NPF
in the CLOUD chamber using mixtures of anthropogenic vapours that simulate
polluted boundary layer conditions. We demonstrate that NPF in polluted
environments is largely driven by the formation of sulfuric acid–base
clusters, stabilized by the presence of amines, high ammonia concentrations
and lower temperatures. Aromatic oxidation products, despite their extremely
low volatility, play a minor role in NPF in the chosen urban environment but
can be important for particle growth and hence for the survival of newly
formed particles. Our measurements quantitatively account for NPF in highly
diverse urban environments and explain its large observed variability. Such
quantitative information obtained under controlled laboratory conditions
will help the interpretation of future ambient observations of NPF rates in
polluted atmospheres.
Condensable vapors, including highly oxygenated organic molecules
(HOMs), govern secondary organic aerosol formation and thereby impact the
quantity, composition, and properties (e.g., toxicity) of ...aerosol particles.
These vapors are mainly formed in the atmosphere through the oxidation of
volatile organic compounds (VOCs). Urban environments contain a variety of
VOCs from both anthropogenic and biogenic sources, as well as other species,
for instance nitrogen oxides (NOx), that can greatly influence the
formation pathways of condensable vapors like HOMs. During the last decade,
our understanding of HOM composition and formation has increased
dramatically, with most experiments performed in forests or in heavily
polluted urban areas. However, studies on the main sources for condensable
vapors and secondary organic aerosols (SOAs) in biogenically influenced urban
areas, such as suburbs or small cities, have been limited. Here, we studied
the HOM composition, measured with two nitrate-based chemical ionization
mass spectrometers and analyzed using positive matrix factorization (PMF),
during late spring at two locations in Helsinki, Finland. Comparing the
measured concentrations at a street canyon site and a nearby urban
background station, we found a strong influence of NOx on the HOM
formation at both stations, in agreement with previous studies conducted in
urban areas. Even though both stations are dominated by anthropogenic VOCs,
most of the identified condensable vapors originated from biogenic
precursors. This implies that in Helsinki anthropogenic activities mainly
influence HOM formation by the effect of NOx on the biogenic VOC
oxidation. At the urban background station, we found condensable vapors
formed from two biogenic VOC groups (monoterpenes and sesquiterpenes), while
at the street canyon, the only identified biogenic HOM precursor was
monoterpenes. At the street canyon, we also observed oxidation products of
aliphatic VOCs, which were not observed at the urban background station. The
only factors that clearly correlate (temporally and composition-wise)
between the two stations contained monoterpene-derived dimers. This suggests
that HOM composition and formation mechanisms are strongly dependent on
localized emissions and the oxidative environment in these biogenically
influenced urban areas, and they can also change considerably within
distances of 1 km within the urban environment. This further
suggests that studies should be careful when extrapolating single-point
measurements in an urban setting to be representative of district or city
scales.
Aerosol properties were studied during an intensive airborne measurement campaign that took place at Rotterdam in Netherlands in May 2008 within the framework of the European Aerosol Cloud Climate ...and Air Quality Interactions project (EUCAARI). The objective of this study is to illustrate seven events of new particle formation (NPF) observed with two Condensation Particle Counters (CPCs) operated on board the ATR-42 research aircraft in airsectors around Rotterdam, and to provide information on the spatial extent of the new particle formation phenomenon based on 1-s resolution measurements of ultra-fine particle (in the size range 3-10 nm diameter, denoted N3-10 hereafter) concentrations. The results show that particle production occurred under the influence of different air mass origins, at different day times and over the North Sea as well as over the continent. The number concentration of freshly nucleated particles (N3-10 ) varied between 5000 and 100 000 cm-3 within the boundary layer (BL). Furthermore the vertical extension for all nucleation events observed on the ATR-42 never exceeded the upper limit of the BL. The horizontal extent of N3-10 could not be delimited due to inflexible flight plans which could not be modified to accommodate real-time results. However, the NPF events were observed over geographically large areas; typically the horizontal extension was about 100 km and larger.
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