Total Aerosol Number Concentration Research Articles

Genesis of New Particle Formation Events in a Semi-Urban Location in Eastern Himalayan Foothills

New particle formation (NPF) events identified using scanning mobility particle sizer (SMPS) measurements, their subsequent growth and other characteristics over Dibrugarh, a semi-urban location in the eastern Himalayan foothills (EHF), during November–December 2016 are presented. The mean total number concentration of ultrafine aerosols was found to be high during morning and evening rush hours. The NPF occurrence frequency was found to be 14%. The temporal evolution of the hourly average aerosol number size distribution revealed that the nucleation burst occurred at a lower size spectrum, supporting the existence of NPF burst events. It continued to grow through coagulation loss and condensation sink with an average growth rate of 17.16 ± 12.29 nm/hr. The satellite-based observations showed a high concentration of the NPF precursors NO2, SO2, and HCHO during the NPF days. The backward air mass trajectories confirmed that the sources of emissions were confined within an area of radius ~100 km surrounding the observation site. These locally generated precursors and their associated photochemistry could be a probable reason for NPF occurrence at the study site.

Impact of monsoon on below cloud base aerosol hygroscopicity over a rain shadow region of India

Vertically constrained observations of aerosol size distribution and hygroscopicity using the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX) measurements during the monsoon seasons of 2018 and 2019 over a typical global climate model grid area are presented. Two regimes of aerosol loading - low and high, were identified within the season. Low aerosol loading is associated with active monsoon conditions and strong westerlies, while high aerosol loading occurs when the westerly airmass weakens or becomes continental. Aerosol hygroscopicity was the lowest (∼0.08) during low aerosol loading days in 2019 and the highest (∼0.3) during high aerosol loading days in 2018. Aitken mode aerosols control the bulk hygroscopicity on high aerosol loading days and at high supersaturation. The refractory Black Carbon (rBC) aerosols accounted for nearly 10% of the total aerosol number concentration during the monsoon. The internally mixed rBC aerosols had thicker coatings for smaller rBC cores and vice-versa. The cloud condensation nuclei (CCN) closure at the cloud base is established from the in situ observations. These observations are first-of-its-kind from the Indian region, covering two contrasting monsoon seasons, and are useful for studying aerosol-cloud interactions and constraining models.

Impact of Relative Humidity on the vertical distribution of aerosols over India

Water uptake by aerosol particles significantly changes its light-scattering characteristics, alters the physical and optical properties of aerosols. In this article, we present the effect of ambient relative humidity (RH) on the optical properties of surface and columnar aerosols under different RH conditions during different seasons over India. In particular, relation between surface RH and surface aerosol properties, surface RH and aerosol optical depth (AOD) and profile of RH on the AOD is presented. An increase in the surface aerosol scattering coefficient (σscat) and total aerosol number concentration (N(d)) is observed under high humidity (50–100%) condition than low humidity (0–30%). This is more prominent in the winter and pre-monsoon seasons. An increase in the AOD is observed as surface RH increase in all the seasons except in monsoon season where it showed an inverse relation. The profile measurements (Lidar and radiosonde) also showed a consistent increase in AOD (0-6 km) from low to high RH (0-6 km) conditions. This relationship is significant during winter followed by the post-monsoon, pre-monsoon, and monsoon seasons. An increase in AOD with RH is observed regardless of altitude in all seasons, except during the monsoon at higher altitudes (2-6 km). Our findings clearly demonstrated that during the winter and monsoon (pre- and post-monsoon) seasons, aerosols within (above) the boundary layer are more sensitive to the RH. This relationship has been tested in different surface conditions across India using CALIPSO and IMD radiosonde measurements. These measurements also confirmed an increase in AOD with increasing RH in all the regions except East Coast (EC) region. Irrespective of the region, this feature is more prominent at lower altitudes (0–1.5 km) during winter and higher altitudes (1.5-6 km) during other seasons. At higher altitudes, only a few regions (Central India, Indo-Gangetic Plain, and West Coast) showed an inverse relationship between AOD and RH during the monsoon and post-monsoon seasons. Further, our results illustrated the contribution of hygroscopic particles to the RH increases the AOD in a given season. This finding implies that hygroscopic growth caused by water-soluble particles in the lower troposphere can significantly alter the magnitude of aerosol radiative forcing both at the surface and at the top of the atmosphere.

Experimental development of a lake spray source function and its model implementation for Great Lakes surface emissions

Abstract. Lake spray aerosols (LSAs) are generated from freshwater breaking waves in a mechanism similar to their saltwater counterparts, sea spray aerosols (SSAs). Unlike the well-established research field pertaining to SSAs, studying LSAs is an emerging research topic due to their potential impacts on regional cloud processes and their association with the aerosolization of freshwater pathogens. A better understanding of these climatic and public health impacts requires the inclusion of LSA emission in atmospheric models, yet a major hurdle to this inclusion is the lack of a lake spray source function (LSSF), namely an LSA emission parameterization. Here, we develop an LSSF based on measurements of foam area and the corresponding LSA emission flux in a marine aerosol reference tank (MART). A sea spray source function (SSSF) is also developed for comparison. The developed LSSF and SSSF are then implemented in the Community Multiscale Air Quality (CMAQ) model to simulate particle emissions from the Great Lakes surface from 10 to 30 November 2016. Measurements in the MART revealed that the average SSA total number concentration was 8 times higher than that of LSA. Over the 0.01–10 µm aerosol diameter size range, the developed LSSF was around 1 order of magnitude lower than the SSSF and around 2 orders of magnitude lower for aerosols with diameters between 1 and 3 µm. Model results revealed that LSA emission flux from the Great Lakes surface can reach ∼105 m−2 s−1 during an episodic event of high wind speeds. These emissions only increased the average total aerosol number concentrations in the region by up to 1.65 %, yet their impact on coarse-mode aerosols was much more significant, with up to a 19-fold increase in some areas. The increase in aerosol loading was mostly near the source region, yet LSA particles were transported up to 1000 km inland. Above the lakes, LSA particles reached the cloud layer, where the total and coarse-mode particle concentrations increased by up to 3 % and 98 %, respectively. Overall, this study helps quantify LSA emission and its impact on regional aerosol loading and the cloud layer.

New particle formation in coastal New Zealand with a focus on open-ocean air masses

Abstract. Even though oceans cover the majority of the Earth, most aerosol measurements are from continental sites. We measured aerosol particle number size distribution at Baring Head, in coastal New Zealand, over a total period of 10 months to study aerosol properties and new particle formation, with a special focus on aerosol formation in open-ocean air masses. Particle concentrations were higher in land-influenced air compared to clean marine air in all size classes, from sub-10 nm to cloud condensation nuclei sizes. When classifying the particle number size distributions with traditional methods designed for continental sites, new particle formation was observed at the station throughout the year with an average event frequency of 23 %. While most of these traditional event days had some land influence, we also observed particle growth starting from nucleation mode in 16 % of the data in clean marine air, and at least part of this growth was connected to nucleation in the marine boundary layer. Sub-10 nm particles accounted for 29 % of the total aerosol number concentration of particles larger than 1 nm in marine air during the spring. This shows that nucleation in marine air is frequent enough to influence the total particle concentration. Particle formation in land-influenced air was more intense and had on average higher growth rates than what was found for marine air. Particle formation and primary emissions increased particle number concentrations as a function of time spent over land during the first 1–2 d. After this, nucleation seems to start getting suppressed by the pre-existing particle population, but accumulation mode particle concentration keeps increasing, likely due to primary particle emissions. Further work showed that traditional NPF events were favoured by sunny conditions with low relative humidity and wind speeds. In marine air, formation of sub-10 nm particles was favoured by low temperatures, relative humidity, and wind speeds and could happen even during the night. Our future work will study the mechanisms responsible for particle formation at Baring Head with a focus on different chemical precursor species. This study sheds light on both new particle formation in open-ocean air masses coming from the Southern Ocean and local aerosol properties in New Zealand.

Mesoscale variations of the chemical composition of submicron aerosols and its influence on the cloud condensation nuclei activation

Mesoscale variation of the chemical composition of submicron aerosol concentrations and their influence on cloud condensation nuclei (CCN) activation have been examined over a tropical coastal location in peninsular India during the winter season. The land-sea breeze circulation, boundary layer evolution, and photochemical processes significantly influence the diurnal variation of the aerosol chemical composition over the region. Broadly, the organic aerosols (mean ∼37.50 ± 27.00 μg m−3) dominated the submicron mass loading with a mass fraction (MF) of 0.66, followed by sulfate (∼10.92 ± 6.13 μg m−3; MF ∼0.19), ammonium (3.46 ± 1.71 μg m−3; MF∼0.06) and a small contribution from nitrate (1.7 ± 1.5 μg m−3; MF ∼0.03). The average mass concentration of organic carbon (OC) is 8.84 ± 6.42 μg m−3 with a mean organics/OC ratio of ∼3, indicating the presence of aged, highly oxidized organics. The diurnal variation of all the aerosol species, except sulfate, depicted daytime-low and nighttime-high. The photochemical formation of sulfate aerosols overwhelms the reduction in concentration due to boundary layer mixing and sea-land breeze circulation during the daytime. The decrease in the organics/sulfate ratio during the daytime has significant implications on the CCN concentration and its activation properties. The average CCN number concentration and activation ratio (ratio of CCN to total aerosol number concentration) at 0.38% supersaturation during the study period are ∼3756 ± 1609 cm−3 and 0.52 ± 0.17, respectively. The diurnal variation of CCN concentrations and activation ratio is distinctly different. The change in the mode diameter of the number size distribution between sea-land breeze was found to be less (∼8 nm) compared to the large variation in chemical composition. This suggested the importance of mesoscale variations of aerosols, especially the contrasting diurnal variation of organics and sulfate aerosols in CCN activation.

Elucidating local pollution and site representativeness at the Jungfraujoch, Switzerland through parallel aerosol measurements at an adjacent mountain ridge

Many long-term air pollution and climate monitoring stations face the issue of increasing anthropogenic activities in their vicinity. Furthermore, the spatial representativeness of the sites is often not entirely understood especially in mountainous terrain with complex topographic features. This study presents a 5-year comparison of parallel aerosol measurements (total particle number concentration and equivalent black carbon mass concentration) at the Jungfraujoch in the Swiss Alps (JFJ, 3580 m a.s.l.), and an adjacent mountain ridge, the Jungfrau East Ridge (JER, 3705 m a.s.l.), in 1000 m air-line distance to the main site. The parallel aerosol measurements reveal characteristic differences in the diurnal variations between the two sites under certain specific meteorological conditions. Our analysis estimates that on 20%–40% of the days local activities at the Jungfraujoch have a clear influence on the measured time series of the total aerosol number concentration and the equivalent black carbon mass concentration. This influence is mainly seen in form of strong isolated spikes rather than by an increase in the on-site background concentration. They can thus be flagged during the data quality assurance process and filtered from those measurement parameters available at high time resolution. Removing the spikes from the original time series results in daily mean values for the total aerosol number concentration and equivalent black carbon mass concentration that are 5%–10% lower compared to the original signals. During nighttime with hardly any local pollution sources that cause spikes this percentage decreases towards 0%. The signal baselines at the Jungfraujoch and Jungfrau East Ridge correlate well during more than 50% of the days.

New particle formation at urban and high-altitude remote sites in the south-eastern Iberian Peninsula

Abstract. A substantial fraction of the atmospheric aerosols originates from secondary new particle formation (NPF), where atmospheric vapours are transformed into particles that subsequently grow to larger sizes, affecting human health and the climate. In this study, we investigate aerosol size distributions at two stations located close to each other (∼ 20 km) but at different altitudes: urban (UGR; 680 m a.s.l., metres above sea level) and high-altitude remote (SNS; 2500 m a.s.l.) sites, both in the area of Granada, Spain, and part of AGORA observatory (Andalusian Global ObseRvatory of the Atmosphere). The analysis shows a significant contribution of nucleation mode aerosol particles to the total aerosol number concentration at both sites, with a contribution of 47 % and 48 % at SNS and UGR, respectively. Due to the important contribution of NPF events to the total aerosol number concentrations and their high occurrence frequency (> 70 %) during the study period, a detailed analysis of NPF events is done in order to get insight into the possible mechanisms and processes involved in NPF events at these contrastive sites. At SNS, NPF is found to be associated with the transport of gaseous precursors from lower altitudes by orographic buoyant upward flows. NPF events at the SNS site are always observed from the smallest measured sizes of the aerosol size distribution (4 nm), implying that NPF takes place in or in the vicinity of the high-altitude SNS station rather than being transported from lower altitudes. Although NPF events at the mountain site seem to be connected with those occurring at the urban site, growth rates (GRs) at SNS are higher than those at the UGR site (GR7−25 of 6.9 and 4.5 nm h−1 and GR4−7 of 4.1 and 3.6 nm h−1 at SNS and UGR, respectively). This fact could have special importance for the production of cloud condensation nuclei (CCN) and therefore for cloud formations which may affect regional/global climate, since larger GRs at mountain sites could translate to a larger survival probability of NPF particles reaching CCN sizes, due to the shorter time period needed for the growth. The analysis of sulfuric acid (H2SO4) shows that the contribution of H2SO4 is able to explain a minimal fraction contribution to the observed GRs at both sites (< 1 % and < 10 % for the 7–25 and 4–7 nm size ranges, respectively), indicating that other condensing vapours are responsible for the majority of particle growth, as well as the differing growth rates between the two sites. Results also show that the condensation sink (CS) does not play a relevant role in NPF processes at both sites and points to the availability of volatile organic compounds (VOCs) as one of the main factors controlling the NPF events at both sites. Finally, a closer analysis of the NPF events that were observed at the SNS site during a Saharan dust episode that occurred during the field campaign was carried out, evidencing the role of TiO2 and F2O3 together with VOCs in promoting new particle formation during this dust intrusion event. Although further investigation is needed to improve our understanding in this topic, this result suggests that climate effects of mineral dust and NPF are not disconnected from each other as it was commonly thought. Therefore, since mineral dust contributes to a major fraction of the global aerosol mass load, dust–NPF interaction should be taken into account in global aerosol-climate modelling for better climate change prediction.

Influx of African biomass burning aerosol during the Amazonian dry season through layered transatlantic transport of black carbon-rich smoke

Abstract. Black carbon (BC) aerosols influence the Earth's atmosphere and climate, but their microphysical properties, spatiotemporal distribution, and long-range transport are not well constrained. This study presents airborne observations of the transatlantic transport of BC-rich African biomass burning (BB) smoke into the Amazon Basin using a Single Particle Soot Photometer (SP2) as well as several complementary techniques. We base our results on observations of aerosols and trace gases off the Brazilian coast onboard the HALO (High Altitude and LOng range) research aircraft during the ACRIDICON-CHUVA campaign in September 2014. During flight AC19 over land and ocean at the northeastern coastline of the Amazon Basin, we observed a BC-rich layer at ∼3.5 km altitude with a vertical extension of ∼0.3 km. Backward trajectories suggest that fires in African grasslands, savannas, and shrublands were the main source of this pollution layer and that the observed BB smoke had undergone more than 10 d of atmospheric transport and aging over the South Atlantic before reaching the Amazon Basin. The aged smoke is characterized by a dominant accumulation mode, centered at about 130 nm, with a particle concentration of Nacc=850±330 cm−3. The rBC particles account for ∼15 % of the submicrometer aerosol mass and ∼40 % of the total aerosol number concentration. This corresponds to a mass concentration range from 0.5 to 2 µg m−3 (1st to 99th percentiles) and a number concentration range from 90 to 530 cm−3. Along with rBC, high cCO (150±30 ppb) and cO3 (56±9 ppb) mixing ratios support the biomass burning origin and pronounced photochemical aging of this layer. Upon reaching the Amazon Basin, it started to broaden and to subside, due to convective mixing and entrainment of the BB aerosol into the boundary layer. Satellite observations show that the transatlantic transport of pollution layers is a frequently occurring process, seasonally peaking in August/September. By analyzing the aircraft observations together with the long-term data from the Amazon Tall Tower Observatory (ATTO), we found that the transatlantic transport of African BB smoke layers has a strong impact on the northern and central Amazonian aerosol population during the BB-influenced season (July to December). In fact, the early BB season (July to September) in this part of the Amazon appears to be dominated by African smoke, whereas the later BB season (October to December) appears to be dominated by South American fires. This dichotomy is reflected in pronounced changes in aerosol optical properties such as the single scattering albedo (increasing from 0.85 in August to 0.90 in November) and the BC-to-CO enhancement ratio (decreasing from 11 to 6 ng m−3 ppb−1). Our results suggest that, despite the high fraction of BC particles, the African BB aerosol acts as efficient cloud condensation nuclei (CCN), with potentially important implications for aerosol–cloud interactions and the hydrological cycle in the Amazon.

On the submicron aerosol distributions and CCN activity in and around the Korean Peninsula measured onboard the NASA DC-8 research aircraft during the KORUS-AQ field campaign

Aerosol and CCN number concentrations, and aerosol size distributions in and around the Korean Peninsula were measured onboard the NASA DC-8 research aircraft during the KORUS-AQ campaign in May and June of 2016. The average and standard deviation values of total aerosol number concentrations (diameter > 10 nm, NCN10) in the boundary layer (below 1 km altitude) over Seoul, the Korean Peninsula, the Yellow Sea, the East Sea, and the South Sea were 12,318±7808, 10,721±8636, 7599±8583, 5759±6051, and 4186±4777 cm−3, respectively. Corresponding values for CCN number concentration at 0.6% supersaturation (NCCN06) were 3358±1916, 3613±2242, 3422±1707, 2313±1039, and 1819±1328 cm−3, respectively. NCN10 was highly variable according to region and period. In contrast, NCCN06 was relatively invariant regardless of region and period. With the PMF analysis on the aircraft measured aerosol size distribution and NCCN06 data, it was found that aerosol size distributions were composed of several distinct modes and they were different depending on regions. The aerosol hygroscopicity parameter κ was also estimated based on the PMF analysis results. The estimated κ values over Seoul, the Korean Peninsula, and the Yellow Sea were 0.11, 0.11, and 0.36, respectively. Lastly, the CCN closure experiments indicated that CCN concentration could be successfully estimated with the aerosol size distribution data and the estimated κ information from the aircraft measurements. Overall, it was demonstrated that PMF analysis technique could be applied to extract valuable information from limited aircraft measurement dataset.

Quantifying aerosol size distributions and their temporal variability in the Southern Great Plains, USA

Abstract. A quality-controlled, 5-year dataset of aerosol number size distributions (particles with diameters (Dp) from 7 nm through 14 µm) was developed using observations from a scanning mobility particle sizer, aerodynamic particle sizer, and a condensation particle counter at the Department of Energy's Southern Great Plains (SGP) site. This dataset was used for two purposes. First, typical characteristics of the aerosol size distribution (number, surface area, and volume) were calculated for the SGP site, both for the entire dataset and on a seasonal basis, and size distribution lognormal fit parameters are provided. While the median size distributions generally had similar shapes (four lognormal modes) in all the seasons, there were some significant differences between seasons. These differences were most significant in the smallest particles (Dp<30 nm) and largest particles (Dp>800 nm). Second, power spectral analysis was conducted on this long-term dataset to determine key temporal cycles of total aerosol concentrations, as well as aerosol concentrations in specified size ranges. The strongest cyclic signal was associated with a diurnal cycle in total aerosol number concentrations that was driven by the number concentrations of the smallest particles (Dp<30 nm). This diurnal cycle in the smallest particles occurred in all seasons in ∼50 % of the observations, suggesting a persistent influence of new particle formation events on the number concentrations observed at the SGP site. This finding is in contrast with earlier studies that suggest new particle formation is observed primarily in the springtime at this site. The timing of peak concentrations associated with this diurnal cycle was shifted by several hours depending on the season, which was consistent with seasonal differences in insolation and boundary layer processes. Significant diurnal cycles in number concentrations were also found for particles with Dp between 140 and 800 nm, with peak concentrations occurring in the overnight hours, which were primarily associated with both nitrate and organic aerosol cycles. Weaker cyclic signals were observed for longer timescales (days to weeks) and are hypothesized to be related to the timescales of synoptic weather variability. The strongest periodic signals (3.5–5 and 7 d cycles) for these longer timescales varied depending on the season, with no cyclic signals and the lowest variability in the summer.

Quantifying the aerosol effect on droplet size distribution at cloud top

Abstract. This work uses the number concentration-effective diameter phase-space to test cloud sensitivity to variations in the aerosol population characteristics, such as the aerosol size distribution, number concentration and hygroscopicity. It is based on the information from the top of a cloud simulated by a bin-microphysics single-column model, for initial conditions typical of the Amazon, using different assumptions regarding the entrainment and the aerosol size distribution. It is shown that the cloud-top evolution can be very sensitive to aerosol properties, but the relative importance of each parameter is variable. The sensitivity to each aerosol characteristic varies as a function of the parameter tested and is conditioned by the base values of the other parameters, showing a specific dependence for each configuration of the model. When both the entrainment and the bin treatment of the aerosol are allowed, the largest influence on the droplet size distribution sensitivity was obtained for the median radius of the aerosols and not for the total number concentration of aerosols. Our results reinforce that the cloud condensation nuclei activity can not be predicted solely on the basis of the w∕Na supersaturation-based regimes.

Arctic marine secondary organic aerosol contributes significantly to summertime particle size distributions in the Canadian Arctic Archipelago

Abstract. Summertime Arctic aerosol size distributions are strongly controlled by natural regional emissions. Within this context, we use a chemical transport model with size-resolved aerosol microphysics (GEOS-Chem-TOMAS) to interpret measurements of aerosol size distributions from the Canadian Arctic Archipelago during the summer of 2016, as part of the “NETwork on Climate and Aerosols: Addressing key uncertainties in Remote Canadian Environments” (NETCARE) project. Our simulations suggest that condensation of secondary organic aerosol (SOA) from precursor vapors emitted in the Arctic and near Arctic marine (ice-free seawater) regions plays a key role in particle growth events that shape the aerosol size distributions observed at Alert (82.5∘ N, 62.3∘ W), Eureka (80.1∘ N, 86.4∘ W), and along a NETCARE ship track within the Archipelago. We refer to this SOA as Arctic marine SOA (AMSOA) to reflect the Arctic marine-based and likely biogenic sources for the precursors of the condensing organic vapors. AMSOA from a simulated flux (500 µgm-2day-1, north of 50∘ N) of precursor vapors (with an assumed yield of unity) reduces the summertime particle size distribution model–observation mean fractional error 2- to 4-fold, relative to a simulation without this AMSOA. Particle growth due to the condensable organic vapor flux contributes strongly (30 %–50 %) to the simulated summertime-mean number of particles with diameters larger than 20 nm in the study region. This growth couples with ternary particle nucleation (sulfuric acid, ammonia, and water vapor) and biogenic sulfate condensation to account for more than 90 % of this simulated particle number, which represents a strong biogenic influence. The simulated fit to summertime size-distribution observations is further improved at Eureka and for the ship track by scaling up the nucleation rate by a factor of 100 to account for other particle precursors such as gas-phase iodine and/or amines and/or fragmenting primary particles that could be missing from our simulations. Additionally, the fits to the observed size distributions and total aerosol number concentrations for particles larger than 4 nm improve with the assumption that the AMSOA contains semi-volatile species: the model–observation mean fractional error is reduced 2- to 3-fold for the Alert and ship track size distributions. AMSOA accounts for about half of the simulated particle surface area and volume distributions in the summertime Canadian Arctic Archipelago, with climate-relevant simulated summertime pan-Arctic-mean top-of-the-atmosphere aerosol direct (−0.04 W m−2) and cloud-albedo indirect (−0.4 W m−2) radiative effects, which due to uncertainties are viewed as an order of magnitude estimate. Future work should focus on further understanding summertime Arctic sources of AMSOA.

Features of Diurnal Variability of Ultrafine Aerosol in the Air of the Baikal Coastal Zone and Arid Zone of Mongolia

The results of an experimental study of ultrafine aerosol characteristics in the Baikal region and the Gobi Desert are described. The comparative analysis of the dispersion composition of atmospheric aerosol in different climate conditions is carried out. It is ascertained that the total content of ultrafine aerosol in the atmosphere of the Gobi Desert is significantly lower than in the Baikal atmosphere and soil aerosols prevail. In the Lake Baikal region, nanometer-size aerosols are also present, mainly of anthropogenic and organic origin; two peaks are observable in the diurnal variations in the total number concentration of aerosols in the afternoon and evening. In the morning and afternoon, the number of nucleation-mode particles increases due to intensification of breeze circulation, which promotes transport of anthropogenic impurities from the lake and activation of photochemical reactions.

Design and Performance Evaluation of a PN1 Sensor for Real-Time Measurement of Indoor Aerosol Size Distribution

Airborne particulate matter is an important factor in the quality of an indoor environment. In this study, a miniaturized particle sensor was developed to detect submicron-sized aerosols based on number counting. This particle number (PN) sensor was designed and fabricated for real-time measurement of total aerosol number concentration and geometric mean diameter. The sensor (hereafter called as PN1 sensor) comprised a particle-classification unit, a particle-charging unit, and a particle-detection unit. After integrating all the three units, the total number concentration and the geometric mean diameter of test aerosol particles were determined and the results were compared with those obtained using commercial instruments. First, the PN1 sensor was compared with a condensation particle counter (CPC) in lab-test. For this, different groups of monodisperse sodium chloride particles between 20 and 700 nm in diameter were used. Then the PN1 sensor was compared with a scanning mobility particle sizer (SMPS) and an aerodynamic particle sizer (APS). For this, the PN1 sensor data were obtained by varying the combination of two corona voltage and test particles (sodium chloride and polystyrene latex) size distribution. In addition to lab-test, field test was carried out with indoor aerosols in different places. The number concentration and geometric mean diameter of indoor aerosols were measured by PN1 sensor and compared with SMPS data. The number concentration was also compared with the results of CPC and Pegasor AQ Indoor (Pegasor, Finland) measurements.

Aerosol Properties Observed in the Subtropical North Pacific Boundary Layer

AbstractThe impact of anthropogenic aerosol on climate forcing remains uncertain largely due to inadequate representation of natural aerosols in climate models. The marine boundary layer (MBL) might serve as a model location to study natural aerosol processes. Yet source and sink mechanisms controlling the MBL aerosol number, size distribution, chemical composition, and hygroscopic properties remain poorly constrained. Here aerosol size distribution and water uptake measurements were made aboard the R/V Hi'ialakai from 27 June to 3 July 2016 in the subtropical North Pacific Ocean. Size distributions were predominantly bimodal with an average integrated number concentration of 197 ± 98 cm−3. Hygroscopic growth factors were measured using the tandem differential mobility analyzer technique for dry 48, 96, and 144 nm particles. Mode kappa values for these were 0.57 ± 0.12, 0.51 ± 0.09, and 0.52 ± 0.08, respectively. To better understand remote MBL aerosol sources, a new algorithm was developed which decomposes hygroscopicity distributions into three classes: carbon‐containing particles, sulfate‐like particles, and sodium‐containing particles. Results from this algorithm showed low and steady sodium‐containing particle concentrations while the sulfate‐like and carbon‐containing particle concentrations varied during the cruise. According to the classification scheme, carbon‐containing particles contributed at least 3–7%, sulfate‐like particles contributed at most 77–88% and sodium‐containing particles at least contributed 9–16% to the total aerosol number concentration. Size distribution and hygroscopicity data, in conjunction with air mass back trajectory analysis, suggested that the aerosol budget in the subtropical North Pacific MBL may be controlled by aerosol entrainment from the free troposphere.

Ground level ice nuclei particle measurements including Saharan dust events at a Po Valley rural site (San Pietro Capofiume, Italy)

Filter-collected aerosol samples in the PM1 and PM10 fractions and particle number concentration were measured during experimental campaigns in a rural area near Bologna (Italy) in the periods 10–21 February 2014 and 19–30 May 2014. Ice nuclei particle (INP) concentrations measured off-line showed prevalently higher average values in the morning with respect to the afternoon, in the PM1 fraction with respect to PM1–10 (with the exception of the first campaign, at Sw=1.01), and at water saturation ratio Sw=1.01 with respect to Sw=0.96.The aerosol in the coarse size range (1–10μm) contributed significantly to the total INP concentration. In the first campaign, the average INP concentration in the coarse fraction was 80% of the total in the morning and 74% in the afternoon, at Sw=1.01. In the second campaign, the contribution of the coarse size fraction to the INP number concentration was lower. On the whole, the results showed that the freezing activity of aerosol diameters larger than 1μm needs to be measured to obtain the entire INP population.Sahara dust events (SDEs) took place during both campaigns, in the periods 17–20 February and 21–23 May 2014. Results show that the averaged particle number concentration was higher during SDE than during no-Saharan dust events. A low correlation between INP and total aerosol number concentration was generally measured, except for SDEs observed in February, in which the correlation coefficient between aerosol concentration in the coarse fraction and INP in the same range, at water supersaturation, was about 0.8.Precipitation events influenced the aerosol concentration. In the February campaign, lower values of INP and particle concentrations were measured in case of heavy rain events. During the May campaign, an average number concentration of the aerosol in the range 0.5–10μm was slightly higher than on days when no precipitation was measured, the rainfall intensity being low. Only in a few cases did we note a sharp drop in INP in the PM10 fraction at Sw=1.01 (26 May, 8a.m. and 1p.m.; 27 May, 1p.m.).

Performance of a pilot-scale wet electrostatic precipitator for the control of sulfuric acid mist.

The use of a wet electrostatic precipitator (WESP) is often regarded as a viable option to reduce sulfuric acid mist emitted from the wet flue gas desulfurization (WFGD) tower in coal-fired power plants. In this study, a pilot-scale wet electrostatic precipitator equipped with a wall-cooled collection electrode is investigated for the control of sulfuric acid mist from a simulated WFGD system. The results show that due to partial charging effect, the removal efficiency of sulfuric acid aerosol decreases when the aerosol size decreases to several tens of nanometers. Moreover, due to the plasma-induced effect, a large number of ultrafine sulfuric acid aerosols below 50nm formed at a voltage higher than 24kV inside the WESP. The percentages of submicron-sized aerosols significantly increase together with the voltage. To minimize the adverse plasma-induced effect, a WESP should be operated at a high gas velocity with an optimum high voltage. Even at a high flue gas velocity of 2.3ms(-1), the mass concentration and the total number concentration of uncaptured sulfuric acid aerosols at the WESP outlet are as low as ca. 0.6mgm(-3) and ca. 10(4) 1cm(-3) at 28kV, respectively. The corresponding removal efficiencies were respectively higher than 99.4 and 99.9% and are very similar to that at 1.1 and 1.6ms(-1). Moreover, the condensation-induced aerosol growth enhances the removal of sulfuric acid mist inside a WESP and enables a low emission concentration of ca. 0.65mgm(-3) with a corresponding removal efficiency superior to 99.4% even at a low voltage of 21kV, and of ca. 0.35mgm(-3) with a corresponding removal efficiency superior to 99.6% at a higher voltage level of 26kV.

Investigation of a pilot-scale wet electrostatic precipitator for the control of sulfuric acid mist from a simulated WFGD system

Wet electrostatic precipitator (WESP) was often regarded as an effective countermeasure for sulfuric acid mist emitted from coal-fired power plants. However, recent studies indicate that WESP is an ambivalent measure due to its negative effect of generating ultrafine aerosols, which could lead to non-negligible solvent emission from amine based post-combustion capture (PPC) device. In this study, we attempt to clearly reveal how the key parameters, i.e. operating voltage and flue gas velocity, affected these ultrafine aerosols formation inside a pilot WESP. Our investigations have shown that a large number of ultrafine sulfuric acid aerosols formed in the WFGD process, with a cumulative size distribution (CSD) percentage close to 100% for aerosols below 150nm. With the activation of WESP, size distribution of sulfuric acid aerosol shifted towards smaller size. Especially, the percentages of submicron-sized aerosols were significantly increased with the increase of applied voltage. Our results confirmed that plasma-induced effect inside WESP was mainly responsible for ultrafine sulfuric acid aerosol formation, and indicated that its effect was weakening with increasing flue gas velocity. For further decreasing the plasma-induce effect, the investigated WESP was more suitable for operating at a high flue gas velocity with an optimum high voltage level, which could achieve better effect on energy utilization and aerosol control based on both number concentration and mass concentration. The results indicated that at a high flue gas velocity of 2.28m/s and a specific energy input (SEI) of 2.4kWh/1000m3, the mass concentration of sulfur trioxide and total number concentration of sulfuric acid aerosols at the investigated WESP outlet were as low as ~1.0mg/m3 and ~1041/cm3, respectively.

Aerosol size distribution seasonal characteristics measured in Tiksi, Russian Arctic

Abstract. Four years of continuous aerosol number size distribution measurements from the Arctic Climate Observatory in Tiksi, Russia, are analyzed. Tiksi is located in a region where in situ information on aerosol particle properties has not been previously available. Particle size distributions were measured with a differential mobility particle sizer (in the diameter range of 7–500 nm) and with an aerodynamic particle sizer (in the diameter range of 0.5–10 μm). Source region effects on particle modal features and number, and mass concentrations are presented for different seasons. The monthly median total aerosol number concentration in Tiksi ranges from 184 cm−3 in November to 724 cm−3 in July, with a local maximum in March of 481 cm−3. The total mass concentration has a distinct maximum in February–March of 1.72–2.38 μg m−3 and two minimums in June (0.42 μg m−3) and in September–October (0.36–0.57 μg m−3). These seasonal cycles in number and mass concentrations are related to isolated processes and phenomena such as Arctic haze in early spring, which increases accumulation and coarse-mode numbers, and secondary particle formation in spring and summer, which affects the nucleation and Aitken mode particle concentrations. Secondary particle formation was frequently observed in Tiksi and was shown to be slightly more common in marine, in comparison to continental, air flows. Particle formation rates were the highest in spring, while the particle growth rates peaked in summer. These results suggest two different origins for secondary particles, anthropogenic pollution being the important source in spring and biogenic emissions being significant in summer. The impact of temperature-dependent natural emissions on aerosol and cloud condensation nuclei numbers was significant: the increase in both the particle mass and the CCN (cloud condensation nuclei) number with temperature was found to be higher than in any previous study done over the boreal forest region. In addition to the precursor emissions of biogenic volatile organic compounds, the frequent Siberian forest fires, although far away, are suggested to play a role in Arctic aerosol composition during the warmest months. Five fire events were isolated based on clustering analysis, and the particle mass and cloud condensation nuclei number were shown to be somewhat affected by these events. In addition, during calm and cold months, aerosol concentrations were occasionally increased by local aerosol sources in trapping inversions. These results provide valuable information on interannual cycles and sources of Arctic aerosols.