Aerosol Size Distribution Measurements Research Articles

Establishing the contribution of lawn mowing to atmospheric aerosol levels in American suburbs

Abstract. Green leaf volatiles (GLVs) are a class of wound-induced volatile organic compounds emitted by several plant species. Turf grasses emit a complex profile of GLVs upon mowing, as evidenced by the "freshly cut grass" smell, some of which are readily oxidized in the atmosphere to contribute to secondary organic aerosol (SOA). The contribution of lawn-mowing-induced SOA production may be especially impactful at the urban–suburban interface, where urban hubs provide a source of anthropogenic oxidants and SOA while suburban neighborhoods have the potential to emit large quantities of reactive, mow-induced GLVs. This interface provides a unique opportunity to study aerosol formation in a multicomponent system and at a regionally relevant scale. Freshly cut grass was collected from a study site in Essex Junction, Vermont, and was placed inside a 775 L Teflon experimental chamber. Thermal desorption gas chromatography–mass spectrometry (TD-GC/MS) was used to characterize the emitted GLV profile. Ozone was introduced to the experimental chamber and TD-GC/MS was used to monitor the consumption of these GLVs and the subsequent evolution of gas-phase products, while a scanning mobility particle sizer was used to continuously measure aerosol size distributions and mass loadings as a result of grass clipping ozonolysis. Freshly cut grass was found to emit a complex mixture of GLVs, dominated by \\textit{cis}-3-hexenyl acetate (CHA) and \\textit{cis}-3-hexenol (HXL), which were released at an initial rate of 1.8 (± 0.5) μg and 0.07 (± 0.03) μg per square meter of lawn mowed with each mowing. Chamber studies using pure standards of CHA and HXL were found to have aerosol yields of 1.2 (± 1.1)% and 3.3 (± 3.1)%, respectively. Using these aerosol yields and the emission rate of CHA and HXL by grass, SOA evolution by ozonolysis of grass clippings was predicted. However, the measured SOA mass produced from the ozonolysis of grass clippings exceeded the predicted amount, by upwards of ~150%. The ozonolysis of a mixture of CHA and HXL representative of environmental mixing ratios also failed to accurately model the SOA mass produced by grass clippings. The disparity between measured SOA mass and the predicted SOA mass suggests that grass clippings contain other SOA precursors in addition to CHA and HXL. Aerial photographs and geospatial analysis were used to determine the area of turfgrass coverage in a suburban neighborhood, which was then used along with measured SOA production as a function of grass mowed to determine that lawn mowing has the potential to contribute 47 μg SOA per m−2 of lawn to the atmosphere per mowing event by ozonolysis, which cannot be modeled solely by the ozonolysis of CHA, HXL or a representative mixture of the two.

Seasonal and vertical variations in aerosol distribution over Shijiazhuang, China

To obtain a representative sampling of aerosol vertical profiles, we performed an extensive airborne characterization of aerosols under different environmental conditions over Shijiazhuang, China. Surface aerosol concentration and aerosol vertical distribution were analyzed using a set of 104 vertical profiles of aerosol number concentration and size distribution ranging from 0.1 to 3 μm observed by PCASP-100X. A four modal lognormal size distribution with 10-based logarithm was applied to fit measured aerosol size distributions at different altitudes of three seasons (spring, summer and autumn). It was found that the surface aerosol number concentration had a negative correlation with wind speed. In addition to wet removal of aerosols owing to precipitation in summer, vertical transport of aerosols from the surface to high levels is strongly influenced by convective instability, which contributes to the seasonality of aerosol vertical profiles. The aerosol vertical profiles under a wide range of synoptic conditions can be categorized as “ED” (exhibiting an exponential declining tendency with altitude), “SAL” (aerosol layers existing near surface), and “BAL” (aerosol layers at the boundary layer height). The multi-lognormal fitting captures the total aerosol number size distribution at 0.1–3 μm reasonably well. The average scale height of aerosols during spring, summer and autumn is 1.0 km, 1.6 km and 1.0 km, respectively.

Investigation of fine particulate pollution in a coastal city with a mobile monitoring platform

Abstract Spatial and temporal variation of fine particulate pollution in a complex small coastal city, Macau, was investigated by using a mobile air quality monitoring platform. Real-time street level measurements of aerosol size distribution were carried out three times per day by using an on-board wide-range particle spectrometer along a designed route covering the main area of the city for one week. The measured distributions were then transformed into PM2.5 mass concentrations for assessment based on an empirical relation estimated from a co-located measurement calibration process. Within this week, the averaged PM2.5 mass concentrations of the morning, afternoon, and evening sessions are 51.76 μg m-3, 28.87 μg m-3 and 30.77 μg m-3, respectively. By comparing the spatial statistics of the estimated PM2.5 concentrations with the US 24-hour primary NAAQS as a reference, a significant probability of exceedance (> 86%) was observed in 1/3 of the monitoring sessions, particularly in the morning of high traffic volume. Meanwhile, majority of the hotspots were found in the districts of the Macau peninsula. In addition, by performing analysis of the backward trajectories, daily MODIS images, and comparison of the PM2.5 patterns of the entire route of three selected measuring sessions during weekdays and weekend, it was observed that long range transport of fine particulates may affect Macau in a larger scale. Therefore, regional land source influence could shadow the local one when the ambient conditions are met.

Influence of continental outflow and ocean biogeochemistry on the distribution of fine and ultrafine particles in the marine atmospheric boundary layer over Arabian Sea and Bay of Bengal

Extensive measurements of aerosol number size distributions (in the size range of 10 to 875 nm) carried out over the oceanic regions of the Bay of Bengal and Arabian Sea during two large cruise experiments (one during pre‐monsoon and the other during winter) are used to investigate the spatial distribution of aerosol size distributions, in general, and that of fine particles, in particular, within the marine atmospheric boundary layer. The size distributions over the northwestern Bay of Bengal, lying downwind of the continental outflow from the Indo‐Gangetic Plain, and over the eastern Bay of Bengal, under the influence of the East Asian outflow, showed a bimodal structure with prominent mode (100–125 nm) in the accumulation regime and weak mode (30–40 nm) in the Aitken regime during both pre‐monsoon and winter seasons. While the Aitken mode was found to be relatively quite weak in the Indo‐Gangetic Plain outflow during both seasons, it was prominent in the East Asian outflow regions, especially during the winter season. The distributions over the northern Arabian Sea, a region quite prone to advection of dust during pre‐monsoon and summer seasons, showed a prominent Aitken mode (~45 nm) followed by a weaker accumulation mode during pre‐monsoon season. Analysis of SeaWiFS data revealed a systematic collocation of Aitken mode aerosols and the high chlorophyll concentration in the northern Arabian Sea, implying the role of ocean biogeochemistry in influencing the aerosol size distributions. Such a feature implying biogeochemical influence was not seen over the eastern and northern Bay of Bengal during pre‐monsoon and winter seasons.

CCN closure results from Indian Continental Tropical Convergence Zone (CTCZ) aircraft experiment

In-situ aircraft measurements of cloud condensation nuclei (CCN) and aerosol size distribution were carried out over the region spanning from 24.78 °N to 29.5 °N and 78.1 °E to 85.0 °E from June 29 to July 3, 2009 during the Indian Continental Tropical Convergence Zone (CTCZ) campaign, consisting of total 9 flight sorties. CCN measurements were conducted at a constant supersaturation (SS) of 0.84%. It was found that at higher altitudes (4.7–6.7km), 30nm sized particles were dominating while at lower altitudes (0.6–3.7km), 50nm particles. Overall, CCN closure ratio (CCNpredicted/CCNmeasured) at different altitudes using Köhler theory and assuming pure ammonium sulfate was 1.375 (R2=0.80). For each sortie, the closure ratio varied with height and depended greatly on measured CN concentrations. A case study of Khajuraho sortie showed that the closure ratio increased from 1.07 to 1.40 as the CCN concentration increased from 1000cm−3 to 4000cm−3. Results of CCN closure improved significantly (overprediction improved by 37.5% and 34.6% for Pantnagar and Gaya, respectively) with the assumption of internally mixed aerosols composed of ammonium sulfate and insoluble organics. Hygroscopicity parameter calculated for these two sorties (κ=0.51 and 0.5) indicates the presence of moderately hygroscopic organic species along with some inorganic content.

The mathematical principles and design of the NAIS – a spectrometer for the measurement of cluster ion and nanometer aerosol size distributions

Abstract. The paper describes the Neutral cluster and Air Ion Spectrometer (NAIS) – a multichannel aerosol instrument capable of measuring the distribution of ions (charged particles and cluster ions) of both polarities in the electric mobility range from 3.2 to 0.0013 cm2 V−1 s−1 and the distribution of aerosol particles in the size range from 2.0 to 40 nm. We introduce the principles of design, data processing and spectrum deconvolution of the instrument.

Aerosol dynamics upon Terni basin (Central Italy): results of integrated vertical profile measurements and electron microscopy analyses

In this work, aerosol size distribution measurements along with individual particle analyses were performed along the vertical profile in the atmosphere, to shed some light on the dynamics of evolution of aerosol properties upon a basin valley. The case study is the Terni basin, one of the most polluted urban and industrial sites in central Italy. Aerosol vertical profile measurements were performed using a helium-filled tethered balloon equipped with an optical particle counter (OPC), a miniaturized cascade impactor with particle collection filter, and a portable meteorological station. Combined OPC number size measurements and single particle analyses by scanning electron microscopy were employed to reconstruct the pattern and evolution of aerosol properties over the basin. Moreover, the CHIMERE chemistry-transport model was applied over a selected computing domain to obtain a general overview of the driving forces of the aerosol dynamics. Scanning electron microscopy methods along with chemical transport modeling revealed distinct distributions of number, size and geochemical properties of different particles classes in the aerosols. These reflect distinct behaviours and spatial/temporal evolution of the constituent particles, along with the common occurrence of dust inputs from regional to long range sources (e.g., Saharan dust inputs). All these features have to be taken into consideration when approaching the modeling of atmospheric processes, particularly in basin valleys located in Central and Southern Italy where the influence of Saharan dust outbreaks is more pronounced.

Distribution of ozone in the marine boundary layer of Arabian Sea prior to monsoon: Prevailing airmass and effect of aerosols

Surface ozone (O3) measurements were carried out in the marine environment of the Arabian Sea (AS) during the premonsoon months, April–May 2006, as part of the Integrated Campaign for Aerosols, gases and Radiation Budget. The O3 mixing ratio over the AS varied in the range ∼3–22 ppb with a mean of 13.5 ± 2 ppb. Comparatively high mixing ratios were observed over the southern AS and close to the coast. The spatial pattern did not show any evidence of transport from nearby landmass or in situ photochemistry. Longitudinally separated narrow regions of low and high O3 were seen over the southern AS. The role of aerosols in modifying the O3 concentration was examined based on the co-located measurement of aerosol mass loading, number density, size distribution and optical depth. The O3 mixing ratio showed positive correlation with aerosol loading. Over high O3 regions, large particle concentration showed significant enhancement. The role of chloride ion in depleting O3 was also investigated. The observed spatial features were compared with those measured during the earlier cruises conducted in different seasons and over various oceanic regions. A comparison has been made with the measurements over the Bay of Bengal during the same cruise.

Observation of new particle formation and growth events in Asian continental outflow

This study is based on 3-year continuous measurements (January 2008–December 2010) of aerosol number size distributions recorded with a Scanning Mobility Particle Sizer (SMPS) at two regional background stations, Gosan Climate Observatory (GCO) and Korea Global Atmosphere Watch Center (KGAWC), in Korea. We identified new particle formation and growth (NPF) events by applying the Cyclostationary Empirical Orthogonal Function (CSEOF) technique to aerosol number size distributions. Based on the first mode loading vectors and the corresponding principle components in the CSEOF analysis, we classified strong, weak, and non NPF days. A strong NPF event was observed on 7.5% of days (60 days out of a total 800 days) at GCO and on 14.6% of days (140 days out of a total 958 days) at KGAWC. The maximum occurrence of strong NPF events was reported in spring at GCO, but in winter at KGAWC. Only 16 of these days were considered as simultaneous NPF events, and 7 days were identical NPF events. The airmass history analysis on simultaneous NPF days indicated the NPF events to be associated with a fast-moving cold and dry airmass from the Asian continent after the passage of a frontal system. The particle formation rate (FR) and growth rate (GR) were estimated to be 1.44 (1.20) cm−3 s−1 and 4.4 (4.7) nm h−1, respectively, at GCO and KGAWC (in parentheses). Almost identical values for the condensation sink were estimated in strong NPF (8.3 × 10−3 s−1) and non NPF (8.2 × 10−3 s−1) events at GCO, whereas the condensation sink for strong NPF days (8.5 × 10−5 s−1) was lower than that of non NPF days (1.1 × 10−2 s−1) at KGAWC. The FR, GR, condensation sink, and vapor source rate at both GCO and KGAWC were lower than those reported in polluted urban areas, but higher than those at clean sites.

Aerosol properties over two urban sites in South Spain during an extended stagnation episode in winter season

Columnar and ground level aerosol properties as well as mass concentrations of some gaseous pollutants were measured at two urban sites (Granada and Málaga, South Spain) before, during and after an extended stagnation episode from 7 to 13 February 2011. This long lasting event was associated with a very strong and persistent blocking high-pressure system over the Iberian Peninsula, together with very intense and persistent temperature inversions near the ground level. The columnar aerosol load at Granada showed a significant increase during this stagnation episode as indicated by aerosol optical depth at 440 nm, reaching values four times higher (0.6) than before and after the event. A significant increase in aerosol load at night time was also evidenced by star photometer measurements. Similarly, pronounced enhancement in columnar aerosol load was observed at Málaga, indicating the regional extension of this event. Analysis of ground level measurements obtained at Granada showed a significant increase in aerosol scattering coefficients and aerosol number concentrations during the stagnation episode. Furthermore, the analysis of aerosol size distribution measurements has evidenced the large contribution of fine particles at ground level as well as in the atmospheric column during the stagnation period. The fine mode radius measured at Granada showed a large displacement towards larger sizes together with a pronounced increase in the geometric standard deviation of the fine mode during the high pollution event in the morning hours on 9 February. This was attributed to the growth of aerosol particles due to coagulation and condensation processes as a result of the high fine aerosol load next to the surface favoured by the high pressure system and thermal inversion on that day. This increases in the radius and width of the fine mode results in more efficient scattering in the 440–1020 nm spectral range which, in combination with nearly constant and low imaginary refractive index (0.002) leads to high single scattering albedo with neutral spectral dependency. During the persistent temperature inversion episode the daily European PM10 mass concentration limit (50 μg m−3) was exceeded in Granada for most days and in Málaga for three consecutive days. Nevertheless, the mass concentrations of NO2, CO and O3 were below the European thresholds with a noticeable decrease in O3 mass concentration at both sites.

Spatial variation of aerosol optical properties around the high-alpine site Jungfraujoch (3580 m a.s.l.)

Abstract. This paper presents results of the extensive field campaign CLACE 2010 (Cloud and Aerosol Characterization Experiment) performed in summer 2010 at the Jungfraujoch (JFJ) and the Kleine Scheidegg (KLS) in the Swiss Alps. The main goal of this campaign was to investigate the vertical variability of aerosol optical properties around the JFJ and to show the consistency of the different employed measurement techniques considering explicitly the effects of relative humidity (RH) on the aerosol light scattering. Various aerosol optical and microphysical parameters were recorded using in-situ and remote sensing techniques. In-situ measurements of aerosol size distribution, light scattering, light absorption and scattering enhancement due to water uptake were performed at the JFJ at 3580 m a.s.l.. A unique set-up allowed remote sensing measurements of aerosol columnar and vertical properties from the KLS located about 1500 m below and within the line of sight to the JFJ (horizontal distance of approx. 4.5 km). In addition, two satellite retrievals from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) and the Moderate Resolution Imaging Spectroradiometer (MODIS) as well as back trajectory analyses were added to the comparison to account for a wider geographical context. All in-situ and remote sensing measurements were in clear correspondence. The ambient extinction coefficient measured in situ at the JFJ agreed well with the KLS-based LIDAR (Light Detection and Ranging) retrieval at the altitude-level of the JFJ under plausible assumptions on the LIDAR ratio. However, we can show that the quality of this comparison is affected by orographic effects due to the exposed location of the JFJ on a saddle between two mountains and next to a large glacier. The local RH around the JFJ was often higher than in the optical path of the LIDAR measurement, especially when the wind originated from the south via the glacier, leading to orographic clouds which remained lower than the LIDAR beam. Furthermore, the dominance of long-range transported Saharan dust was observed in all measurements for several days, however only for a shorter time period in the in-situ measurements due to the vertical structure of the dust plume. The optical properties of the aerosol column retrieved from SEVIRI and MODIS showed the same magnitude and a similar temporal evolution as the measurements at the KLS and the JFJ. Remaining differences are attributed to the complex terrain and simplifications in the aerosol retrieval scheme in general.

Aerosol chemical composition at Cabauw, The Netherlands as observed in two intensive periods in May 2008 and March 2009

Abstract. Observations of aerosol chemical composition in Cabauw, the Netherlands, are presented for two intensive measurement periods in May 2008 and March 2009. Sub-micron aerosol chemical composition was measured by an Aerodyne Aerosol Mass Spectrometer (AMS) and is compared to observations from aerosol size distribution measurements as well as composition measurements with a Monitor for AeRosol and GAses (MARGA) based instrument and a Thermal-Desorption Proton-Transfer-Reaction Mass-Spectrometer (TD-PTR-MS). An overview of the data is presented and the data quality is discussed. In May 2008 enhanced pollution was observed with organics contributing 40% to the PM1 mass. In contrast the observed average mass loading was lower in March 2009 and a dominance of ammonium nitrate (42%) was observed. The semi-volatile nature of ammonium nitrate is evident in the diurnal cycles with maximum concentrations observed in the morning hours in May 2008 and little diurnal variation observed in March 2009. Size dependent composition data from AMS measurements are presented and show a dominance of organics in the size range below 200 nm. A higher O:C ratio of the organics is observed for May 2008 than for March 2009. Together with the time series of individual tracer ions this shows the dominance of OOA over HOA in May 2008.

Measurement of the atmospheric aerosol particle size distribution in a highly polluted mega-city in Southeast Asia (Dhaka-Bangladesh)

Aerosol particle size distribution was measured with an aerodynamic particle sizer (APS) spectrometer continuously from January 21 to April 24, 2006 in Dhaka, Bangladesh. Particles number, surface and mass distributions data were stored automatically with Aerosol Instrument Manager (AIM) software on average every half an hour in a computer attached to the APS. The grand total average of number, surface and mass concentrations were 8.2 × 103 ± 7.8 × 103 particles cm−3, 13.3 × 103 ± 11.8 × 103 μm2 cm−3 and 3.04 ± 2.10 mg m−3, respectively. Fine particles with diameter smaller than 1.0 μm aerodynamic diameter (AD) dominated the number concentration, accounted for 91.7% of the total particles indicating vehicular emissions were dominating in Dhaka air either from fossil fuel burning or compressed natural gas (CNGs). The surface and mass concentrations between 0.5 and 1.0 μm AD were about 56.0% and 26.4% of the total particles, respectively. Remarkable seasonal differences were observed between winter and pre-monsoon seasons with the highest monthly average in January and the lowest in April. Aerosol particles in winter were 3.79 times higher for number, 3.15 times for surface and 2.18 times for mass distributions than during the pre-monsoon season. Weekends had lower concentrations than weekdays due to less vehicular traffic in the streets. Aerosol particles concentrations were about 15.0% (ranging from 9.4% to 17.3%) higher during traffic peak hours (6:00am–8:00pm) than off hours (8:00pm–6:00am). These are the first aerosol size distribution measurements with respect to number, surface and mass concentrations in real time at Dhaka, Bangladesh.

Aerosol size distribution from inversion of solar radiances and measured at ground-level during SPALI10 campaign

A comparison of columnar versus ground-level measurements of aerosol size distribution is presented. The purpose was to understand what atmospheric conditions are most suitable for closure between: 1) ground-based remote sensing instruments measuring vertical column-integrated optical and microphysical properties and 2) ground-based in-situ aerosol instruments measuring microphysical properties at the surface scaled to height using aerosol backscatter profiles from lidar measurements. Measurements were taken during the SPALI10 (SPAin Lidar Intercomparison 2010) field campaign at Madrid from 18 October to 5 November 2010 within the frame of the EARLINET-ASOS project. Monitoring included aerosol measurements of size distribution as well as chemical composition. Both combined Scanning Mobility Particle Sizer and Optical Particle Counters were used for determining aerosol size distribution ranging from 15nm to 10μm. Additionally, the column-integrated characterization of the atmospheric aerosol was provided by a sun tracking photometer using a methodology based on non-spherical particles. Two different synoptic situations were analyzed: a stagnation scenario with growing pollution concentrations and a clean atmosphere with low aerosol particle load. The shape of the ground-level aerosol size distribution matches with the column-integrated in both scenarios but absolute values disagree, particularly with stagnation. Better agreement was found for clean atmospheric situations when the mixing layer reaches higher altitudes and the aerosol concentration within the atmosphere follows an exponential decay profile with height.

Unipolar charging based, hand-held mobility spectrometer for aerosol size distribution measurement

A hand-held particle size spectrometer for monitoring workplace exposure to aerosols and nanoparticles with 13 channels in the 15–630nm has been described. The instrument uses electrical mobility-based size classification in which aerosol particles are electrically charged using a unipolar corona charger, followed by classification in a condenser-type disk classifier, and particle counting using a commercial handheld condensation particle counter (CPC; Model 3007, TSI Inc., Shoreview, MN). A unipolar charger was designed to reduce multiple charging of particles which helped extend the measurable size range. The electrical classifier, which served as a low-pass mobility filter, was operated at 2:1 sheath-to-aerosol flow ratio using a single pump inside the CPC. An inversion scheme was developed to obtain discrete size distributions from cumulative mobility distributions. The sizing accuracy was also experimentally investigated using DMA-classified, near-monodisperse particles and was found to be in the range 1.4–8.1% below 300nm, and increased to 13.6% for 500nm particle. Experimentally measured sizing uncertainties ranged from 78–114%. The counting uncertainties of the instrument were in the range 0.1–10.5% for typical concentration range for ambient and workplace aerosols. Size distributions of test unimodal and bimodal polydisperse aerosols measured using HPSS agreed reasonably well with that from the laboratory scanning mobility spectrometer. HPSS can be useful in many routine monitoring applications, though the measured uncertainties can be large for some applications.

Modification of Laminar Flow Ultrafine Condensation Particle Counters for the Enhanced Detection of 1 nm Condensation Nuclei

This paper describes simple modifications to thermally diffusive laminar flow ultrafine condensation particle counters (UCPCs) that allow detection of ∼1 nm condensation nuclei with much higher efficiencies than have been previously reported. These non-destructive modifications were applied to a commercial butanol-based UCPC (TSI 3025A) and to a diethylene glycol-based UCPC (UMN DEG-UCPC). Size and charge dependent detection efficiencies using the modified UCPCs (BNL 3025A and BNL DEG-UCPC) were measured with high resolution mobility classified aerosols composed of NaCl, W, molecular ion standards of tetra-alkyl ammonium bromide, and neutralizer-generated ions. With negatively charged NaCl aerosol, the BNL 3025A and BNL DEG-UCPC achieved detection efficiencies of 37% (90× increase over TSI 3025A) at 1.68 nm mobility diameter (1.39 nm geometric diameter) and 23% (8× increase over UMN DEG-UCPC) at 1.19 nm mobility diameter (0.89 nm geometric diameter), respectively. Operating conditions for both UCPCs were identified that allowed negatively charged NaCl and W particles, but not negative ions of exactly the same mobility size, to be efficiently detected. This serendipitous material dependence, which is not fundamentally understood, suggests that vapor condensation might sometimes allow for the discrimination between air “ions” and charged “particles.” As a detector in a scanning mobility particle spectrometer (SMPS), a UCPC with this strong material dependence would allow for more accurate measurements of sub-2 nm aerosol size distributions due to the reduced interference from neutralizer-generated ions and atmospheric ions, and provide increased sensitivity for the determination of nucleation rates and initial particle growth rates. Copyright 2012 American Association for Aerosol Research

The climate penalty for clean fossil fuel combustion

Abstract. To cope with the world's growing demand for energy, a large number of coal-fired power plants are currently in operation or under construction. To prevent environmental damage from acidic sulphur and particulate emissions, many such installations are equipped with flue gas cleaning technology that reduces the emitted amounts of sulphur dioxide (SO2) and nitrogen dioxide (NO2). However, the consequences of this technology for aerosol emissions, and in particular the regional scale impact on cloud microphysics, have not been studied until now. We performed airborne investigations to measure aerosol size distributions in the air masses downwind of coal-fired power installations. We show how the current generation of clean technology reduces the emission of sulphur and fine particulate matter, but leads to an unanticipated increase in the direct emission of ultrafine particles (1–10 nm median diameter) which are highly effective precursors of cloud condensation nuclei (CCN). Our analysis shows how these additional ultrafine particles probably modify cloud microphysics, as well as precipitation intensity and distribution on a regional scale downwind of emission sources. Effectively, the number of small water droplets might be increased, thus reducing the water available for large droplets and rain formation. The possible corresponding changes in the precipitation budget with a shift from more frequent steady rain to occasionally more vigorous rain events, or even a significant regional reduction of annual precipitation, introduce an unanticipated risk for regional climate and agricultural production, especially in semi-arid climate zones.

Size-resolved aerosol water uptake and cloud condensation nuclei measurements as measured above a Southeast Asian rainforest during OP3

Abstract. The influence of the properties of fine particles on the formation of clouds and precipitation in the tropical atmosphere is of primary importance to their impacts on radiative forcing and the hydrological cycle. Measurements of aerosol number size distribution, hygroscopicity in both sub- and supersaturated regimes and composition were taken between March and July 2008 in the tropical rainforest in Borneo, Malaysia, marking the first study of this type in an Asian tropical rainforest. Hygroscopic growth factors (GF) at 90 % relative humidity (RH) for the dry diameter range D0 = 32–258 nm, supersaturated water uptake behaviour for the dry diameter range D0 = 45–300 nm and aerosol chemical composition were simultaneously measured using a Hygroscopicity Tandem Differential Mobility Analyser (HTDMA), a Droplet Measurement Technologies Cloud Condensation Nuclei counter (CCNc) and an Aerodyne Aerosol Mass Spectrometer (AMS) respectively. The hygroscopicity parameter κ was derived from both CCNc and HTDMA measurements, with the resulting values of κ ranging from 0.05–0.37, and 0.17–0.37, respectively. Although the total range of κ values is in good agreement, there are inconsistencies between CCNc and HTDMA derived κ values at different dry diameters. Results from a study with similar methodology performed in the Amazon rainforest report values for κ within a similar range to those reported in this work, indicating that the aerosol as measured from both sites shows similar hygroscopic properties. However, the derived number of cloud condensation nuclei (NCCN) were much higher in the present experiment than the Amazon, resulting in part from the increased total particle number concentrations observed in the Bornean rainforest. This contrast between the two environments may be of substantial importance in describing the impacts of particles in the tropical atmosphere.

Measurements of Aerosol Charge and Size Distribution for Graphite, Gold, Palladium, and Silver Nanoparticles

The role of charge on aerosol evolution and hence the nuclear source term has been an issue of interest, and there is a need for both experimental techniques and modeling for quantifying this role. Our focus here is on further exploration of a tandem differential mobility analyzer (TDMA) technique to simultaneously measure both the size and charge (positive, negative, and neutral) dependent aerosol distributions. We have generated graphite, gold, silver, and palladium nanoparticles (aerosol) using a spark generator. We measure the electrical mobility-size distributions for these aerosols using a TDMA, and from these data we deduce the full charge-size distributions. We observe asymmetry in the particle size distributions for negative and positive charges. This asymmetry could have a bearing on the dynamics of charged aerosols, indicating that the assumption of symmetry for size distributions of negatively and positively charged particles in source term simulations may not always be appropriate. Also, the experimental technique should find applications in measurements of aerosol rate processes that are affected by both particle charge and size (e.g., coagulation, deposition, and resuspension), and hence in modeling and simulation of the nuclear source term.

Comprehensive Measurement of Atmospheric Aerosols with a Wide Range Aerosol Spectrometer

A wide range aerosol spectrometer (WRAS) was used for comprehensive long term measurements of aerosol size distributions. The system combines the results of an optical aerosol spectrometer with the results of a Scanning Mobility Particle Sizer (SMPS) to record essentially the full size range (5 nm – 32 μm) of atmospheric particles in 72 channels. Measurements were carried out over one year (2009) at the Global Atmospheric Watch (GAW)-Station Hohenpeißenberg, Bavaria. Total particle number concentrations obtained from the aerosol size distributions were compared to the total number concentrations measured by a Condensation Particle Counter (CPC). The comparison showed an excellent agreement of the data. The high time resolution of 5 minutes allows the combination of the measured size distributions with meteorological data and correlations to gaseous pollutants (CO, NOx and SO2). A good correlation of particle number and CO concentrations was found for long distance transported small particles, which were probably mainly soot particles. Correlations to NOx were observed for aerosols from local sources such as traffic emissions. The formation of secondary aerosols from gaseous precursors was also observed. Episodes of relatively high concentration of particles in the range of 2-3 μm were probably caused by pollen.