On the sensitivity of particle size to relative humidity for Los Angeles aerosols

A TDMA system (Tandem Differential Mobility Analyzer; Rader D.J. and McMurry P.H. J. Aerosol Sci. 17, 771–787, 1986) was used to measure the sensitivity of particle size to relative humidity for monodisperse Los Angeles aerosols. Measurements were made at Claremont, CA on 13 days between 19 June and 3 September 1987, in conjunction with the Southern California Air Quality Study (SCAQS). The particle sizes that were studied ranged from 0.05 μm to 0.5 μm diameter at ambient relative humidity (typically 45–65%).The data provide clear evidence that these atmospheric aerosols were externally mixed. Monodisperse ambient aerosols were often found to split into nonhygroscopic (no water uptake) and hygroscopic portions when humidified. An average of 30% of the particles in the 0.2–0.5 μm range were nonhygroscopic. However, the proportion of the particles that was nonhygroscopic varied considerably from day to day and was, on occasion, as high as 70–80% of the particles. There was no clear evidence for nonhygroscopic 0.05 μm particles, but the data are not definitive on this point.The data also show that for the hydrophilic aerosol fraction, the larger particles (0.4–0.5 μm) grew more when humidified than did smaller particles (0.05–0.2 μm). As relative humidities were increased from 50% to 90%, particle diameters grew by average factors of 1.46 ±0.02 (for 0.5 μm particles), 1.49 ± 0.08 (0.4 μm), 1.19 ± 0.08 (0.2 μm) and 1.12 ± 0.05 (0.05 μm). Similarly, when particles were dried from 50% RH to 6–10% RH, particle diameters changed by factors ranging from 0.94 ± 0.03 (0.5 μm) to 0.98 ± 0.01 (0.05 μm).     

Trace elements and sea salt aerosols over the sea areas around the Indian sub-continent

The nature and the characteristics of trace elements and sea salt aerosols in the ocean atmosphere around the Indian sub-continent was studied. For this purpose, concentrations of the total suspended particulates (TSP) as well as of its various chemical components together with their mass size distributions were measured on 11 days in May 1983. Over the sea regions around the sub-continent, sampling was done on board the research Vessel Gaveshani using a high volume air sampler and a multistage Andersen sampler. The concentrations of soil-origin elements (Al, Fe, Mn and Ca) were found to be at a maximum over the Arabian sea region suggesting the presence of dust particulates, transported from the Arabian peninsula. The near sea water ratio of CI/ Na was observed in giant size (> 2.5 μm dia) sea salt aerosols suggested that there was very little fractionation in these aerosols. The ratio value considerably decreased in the case of sub-μm sea salt particles. The chemical components originating from soil and from sea salt showed a unimodal distribution whereas those from anthropogenic sources showed a bimodal distribution.     

Chemical characteristics of free tropospheric aerosols over the Japan Sea coast: aircraft-borne measurements

Atmospheric aerosol particulate matter was directly collected in the free troposphere over the Japan Sea coast between 1992 and 1994 using an aircraft-borne nine-stage cascade impactor (particle size range: 0.1–8 μm). The water-soluble components in the aerosol particulate matter were analyzed by ion chromatography. Particulate sulfate and ammonium were detected in most of the samples and their size distributions showed noticeable peaks below the 1 μm particle size range. Water-soluble calcium (Ca²⁺) was detected in half of the samples; the size distribution showed that the maximum particle size was larger than 1 μm. Highly concentrated Ca²⁺ in larger particles was possibly due to transport of Kosa aerosols from the Asian continent in the free troposphere. The concentration of fine particulate sulfate and ammonium tended to increase whenever Ca²⁺ was detected, which suggests possible mixing of Kosa aerosols and non-Kosa aerosols during long-range transport of air masses containing Kosa particles.     

Size distribution of atmospheric aerosols in seoul

Urban aerosol particle size distributions over the size range 0.01–1.0 μm have been determined by using an electrical aerosol analyzer at the Hanyang University in Seoul from May through to October 1984. The results indicate that the total average number distribution in the size range of 0.1–1.0 μm can be represented as the Junge distribution with dN/d(logD_p) = 28.9 D_p^−3.1. The total average surface distribution is characterized by a monomodal curve with its maximum in the vicinity of 0.13 μm, while the maximum of the total average volume distribution appears to be shifted to a larger size than that of the surface distribution showing an almost flat line for D_p 0.5 μm, which implies that a secondary maximum may exist for D_p 1.0 μm.The time development of the number size distributions for the total size range shows the minimum number in the early morning before 4 a.m. followed by a rapid increase by the morning rush hour. This development in the 0.1–1.0 μm range is characterized by the maximum numbers in the morning and evening rush hours when dense traffic and a low mixing depth coexist with high relative humidity. The photochemical production of small particles in the 0.01–0.1 μm range is verified from monthly variation of number concentration and duration of sunshine.In general the monthly development of the surface and volume distributions shows the highest values to be in spring with the lowest in summer.     

Measurement of the 210Po/210Pb activity ratio in size fractionated aerosols from the coast of the Japan sea

The seasonal variation of the ²¹⁰Po/²¹⁰Pb activity ratio in aerosols, as a function of particle size, have been studied at Kamo, on the west coast of Japan from July 1995 to June 1996. It was shown that 70% of ²¹⁰Po and 77% of ²¹⁰Pb activities were measured in aerosols with a diameter smaller than 0.7 μm. On the other hand, the abundances of ²¹⁰Po and ²¹⁰Pb in aerosols with a diameter larger than 10.9 μm were 3 and 1%, respectively. In general, the maxima of the ²¹⁰Po/²¹⁰Pb ratio were observed in aerosols of 5.4–10.9 μm, but the maxima in January and April 1996 appeared in the largest and the smallest size fractions, respectively. The results suggest that the size distribution of the ²¹⁰Po/²¹⁰Pb activity ratio may be modified by changes in the nature and intensity of aerosol sources.     

Aerosol optical and physical properties during winter monsoon pollution transport in an urban environment

We analysed aerosol optical and physical properties in an urban environment (Kolkata) during winter monsoon pollution transport from nearby and far-off regions. Prevailing meteorological conditions, viz. low temperature and wind speed, and a strong downdraft of air mass, indicated weak dispersion and inhibition of vertical mixing of aerosols. Spectral features of WinMon aerosol optical depth (AOD) showed larger variability (0.68–1.13) in monthly mean AOD at short-wavelength (SW) channels (0.34–0.5 μm) compared to that (0.28–0.37) at long-wavelength (LW) channels (0.87–1.02 μm), thereby indicating sensitivity of WinMon AOD to fine aerosol constituents and the predominant contribution from fine aerosol constituents to WinMon AOD. WinMon AOD at 0.5 μm (AOD _{0. 5}) and Angstrom parameter ( α) were 0.68–0.82 and 1.14–1.32, respectively, with their highest value in December. Consistent with inference from spectral features of AOD, surface aerosol loading was primarily constituted of fine aerosols (size 0.23–3 μm) which was 60–70 % of aerosol 10- μm (size 0.23–10 μm) concentration. Three distinct modes of aerosol distribution were obtained, with the highest WinMon concentration at a mass median diameter (MMD) of 0.3 μm during December, thereby indicating characteristics of primary contribution related to anthropogenic pollutants that were inferred to be mostly due to contribution from air mass originating in nearby region having predominant emissions from biofuel and fossil fuel combustion. A relatively higher contribution from aerosols in the upper atmospheric layers than at the surface to WinMon AOD was inferred during February compared to other months and was attributed to predominant contribution from open burning emissions arising from nearby and far-off regions. A comparison of ground-based measurements with Moderate Resolution Imaging Spectroradiometer (MODIS) data showed an underestimation of MODIS AOD and α values for most of the days. Discrepancy in relative distribution of fine and coarse mode of MODIS AOD was also inferred.     

Aliphatic and aromatic hydrocarbons in different sized aerosols over the Mediterranean Sea: Occurrence and origin

Marine aerosols were collected using a five-stage cascade impactor during the PHYCEMED II cruise in the Western Mediterranean Sea (October 1983). Their composition in aliphatic and aromatic hydrocarbons (HCs) was analyzed, representing the first time that concentrations of polynuclear aromatic HCs (PAH) are reported in relation to particle size for aerosols of remote marine areas. The HC concentrations were found to be dependent on the origin of the air masses. They were higher for air coming from North European countries than for air originating in the Atlantic and the South of Spain. The concentrations range between 7 and 14 ng m⁻³for n-alkanes and between 0.2 and 0.4 ng m⁻³for total PAH. Based on molecular criteria, several sources for these HCs have been identified: continental higher plant waxes, petroleum and pyrolysis (namely coal combustion and vehicular exhausts). Mass medium equivalent diameters (MMED) for the naturally derived n-alkanes are in the 1.79-2.53 μm range, indicating an origin related with the emission of large particles from higher plant waxes or from soil dusts. In contrast, MMED for the anthropogenic HCs, both aliphatic and aromatic, are smaller than the micron, suggesting initial emission of PAH through pyrolytic processes in the vapor phase followed by condensation onto larger sub-μm particles.     

Distribution of polybrominated diphenyl ethers and dust particle size fractions adherent to skin in indoor dust,Pretoria, South Africa

In order to determine human exposure to the indoor toxicant, selection of dust fraction and understanding dust particle size distribution in settled indoor dust are very important. This study examined the influence of dust particle size on the concentration of polybrominated diphenyl ethers (PBDEs) congeners, assessed the distribution of dust particle size and characterized the main indoor emission sources of PBDEs. Accordingly, the concentrations of PBDE congeners determined in different indoor dust fractions were found to be relatively higher in the order of dust particle size: 45–106 μm?>?(<45 μm)?>?106–150 μm. The finding shows arbitrary selection of dust fractions for exposure determination may result in wrong conclusions. Statistically significant moderate correlation between the concentration of Σ₉PBDEs and organic matter content calculated with respect to the total dust mass was also observed (r?=?0.55, p?=?0.001). On average, of total dust particle size <250 μm, 93.4 % (m/m%) of dust fractions was associated with less than 150 μm. Furthermore, of skin adherent dust fractions considered (<150 μm), 86 % (v/v%) is in the range of particle size 9.25–104.7 μm. Electronic materials treated with PBDEs were found the main emission sources of PBDE congeners in indoor environment. Based on concentrations of PBDEs determined and mass of indoor dust observed, 150 μm metallic sieve is adequate for human exposure risk assessment. However, research in this area is very limited and more research is required to generalize the fact.     

Size distributions of airborne microbes in moisture-damaged and reference school buildings of two construction types

Any risk assessment of moisture-damaged buildings requires an accurate characterization of the factors contributing to the human exposure. In this study, the size distributions of indoor air viable fungi and bacteria and average mean diameters of the most common fungi in school buildings were determined. One special focus was to analyze how the microbial size distributions are affected by the building frame (either wooden or concrete) and moisture damage in the building. The study was performed in 32 school buildings classified as moisture-damaged (index) and non-damaged (reference) schools according to technical building investigations. Sampling for indoor air microbes was carried out using a cascade impactor that collects particles on six stages (range from 0.65 to >7 μm) according to their aerodynamic diameters. Both wooden and concrete schools had their highest fungal levels in the size range of 1.1–4.7 μm. However, the concentrations of fungi in all size classes were higher in wooden schools than in concrete schools. Moisture damage-associated differences in size distribution, in the particle size range of 1.1–2.1 μm, were seen in concrete schools but not in wooden schools. In general, the average geometric mean diameter (d_g,ave) of total viable fungi was smaller in wooden schools than in concrete schools, and smaller in index schools of both construction types than in their reference schools. Variation in particle size, however, by genus was observed. No differences in particle size distributions of viable airborne bacteria were found. Our results on the dependency of the particle size on the building type and presence of moisture damage provide an interesting point to be considered in assessing the complex issue of indoor-related bioaerosol exposures.     

Distribution characteristics of polycyclic aromatic hydrocarbons with particle size in urban aerosols at the roadside in Ho Chi Minh City,Vietnam

The purpose of this study was to characterize size distributions of atmospheric polycyclic aromatic hydrocarbons (PAHs) with 4–6 rings at the roadside in Ho Chi Minh City, Vietnam. Ten PAHs (fluoranthene, pyrene, triphenylene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[ghi]perylene and indeno[1,2,3-cd]pyrene) in atmospheric particulate matters (PM) at the roadside were measured in the dry and rainy seasons in 2005 at Ho Chi Minh City, using a low-pressure cascade impactor. The PM were separated into nine fractions by their aerodynamic diameter, i.e. >9.0, 9.0–5.8, 5.8–4.7, 4.7–3.3, 3.3–2.1, 2.1–1.1, 1.1–0.7, 0.7–0.4 and <0.4 μm (a final filter). PAHs were analyzed by high-performance liquid chromatography with fluorescence detection. Total PAHs measured were higher in the rainy season than in the dry season. The mass of coarse particles occupied a higher fraction than that of fine particles in both seasons. Total PAHs were mainly concentrated in particles with aerodynamic diameter smaller than 0.4 μm. The particle size distributions of PAHs investigated were bi-modal with a peak in fine particle mode (<2.1 μm) and another peak in coarse particle mode (>2.1 μm). Generally, 5,6-ring PAHs associated mainly with fine particles and 4-ring PAHs spread out in both fine and coarse particles.     

The physical characteristics of sulfur aerosols

A review of the physical characteristics of sulfur-containing aerosols, with respect to size distribution of the physical distributions, sulfur distributions, distribution modal characteristics, nuclei formation rates, aerosol growth characteristics, and in situ measurement, has been made.Physical size distributions can be characterized well by a trimodal model consisting of three additive lognormal distributions.When atmospheric physical aerosol size distributions are characterized by the trimodal model, the following typical modal parameters are observed:1. Nuclei mode – geometric mean size by volume, DGV_n, from 0.015 to 0.04 μm. σ_gn=1.6, nucler mode volumes from 0.0005 over the remote oceans to 9 μm³ cm⁻³ on an urban freeway.2. Accumulation mode – geometric mean size by volume, DGV_a, from 0.15 to 0.5 μm, σ_ga=1.6–2.2 and mode volume concentrations from 1 for very clean marine or continental backgrounds to as high as 300 μm³ cm⁻³ under very polluted conditions in urban areas.3. Coarse particle mode – geometric mean size by volume, DGV_c, from 5 to 30 μm, σ_gn=2–3, and mode volume concentrations from 2 to 1000 μm³ cm⁻³.It has also been concluded that the fine particles (D_p<2 μm) are essentially independent in formation, transformation and removal from the coarse particles (D_p>2 μm).Modal characterization of impactor-measured sulfate size distributions from the literature shows that the sulfate is nearly all in the accumulation mode and has the same size distribution as the physical accumulation mode distribution.Average sulfate aerodynamic geometric mean dia. was found to be 0.48±0.1 μm (0.37±0.1 μm vol. dia.) and σ_g=2.00±0.29. Concentrations range from a low of about 0.04 μg m⁻³ over the remote oceans to over 8 μg m⁻³ under polluted conditions over the continents.Review of the data on nucleation in smog chambers and in the atmosphere suggests that when SO₂, is present, SO₂-to-aerosol conversion dominates the Aitken nuclei count and, indirectly, through coagulation and condensation, the accumulation mode size and concentration. There are indications that nucleation is ubiquitous in the atmosphere, ranging from values as low as 2 cm⁻³ h⁻¹ over the clean remote oceans to a high of 6×10⁶ cm⁻³ h⁻¹ in a power plant plume under sunny conditions.There is considerable theoretical and experimental evidence that even if most of the mass for the condensational growth of the accumulation mode comes from hydrocarbon conversion, sulfur conversion provides most of the nuclei.     

The Mass Distribution of Large Atmospheric Particles

This paper describes the results of a study to determine the total mass and the mass distribution of atmospheric aerosols, especially that mass associated with particles greater than 10 μm diameter. This study also determined what fraction of the total aerosol mass a standard high-volume air sampler collects and what fraction and size interval settle out on a dust fall plate. A special aerosol sampling system was designed for this study to obtain representative samples of large airborne particles. A suburban sampling site was selected because no local point sources of aerosols existed nearby. Samples were collected under various conditions of wind velocity and direction to obtain measurements on different types of aerosols.

Study measurements show that atmospheric particulate matter has a bimodal mass distribution. Mass associated with large particles mainly ranged from 5 to 100 μm in size, while mass associated with small particles ranged from an estimated 0.03 to 5 μm in size. Combined, these two distributions produced a bimodal mass distribution with a minimum around 5 μm diameter. The high-volume air sampler was found to collect most of the total aerosol mass, not just that fraction normally considered suspended particulate. Dust fall plates did not provide a good or very useful measure of total aerosol mass. The two fundamental processes of aerosol formation, condensation and dispersion appear to account for the formation of a bimodal mass distribution in both natural and anthropogenic aerosols. Particle size distribution measurements frequently are in error because representative samples of large airborne particles are not obtained. Considering this descrepancy, air pollution regulations should specify or be based upon an upper particle size limit.     

The modality of particle size distributions of environmental aerosols

Knowledge of the distribution of airborne particulate matter into size fractions has become an increasing area of focus when examining the effects of air pollution. While total number and mass concentrations may play an important role in exposure and risk assessment analyses, often an understanding of the particle size distributions provides more information on the type of atmospheric processes resulting in the distributions. The modality of the particle size distribution is one such aspect that has been associated with the aerosol formation mechanisms. The aim of this work is to provide a detailed analysis of the modal characteristics of a large number of particle size spectra collected over a period of three years for a range of ambient aerosol types. Measurements of over 6000 size distributions in the size range 0.016–30 μm were made using a scanning mobility particle sizer and an aerodynamic particle sizer for various ambient aerosols including: traffic influenced, urban, vegetation burning influenced, marine, modified background and suburban. Advanced data analytical procedures were adopted to combine the distributions from the two instruments for the calculation of the volume size distributions to allow clear interpretation of the modal characteristics. It was determined that, while in most cases there is a distinct nuclei mode in the number size distribution, this does not translate to a nuclei mode in the volume size distribution. Furthermore, while many of the number size distributions were different for each aerosol studied, the volume distributions were similar. This finding has serious implications for the setting of mass-based air quality standards.     

Size distribution of large aerosol particles during AGASP-II: Absence of st. augustine eruptive particles in the Alaskan Arctic

Number distribution data for 0.1–45 μm diameter aerosol were obtained using optical counting and sizing probes flown over the Alaskan Arctic during the second Arctic Gas and Aerosol Sampling Program (AGASP-II), flights 201–203. Due to noise present in the lowest size channels of the optical probes, estimates of the H₂SO₄ component of Arctic haze were not attempted. Large particle (> 0.5 μm diameter) results are presented here. Large particle number and volume concentration were determined along with estimated mass, which was generally </ 0.1μg m⁻³. Lognormal fitting to > 0.3 μg m⁻³ mass loading sizedistributed aerosol data produced a means for comparing volume geometric median diameters (VGMD) for these higher-mass time intervals. These VGMDs showed that solid crustal particles previously observed during AGASP-II had VGMDs in the 1.2–1.6 μm range and that the shape of these fitted lognormal distributions was essentially constant. This result suggests very-long-range transport from a distant crustal source and, in conjunction with aerosol physical and chemical characterization data, argues against the presence of the Mt. Augustine eruptive particles during AGASP-II Alaskan Arctic sampling.     

Middle and lower troposphere aerosol characteristics and ozone concentrations over northwestern Greece during STAAARTE 1997

Accumulation aerosol particle distributions were measured on 14 June 1997 during two research flights over northwestern Greece, including the greater Thessaloniki area (GTA). At flight altitudes of about 5000 m (<550 mb), accumulation mode number particle size distributions appeared to be unimodal with a maximum in the first bin of the measured number size distribution with a mid-point of 0.11 μm. At lower altitudes and over the GTA, accumulation mode particle size distributions were bimodal with a first mode peak at 0.125 μm and a second mode peak at 0.275 μm. The second mode was more pronounced in areas of higher relative humidity, thus indicating the presence of deliquescent aerosols, but also in areas where high O₃ concentrations were measured. Ozone concentrations ranged between 25 and 60 ppb at high altitudes east of GTA and between 50 and 110 ppb over the city of Thessaloniki with the maximum measured at an altitude of about 500 m. This is consistent with the local topographical and meteorological conditions, mainly due to the nocturnal inversion and the development of local circulation flows (land and sea breeze) over the city.     

Influence of air mass source region on nanoparticle events and hygroscopicity in central Virginia,U.S.

During autumn, 2006, variation in the frequency of aerosol nucleation events, as inferred from nanoparticle growth events, and associated hygroscopicity were investigated as a function of air mass transport history at a mixed deciduous forest in central Virginia, U.S. Above-canopy size distributions of aerosols between 0.012 and 0.700 μm diameter, size-resolved particle hygroscopicity at eight dry diameters between 0.012 and 0.400 μm, and cloud condensation nuclei (CCN) activity were characterized. Air mass back trajectories were clustered to identify source regions. Growth events were most frequent in fast-moving air masses (mean = 9 m s^?1) that originated over the north central U.S. Under these flow regimes, mean values for preexisting sub-μm aerosol number concentrations (4700 cm^?3), corresponding surface area (142 μm² cm^?3), air temperature (6.2 °C), and relative humidity (RH, 49.4%) were relatively low compared to other regimes. Under stagnant flow conditions (mean = 3 m s^?1), mean number concentrations were higher (>6000 cm^?3) and size fractions <0.1 μm diameter exhibited enhanced hygroscopicity compared to other source regions. These results indicate that precursors emitted into relatively clean, cold, and dry air transported over the southeastern U.S. reacted to form condensable intermediates that subsequently produced new aerosols via nucleation and growth. This pathway was an important source for CCN. During events in October, nanoparticles were produced in greater numbers and grew more rapidly compared to November and December.     

Size-resolved trace metal characterization of aerosols emitted by four important source types in Switzerland

In central Switzerland five types of emission sources are mainly responsible for airborne trace metals: traffic, industrial plants burning heavy oil, resuspension of soil particles, residential heatings and refuse incineration plants. The particulate emissions of each of these source types except refuse incineration were sampled using Berner impactors and the mass and elemental size distributions of Cd, Cu, Mn, Pb, Zn, As and Na determined.Cd, Na and Zn are not characteristic for any of these source types. As and Cu, occurring in the fine particle fractions are characteristic for heavy oil combustion, Mn for soil dust and sometimes for heavy and fuel oil combustion and Pb for traffic aerosols. The mass size distributions of aerosols originating from erosion and abrasion processes show a maximum mass fraction in the coarse particle range larger than about 1 μm aerodynamic equivalent diameters (A.E.D.). Aerosols originating from combustion processes show a second maximum mass fraction in the fine particle range below about 0.5μm A.E.D.Scanning electron microscopy combined with an EDS analyzer was used for the morphological characterization of emission and ambient aerosols.     

Aerosol mass-size distributions at a tropical coastal environment: response to mesoscale and synoptic processes

Regular measurements of total mass concentration and mass-size distribution of near-surface aerosols, made using a ten-channel Quartz Crystal Microbalance (qcm) Impactor for the period October 1998–December 1999 at the tropical coastal station Trivandrum (8.5°N, 77°E), are used to study the response of aerosol characteristics to regional mesoscale and synoptic processes. Results reveal that aerosol mass concentrations are generally higher under land breeze conditions. The sea breeze generally has a cleansing effect, depleting the aerosol loading. The continental air (LB regime) is richer in accumulation mode (submicron) aerosols than the marine air. On a synoptic scale, aerosol mass concentration in the submicron mode decreased from an average high value of ∼86 μg m⁻³ during the dry months (January–March) to ∼11 μg m⁻³ during the monsoon season (June–September). On the contrary mass concentration in the supermicron mode increased from a low value of ∼15 μg m⁻³ during the dry months to reach a comparatively high value of ∼35 μg m⁻³ during April, May. Correspondingly, the effective radius (R_eff) increased from a low value of 0.15–0.17 μm to ∼0.3 μm indicating a seasonal change in the size distribution. The mass-size distribution shows mainly three modes, a fine mode (∼0.1 μm); a large mode (∼0.5 μm) and a coarse mode (∼3 μm). The fine mode dominates in winter. In summer the large mode becomes more conspicuous and the coarse mode builds up. The fine mode is highly reduced in monsoon and the large and coarse modes continue to remain high (replenished) so that their relative dominance increases. The size distribution tends to revert to the winter pattern in the post-monsoon season. Accumulation (submicron) aerosols account for ∼98% of the total surface area and ∼70% of the total volume of aerosols during winter. During monsoon, even though they still account for ∼90% of the area, their contribution to the volume is reduced to ∼50%; the coarse aerosols account for the rest.     

On the nature of nitrate particles in a coastal urban area

Application of micro spot and electron microscopy techniques to individual particles in a coastal urban site revealed the following:

• 1.(a) sulfate particles, some of them mixed, dominated the sub-μm (0.3–0.8 μm) size range;
• 2.(b) nitrates were found mostly in the μm size range, in the form of NaNO₃.

The latter was verified by X-ray analysis of individual nitrates. Apparently the NaNO₃ particles were formed through heterogeneous reaction of gaseous HNO₃ with sea salt particles.     

Atmospheric particle size distributions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) and their implications for wet and dry deposition

Concurrent measurements of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) in different size fractions of atmospheric particulate matter are presented for a winter and a summer sampling period. The PCDD/Fs and PAHs were primarily associated with particles of <1.35 μm aerodynamic diameter. The particle size distributions were similar for the compounds within each substance group and, surprisingly, also between the PCDD/Fs and PAHs. Changes in the particle size distribution of particle mass were reflected in the particle size distributions of the PCDD/Fs and PAHs.The data were employed to identify those particle size fractions dominating the wet and dry particle bound deposition of PCDD/Fs and PAHs and, furthermore, to assess the relative contributions of wet and dry deposition to the total particle bound deposition fluxes. The calculations indicate that coarse particles contribute most to the dry deposition while, in contrast, the wet deposition of the PCDD/Fs and PAHs is dominated by fine particles. Furthermore, it is estimated that in Bayreuth wet deposition dominates the total particle bound deposition of PCDD/Fs and PAHs.