Calibration of Sharp Cut Impactors for Indoor and Outdoor Particle Sampling

ABSTRACT

A low-flow rate, sharp cut point inertial impaction sampler was developed in 1986 that has been widely used in PM exposure studies in the United States and several other countries. Although sold commercially as the MS&T Area Sampler, this sampler is widely referred to as the Harvard Impactor, since the initial use was at the Harvard School of Public Health. Impactor nozzles for this sampler have been designed and characterized for flows of 4,10, 20, and 23 L/min and cut points of 1, 2, 5, and 10 |im. An improved method for determining the actual collecting efficiency curve was developed and used for the recent impactor calibrations reported here. It consists of placing a multiplet reduction impactor inline just downstream of the vibrating orifice aerosol generator to remove the multiplets, thus allowing only the singlet particle s to penetrate through to the impactor being calibrated.

This paper documents the techniques and results of recent nozzle calibrations for this sampler and compares it with other size-selective inertial impactors. In general, the impactors were found to have sharp cutoff characteristics. Particle interstage losses for all of the impactors were very low, with the exception of the 10-|im cut size 20 L/ min impactor, which had greater losses due to the higher flow rate. All of the cut nozzle laboratory calibrations compare favorably to the U.S. Environmental Protection Agency (EPA) WINS-96 fine particle mass (PM_{2 5}) impactor calibration data.     

A Transition-Flow Reactor Tube for Measuring Trace Gas Concentrations

Dry deposition contributes significantly to the acidification of ecosystems. However, difficulties in measuring dry deposition of reactive gases and fine particles make routine direct monitoring impractical. An alternate approach is to use the “concentration monitoring” method in which dry deposition flux is estimated as the product of measured concentration and estimated deposition velocity. A sampling system that performs over the period of 6 hours to 7 days, depending on atmospheric concentrations, has been developed. It consists of a Teflon cyclone to exclude particles larger than about 2 μm, selective solid adsorption media for reactive gases—some of which are sampled from a transition flow to avoid possible bias from particle evaporation, a particle filter, and a final gas adsorption filter to collect the remaining trace gas. The sampler Is the first reported application of transition flow mass transfer for the collection and quantitative measurement of trace atmospheric gases. Laboratory and field tests have shown that the sampler performs well for HNO₃(g).     

Combined effect of polystyrene plastics and triphenyltin chloride on the green algae Chlorella pyrenoidosa

The combined effect of polystyrene (PS) particles and triphenyltin chloride (TPTCl) to the green algae Chlorella pyrenoidosa was studied. The 96 h IC₅₀ of TPTCl to the green algae C. pyrenoidosa was 30.64 μg/L. The toxicity of PS particles to C. pyrenoidosa was size-dependent, with the 96 h IC₅₀ at 9.10 mg/L for 0.55 μm PS but no toxicity observed for 5.0 μm PS. The exposure to 0.55 μm PS led to damage on structure of algal cells, which could in turn cause inhibition on photosynthesis and population growth of the green algae. TPTCl concentrations in test medium were lowered by 15–19% at presence of 0.55 μm PS particles, indicating a reduced bioavailability of TPTCl. In spite of this reduced bioavailability, the presence of PS increased the toxicity of TPTCl, which might be attributed to facilitated uptake of TPTCl by the green algae after the damage of cell structure. The overall results of the present study provided important information on the effect of PS on the bioavailability and toxicity of TPTCl to phytoplankton species.

     

Predicting Cutoff Aerodynamic Diameter and Sharpness of Single Round-Nozzle Impactors with a Finite Impaction Plate Diameter

Abstract

This investigation numerically examined the cutoff aerodynamic diameter (da₅₀) and the sharpness (GSD) of the particle collection efficiency curve of impactors with a finite impaction plate diameter. Results revealed that the inertial impactors have a limited cutoff aerodynamic diameter at different air velocities. The extreme value of the cutoff aerodynamic diameter increases with the nozzle diameter (W)/the plate diameter (D_c). The computed da₅₀/D_c values of the impactors increase with W/D_c at various Reynolds numbers (Re) and with the nozzle-toplate distance (S)/D_c when Re is 100. The value of GSD slightly increases with W/D_c for Re of 10 and 100, although the effect of S/D_c on GSD is not evident at various Res. The particle collection efficiency curve of the impactor with a lower Re is less sharp than that with a high Re at various W/D_c and S/D_c values. Statistical equations closely fitted the obtained numerical results for Res of 10–3000. The equations are useful for directly calculating the cutoff aerodynamic diameter and the sharpness of the particle collection efficiency curve for single round-nozzle impactors with a finite impaction D_c.     

Research on the effects of diesel engine exhaust transport distance on particulate microstructure

This study aims to reveal the evolutionary process of particles during the diesel exhaust transport process and to further understand the effects of diesel exhaust transport distance (D_ET) on a particulate microstructure. Specifically, the micromorphological, particle size distribution, and aggregate characteristics of particles as well as the variation of the structural characteristics of elementary carbon particles (ECPs) as D_ET changed were examined using an engine exhaust particle size spectrometer, a high-resolution transmission electron microscopy system, and a small-angle X-ray scattering system. The results show the following: As D_ET increased, the chains gradually lengthened, the extent of accumulation and stacking increased, and a number of clusters gradually rose. The average particle diameter increased from 23.1 nm at 0 m to 92.7 nm at 3 m. In addition, as D_ET increased, the number of accumulation-mode particles, the number of folded, curved carbon layers in the inner core of carbon particles, and the disorderliness of carbon layers in the outer shell of carbon particles all increased. Moreover, the boundary between the inner core and the outer shell became increasingly obscure. As D_ET increased, there was a gradual decrease in the difference in electron density between particles, and the fractal dimensionality of the distribution, average cross-sectional size, radius of gyration, and axial length of pores were, respectively, 33.3%, 40%, 38.2%, and 50.3% less at 3 m than at 0 m. Besides that, the number of small (< 3 nm) pores gradually increased, and the number of large (> 10 nm) pores gradually decreased. Overall, as D_ET increased, pore size and number decreased. There was a gradual increase in the number of folded and curved carbon layers in the inner core of ECPs and an increase in the disorderliness of carbon layers in their outer shell as D_ET increased. Furthermore, the boundary between the inner core and the outer shell became increasingly obscure as D_ET increased. The crystallite size of ECPs decreased from 1.365 nm at 0 m to 1.098 nm at 3 m. This suggests that the number of continuously arranged carbon atoms decreased, the arrangement of carbon atoms was more disorderly, and the degree of graphitization decreased. As D_ET increased, there was a gradual increase in the interlayer spacing and curvature of ECPs. This suggests that increasing D_ET led to a more disorderly distribution of electron orbitals inside the carbon layers, less electron resonance stability in the carbon layers, greater oxidative activity of ECPs, and greater inherent oxidative capacity of particles.

     

High-volume Impactor for Sampling Fine and Coarse Particles

Final design, calibration, and field testing have been completed for a new 1.13 m³/min (40 cfm) High-volume Virtual Impactor (HVVI). Field tests have demonstrated that the new classifier/collector works well as an accessory to the existing PM10 Size Selective Inlet high-volume samplers. The HVVI provides two fractions of PM10 mass, both of which are collected by filtration. The fine fraction (0-2.5 μm aero. dia.) Is collected on the standard 20.3 × 25.4 cm (8- × 10-in) high-volume filter; the coarse fraction (2.5-10 μm aero. dia.) is collected on a 5.1 × 15.2 cm (2- × 6-in) filter. Coarse flow through the receiver tubes is limited to 0.057 m³/min (2 cfm), 5 percent of the total flow.

The operating pressure drop across the HVVI stages Is sufficiently high to make changes In pressure across the collection filters Insignificant. The HVVI filter holder assembly facilitates loading/ unloading samples in the laboratory, thus eliminating damage due to handling filters in the field. Size separation characteristics of the HVVI agree well with those for the 16.7 L/min commercially available dichotomous sampler with the 50 percent effectiveness (cut-point) occurring at 2.5 μm. Applying laboratory-determined particle losses to the typical ambient particle mass size distribution described In Federal Register 49, 40 CFR, Part 53, Table D-3, the HVVI fine fraction total mass loss is less than 0.8 percent for liquid particles and less than 0.1 percent for solid particles; coarse fraction total mass loss is less than 2.5 percent for liquid particles, and less than 0.2 percent for solid particles.     

Controlled Exposures of Volunteers to Respirable Carbon and Sulf uric Acid Aerosols

Respirable carbon or fly ash particles are suspected to increase the respiratory toxicity of coexisting acidic air pollutants, by concentrating acid on their surfaces and so delivering it efficiently to the lower respiratory tract. To investigate this issue, we exposed 15 healthy and 15 asthmatic volunteers in a controlled- environment chamber (21°C, 50 percent relative humidity) to four test atmospheres: (i) clean air; (ii) 0.5-μm H2SO4 aerosol at =100 μg/m³, generated from water solution; (iii) 0,5-μm carbon aerosol at =250 μg/m³, generated from highly pure carbon black with specific surface area comparable to ambient pollution particles; and (iv) carbon as in (iii) plus =100 μg/m³ of ultrafine H2SO4 aerosol generated from fuming sulfuric acid. Electron microscopy showed that nearly all acid in (iv) became attached to carbon particle surfaces, and that most particles remained in the sub-μm size range. Exposures were performed double-blind, 1 week apart. They lasted 1 hr each, with alternate 10-min periods of heavy exercise (ventilation =50 L/min) and rest. Subjects gargled citrus juice before exposure to suppress airway ammonia. Lung function and symptoms were measured pre-exposure, after initial exercise, and at endexposure. Bronchial reactivity to methacholine was measured after exposure. Statistical analyses tested for effects of H₂SO₄ or carbon, separate or interactive, on health measures. Group data showed no more than small equivocal effects of any exposure on any health measure. One individual's responses were consistent with a clinically significant excess airway constriction from H₂SO₄ plus carbon, and 2-3 others showed slight excess responses to the combined pollutants, but all these observations might have reflected chance variations. We conclude that coexisting carbon aerosol did not increase respiratory irritancy of H₂SO₄, in most healthy and asthmatic subjects exposed for 1 hr under simulated "worst-case" ambient conditions.     

Characteristics of Individual Particles at a Rural Site in the Eastern United States

To determine the nature of aerosol particles in a rural area of the eastern United States, aerosol samples were collected at Deep Creek Lake, Maryland, on various substrates and analyzed by a scanning electron microscope (SEM) and a transmission electron microscope (TEM). SEM analysis of particles larger than 2.5 μm collected on Nuclepore filters revealed the following: clay minerals, quartz, gypsum, and calcite comprised 50 percent of the particles analyzed; spores, pollen, and plant debris comprised 25 percent; 9 percent were fly ash; 11 percent were sulfates; 5 percent were unidentified. Particles ranging from 0.3 to 2 μm were collected in a cascade impactor on grid-supported carbon films and analyzed by TEM for decomposition rate as well as for reaction with the barium chloride and nitron (C₂₀H₁₆N₄) films that were applied after sampling. The TEM analyses indicated that as much as 95 percent of the particles in the 0.3- to 2-μm diameter range were pure ammonium sulfate or acidic ammonium sulfate; they contained essentially no insoluble or nonvolatile matter. About 5 percent of the particles were fly ash spheres. When replicas of particles collected on Nucleopore filters were analyzed by TEM, we observed agglomerates of particles smaller than 0.1 μm.     

Measurements of Sulfur Oxides,Nitrogen Oxides,Haze and Fine Particles at a Rural Site on the Atlantic Coast

During August, 1982 and January and February, 1983, General Motors Research Laboratories operated air monitoring sites on the Atlantic Coast near Lewes, Delaware and 1250 km to the east on the southwest coast of Bermuda. The overall purpose of this project was to study the transformations of the principal acid precipitation precursors, NO _x and SO _x species, as they transport under conditions not complicated by emissions from local sources. In this paper, the measurements of gas and particulate species from Lewes are described and the composition and sources of sulfate aerosol, which is the most important haze-producing species, are investigated.

On the average, the total suspended particulate (TSP) concentration was 27.9 μg/m³ while the PM₁₀ (mass of particles with a diameter less than or equal to 10 μm) concentration was 22.0 μg/m³ or 79 percent of the TSP. The PM₁₀ consisted of 6.1 μg/m³ of coarse particles (CPM, diameter = 2.5 ? 10μm) and 15.9 μg/m³ of fine particles (FPM, diameter < 2.5 μm).

On a mass basis the most important constituents of the fine particulate fraction were sulfate compounds, 50 percent, and organic compounds, 30 percent. The mean light extinction coefficient corresponds to a visual range of 18-20 km. Most of the extinction can be attributed to the sulfate (60 percent) and organic carbon (13 percent). Particle size measurements show that the mass median aerodynamic diameter for both species is 0.43 μm. This is a typical size for a hydrated sulfate aerosol. For carbon, however, this is a larger size than previously reported and results in a more efficient light scattering aerosol. Principal component analyses indicate that coal combustion emissions from the midwestern U.S. are the most significant source of sulfate in Lewes during the summer and winter.     

Efflorescence relative humidity of airborne sodium chloride particles: A theoretical investigation

The previously developed theoretical model [Gao, Y., Chen, S.B., Yu, L.E., 2006. Efflorescence relative humidity for ammonium sulfate particles. Journal of Physical Chemistry A, 110, 7602–7608], which has successfully predicted the efflorescence relative humidity (ERH) of ammonium sulfate ((NH₄)₂SO₄) particles at room temperature, is employed to estimate the ERH of sodium chloride (NaCl) particles in sizes ranging from 6 nm to 20 μm. The theoretical predictions well agree with the reported experimental data in literatures. When the NaCl particles are larger than 70 nm, the ERH decreases with decreasing dry particle sizes, and reach a minimum around 44% RH, otherwise the ERH increases with decreasing dry particle sizes (<70 nm) because of the Kelvin effect. Compared with (NH₄)₂SO₄ particles, the Kelvin effect on ERH is stronger for NaCl particles smaller than 30 nm, while the dry particle size exerts weaker influence on NaCl particles larger than 70 nm.     

Removal of Ultrafine and Fine Particulate Matter from Air by a Granular Bed Filter

Abstract

The removal efficiency of granular filters packed with lava rock and sand was studied for collection of airborne particles 0.05–2.5 μm in diameter. The effects of filter depth, packing wetness, grain size, and flow rate on collection efficiency were investigated. Two packing grain sizes (0.3 and 0.15 cm) were tested for flow rates of 1.2, 2.4, and 3.6 L/min, corresponding to empty bed residence times (equal to the bulk volume of the packing divided by the airflow rate) in the granular media of 60, 30, and 20 sec, respectively. The results showed that at 1.2 L/min, dry packing with grains 0.15 cm in diameter removed more than 80% (by number) of the particles. Particle collection efficiency decreased with increasing flow rate. Diffusion was identified as the predominant collection mechanism for ultrafine particles, while the larger particles in the accumulation mode of 0.7–2.5 μm were removed primarily by gravitational settling. For all packing depths and airflow rates, particle removal efficiency was generally higher on dry packing than on wet packing for particles smaller than 0.25 μm. The results suggest that development of biological filters for fine particles is possible.     

Experimental studies on particle impaction and bounce: effects of substrate design and material

This paper presents an experimental investigation of the effects of impaction substrate designs and material in reducing particle bounce and reentrainment. Particle collection without coating by using combinations of different impaction substrate designs and surface materials was conducted using a personal particle sampler (PPS) developed by the University of Southern California. The PPS operates at flow rate of 4 l min^-1 with a 50% cutpoint of approximately 0.9 μm in aerodynamic diameter. The laboratory results showed that the PPS collection efficiency for particles larger than 50% cutpoint is strikingly low (e.g., less than 50%) when an uncoated open cavity made of aluminum was used as an impaction substrate. The collection efficiency gradually increased when Teflon tape, Nuclepore, and glass fiber filters were used as impaction surfaces, respectively. Conical or partially enclosed cavity substrate designs increased collection efficiency of particles of 9 μm up to 80–90%. A conical cavity with glass fiber filter used as impaction surface was identified as the optimum configuration, resulting in a collection efficiency of 92% at Stokes numbers as high as 15.4 (corresponding to 9 μm in aerodynamic diameter). Particle losses were low (less than 10%) and relatively independent of particle size in any design with glass fiber filter. Losses seemed to increase slightly with particle size in all other configurations. Finally, outdoor PM₁ concentrations obtained with the PPS (in its optimum configuration) and a modified micro-orifice uniform deposit impactor (MOUDI) with coated impaction stages were in excellent agreement. The mean ratio of the PPS-to-MOUDI concentration was 1.13(±0.17) with a correlation coefficient R²=0.95. Results from this investigation can be readily applied to design particle bounce-free impaction substrates without the use of coating. This is a very important feature of impactors, especially when chemical analysis of the collected particulate matter is desirable.     

Studies of the coarse particle (2.5–10 μm) component in UK urban atmospheres

An analysis is presented of continuous simultaneous measurement data for PM₁₀ and PM_2.5 using TEOM instruments from five sites in the United Kingdom. The results are analysed specifically in relation to the sources and processes influencing the coarse particle fraction (2.5–10 μm). The data show a generally strong correlation between fine and coarse particle concentrations at all sites, with a generally higher proportion of coarse particles in the dryer months of the year. The one rural site shows a notably lower proportion of coarse particles than the urban and suburban sites. Whilst it is possible to disaggregate the coarse particle concentrations into a component which is diluted by increasing windspeed and a component which increases with windspeed and is hence possibly attributable to wind-induced resuspension processes, the latter is only a minor proportion of the total coarse particle concentration. There are appreciable weekday-to-weekend and day-to-night differences between coarse particle concentrations which are most marked at the urban sites indicative of anthropogenic activities being a source of coarse particles. The clearest indication of the likely predominant source of coarse particles arises from an analysis of a data set derived from an urban street canyon site after subtraction of measurements from a nearby urban background location. The data indicate strong relationships of both fine and coarse incremental particle concentrations in the street canyon with incremental NO_x. If incremental fine particles and coarse particles are attributed to exhaust emissions and vehicle-induced resuspension, respectively, then it may be concluded that vehicle-induced resuspension provides a source strength approximately equal to that of exhaust emissions. An analysis of the coarse particle concentration data suggest that episodes of elevated coarse particle concentrations alone very rarely lead to exceedence of the UK air quality standard for PM₁₀ of 50 μg m⁻³ measured as a 24-h running mean.     

Experimental analysis of particle concentration heterogeneity in a ventilated scale chamber

The mixing processes of the aerosol particles from an outdoor environment in a ventilated scale chamber were experimentally studied. The particles were classified into five groups by size: 0.3–0.5 μm, 0.5–1.0 μm, 1.0–3.0 μm, 3.0–5.0 μm and 5.0–10.0 μm. The developing process for the concentration of each particle group was measured in different kinds of flow fields.The results show that the flow field configuration can effectively influence the dispersion time rate of the particles at certain positions. The increase in particle diameter can decrease the dispersion time rate. When the gas flow velocity is high, the particle dispersion time rate is independent of particle size; but when the gas flow velocity is low, particle size can significantly affect the particle dispersion time rate because the turbulent diffusion becomes important in the air and particle transport. The uniformity of the particle concentration for certain positions in steady state tends to be controlled by the inflow velocity, flow field configuration and the particle diameters.     

Product Guide/1982

Abstract

An efficient venturi scrubber system making use of heterogeneous nucleation and condensational growth of particles was designed and tested to remove fine particles from the exhaust of a local scrubber where residual SiH₄ gas was abated and lots of fine SiO₂ particles were generated. In front of the venturi scrubber, normal-temperature fine-water mist mixes with high-temperature exhaust gas to cool it to the saturation temperature, allowing submicron particles to grow into micron sizes. The grown particles are then scrubbed efficiently in the venturi scrubber. Test results show that the present venturi scrubber system is effective for removing submicron particles. For SiO₂ particles greater than 0.1 μm, the removal efficiency is greater than 80–90%, depending on particle concentration. The corresponding pressure drop is relatively low. For example, the pressure drop of the venturi scrubber is ～15.4 ± 2.4 cm H₂O when the liquid-to-gas ratio is 1.50 L/m³. A theoretical calculation has been conducted to simulate particle growth process and the removal efficiency of the venturi scrubber. The theoretical results agree with the experimental data reasonably well when SiO₂ particle diameter is greater than 0.1 μm.     

NH4+, NO3−, and SO42− in roadside and rural size-resolved particles and transformation of NO2/SO2 to nanoparticle-bound NO3−/SO42−

This study investigates ammonium, nitrate, and sulfate (NH₄⁺, NO₃^?, and SO₄^2?) in size-resolved particles (particularly nano (PM_0.01–0.056)/ultrafine (PM_0.01–0.1)) and NO_x/SO₂ collected near a busy road and at a rural site. The average (mass) cumulative fraction of secondary inorganic aerosols (SO₄^2?+NO₃^?+NH₄⁺) in nano or ultrafine particles at the roadside was found to be three to four times that at the rural site. The above three secondary inorganic aerosol species were present in similar cumulative fractions in particles of size 1–18 μm at both sites; however, dissimilar fractions were observed for Cl^?, Na⁺, and K⁺. The nitrogen ratios (NRs: NR = NO₃^??N/(NO₃^??N + NO₂–N)), sulfur ratios (SRs: SR = SO₄^2??S/(SO₄^2??S + SO₂–S)), dNR/D_P (derivative of NR with respect to D_P (particle diameter)), and dSR/D_P (derivative of SR with respect to D_P) at the roadside were higher than those at the rural site for nano/ultrafine particles. At both sites (particularly the roadside), the nanoparticles had significantly higher dNR/D_P and dSR/D_P values than differently sized particles, implying that NO₃^?/SO₄^2? (from NO₂/SO₂ transformation or NO₃^?/SO₄^2? deposition) were present on these particles.     

Diffusive transport through compacted Na- and Ca-bentonite

The effect of exchangeable cation — Na⁺ and Ca ²⁺ — on the diffusive transport of I⁻, Sr ²⁺ and ³H (as HTO) in compacted bentonite was examined using a through-diffusion method. Total intrinsic diffusion coefficients, D_i, were determined from the steady-state flux of the diffusants through the clays, and apparent diffusion coefficients, D_a, were obtained from the time lag technique. The clays were compacted to a dry bulk density of 1.3 Mg/m³, and Na-bentonite was saturated with a solution of 100 mol NaCl/m3 and Ca-bentonite with one of 50 mol CaCl₂/m³. The D_i values for all diffusants are 2 to 6 times higher in the Ca- than Na-clay. We attribute this to the larger quasicrystal, or particle, size of Ca- compared to Na-bentonite. Hence, Ca-bentonite has a greater proportion of relatively large pores; this was confirmed by Hg intrusion porosimetry. This means the diffusion pathways in Ca-bentonite are less tortuous than those in Na-bentonite. Moreover, in some cases the effective porosity, or the porosity available for diffusive transport, may be greater in Ca-bentonite. The D_a values are inversely proportional to the distribution coefficients of the diffusants with the clays.     

Composition and mixing state of the urban background aerosol in the Rhein-Main area (Germany)

Size-resolved aerosol particle samples in the size range 0.1–10 μm aerodynamic diameter were collected in the years 2003 and 2004 at an urban background station in Mainz, Germany. Size, morphology, chemical composition and mixing state of more than 5400 individual particles of 7 selected sampling days were analyzed in detail by scanning electron microscopy and energy-dispersive X-ray microanalysis. In addition, transmission electron microscopy, aerosol mass spectrometry and atomic force microscopy were applied to obtain detailed information about the mixing state of the particles. The fine particle fraction (diameter<1 μm) is always dominated by complex secondary aerosol particles (⩾90% by number) independent from air mass origin. These particles are complex internal mixtures of ammonium and sodium sulfates, nitrates, and organic material. Between 20% and 40% of the complex secondary aerosol particles contain soot inclusions. The composition of the coarse particle fraction (>1 μm diameter) is strongly dependant on air mass history with variable abundances of complex secondary aerosol particles, aged sea salt, silicates, silicate mixtures, calcium sulfates, calcium sulfate/carbonate mixtures, calcium nitrate/carbonate mixtures, biological particles, and external soot.The dominance of complex secondary aerosol particles shows that reduction of the precursor gases is a major goal for successful reduction strategies for PM₁₀.     

Characterisation of particulate matter and gaseous emissions from a large ship diesel engine

Composition of exhaust from a ship diesel engine using heavy fuel oil (HFO) was investigated onboard a large cargo vessel. The emitted particulate matter (PM) properties related to environmental and health impacts were investigated along with composition of the gas-phase emissions. Mass, size distribution, chemical composition and microphysical structure of the PM were investigated. The emission factor for PM was 5.3 g (kg fuel)^?1. The mass size distribution showed a bimodal shape with two maxima: one in the accumulation mode with mean particle diameter D_P around 0.5 μm and one in the coarse mode at D_P around 7 μm. The PM composition was dominated by organic carbon (OC), ash and sulphate while the elemental carbon (EC) composed only a few percent of the total PM. Increase of the PM in exhaust upon cooling was associated with increase of OC and sulphate. Laser analysis of the adsorbed phase in the cooled exhaust showed presence of a rich mixture of polycyclic aromatic hydrocarbon (PAH) species with molecular mass 178–300 amu while PM collected in the hot exhaust showed only four PAH masses.Microstructure and elemental analysis of ship combustion residuals indicate three distinct morphological structures with different chemical composition: soot aggregates, significantly metal polluted; char particles, clean or containing minerals; mineral and/or ash particles. Additionally, organic carbon particles of unburned fuel or/and lubricating oil origin were observed. Hazardous constituents from the combustion of heavy fuel oil such as transitional and alkali earth metals (V, Ni, Ca, Fe) were observed in the PM samples.Measurements of gaseous composition in the exhaust of this particular ship showed emission factors that are on the low side of the interval of global emission factors published in literature for NO_x, hydrocarbons (HC) and CO.     

The photochemical formation and gas–particle partitioning of oxidation products of decamethyl cyclopentasiloxane and decamethyl tetrasiloxane in the atmosphere

Decamethyl cyclopentasiloxane (D₅) and decamethyl tetrasiloxane (MD₂M) were injected into a smog chamber containing fine Arizona road dust particles (95% surface area <2.6 μM) and an urban smog atmosphere in the daytime. A photochemical reaction – gas–particle partitioning reaction scheme, was implemented to simulate the formation and gas–particle partitioning of hydroxyl oxidation products of D₅ and MD₂M. This scheme incorporated the reactions of D₅ and MD₂M into an existing urban smog chemical mechanism carbon bond IV and partitioned the products between gas and particle phase by treating gas–particle partitioning as a kinetic process and specifying an uptake and off-gassing rate. A photochemical model PKSS was used to simulate this set of reactions. A Langmuirian partitioning model was used to convert the measured and estimated mass-based partitioning coefficients (K_P) to a molar or volume-based form. The model simulations indicated that >99% of all product silanol formed in the gas-phase partition immediately to particle phase and the experimental data agreed with model predictions. One product, D₄TOH was observed and confirmed for the D₅ reaction and this system was modeled successfully. Experimental data was inadequate for MD₂M reaction products and it is likely that more than one product formed. The model set up a framework into which more reaction and partitioning steps can be easily added.