Atmospheric Size Distribution Research Articles

Evaluation of assumptions made by Hygroscopic Tandem Differential Mobility Analyzer inversion routines

The Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) measures the hygroscopicity of atmospheric particles, and many atmospheric processes that change this hygroscopicity also change the atmospheric size distribution. Two assumptions made during H-TDMA inversion create spurious hygroscopic trends as a function of the changing inlet size distribution. These two assumptions—that the particles exiting the first Differential Mobility Analyzer (DMA1) are singly charged and that the inlet size distribution has a slope of zero (flat)— generate Multi-Charge Dispersion (MCD) bias and Slope bias, respectively. First, we use a model, named TAO, to show that the inlet size distribution could theoretically change the measured ammonium sulfate hygroscopicity by 10%–20% as a function of diameter or experimental time with no change in relative humidity. Secondly, we show experimentally that aerosol emitted from the flaming combustion of grass creates MCD bias. In this experiment, we measure the CPC response of the first three charges and invert these responses using a new routine named Junior. Junior's inversion of each charge shows that one growth factor distribution describes all measured diameters (no growth dependence on diameter). As in the modeling study above, previous publications of this aerosol system, using traditional inversion assumptions, report a decrease in hygroscopicity as DMA1 diameter increases. Unlike traditional inversions, Junior's inversion does not assume the particles are singly charged nor does it make the flat inlet size distribution assumption. Instead, both the inlet size distribution and each charge's CPC response are measured quantities. Thus, the discrepancy between our inversion results and previous publications is likely due to the traditional inversion routine assumptions. This underscores the importance for accounting for Slope and MCD bias during inversions. Experimental results should be carefully analyzed when reporting hygroscopic trends with respect to diameter or experimental time when using the traditional inversion assumptions.

Airborne microplastic particles detected in the remote marine atmosphere

Anthropogenic pollution from marine microplastic particles is a growing concern, both as a source of toxic compounds, and because they can transport pathogens and other pollutants. Airborne microplastic particles were previously observed over terrestrial and coastal locations, but not in the remote ocean. Here, we collected ambient aerosol samples in the North Atlantic Ocean, including the remote marine atmosphere, during the Tara Pacific expedition in May-June 2016, and chemically characterized them using micro-Raman spectroscopy. We detected a range of airborne microplastics, including polystyrene, polyethylene, polypropylene, and poly-silicone compounds. Polyethylene and polypropylene were also found in seawater, suggesting local production of airborne microplastic particles. Terminal velocity estimations and back trajectory analysis support this conclusion. For technical reasons, only particles larger than 5 µm, at the upper end of a typical marine atmospheric size distribution, were analyzed, suggesting that our analyses underestimate the presence of airborne microplastic particles in the remote marine atmosphere.

Particle emissions characterization from a medium-speed marine diesel engine with two fuels at different sampling conditions

Particle emission characteristics for a medium-speed four-stroke marine diesel engine were studied using a variety of sampling systems. Measurements were conducted at 25% and 75% load employing a heavy fuel oil (HFO) and a lighter marine distillate oil. The measurements, especially with HFO, revealed that marine exhaust particles mostly consist of nanometer sized ash particles on which heavy volatile species condense during exhaust dilution and cooling. The soot mode number concentration was low with both fuels tested, in particular when HFO was used. Total particle number emissions ranged in the order of 5.2–6.9×1015 per kg of fuel and formed a monomodal size distribution when a porous tube diluter combined with an ageing chamber and operating at low dilution ratio was used for sampling. The levels and size distributions obtained in the lab using a porous tube diluter were similar to the ones reported in the literature studying ship plumes following atmospheric dilution. Lab measurements with ejector-type diluters mostly led to bi-modal distributions that did not well resemble atmospheric size distributions. Moreover, the nucleation mode formed with the ejector diluters was variable in size and concentration. When used with dilution air at ambient temperature, ejector diluters were inappropriate for primary dilution due to clogging.

Seasonal variation of particle size distributions of PAHs at Seoul, Korea

The atmospheric size distributions of particulate polycyclic aromatic hydrocarbons (PAHs) up to 10 μm in diameter were measured at Seoul in the summer and winter of 2003. The concentrations of total PAHs were from 4.32 to 5.48 ng m−3 in summer and from 25.6 to 35.9 ng m−3 in winter, respectively. Majority of the PAHs concentrations were found on fine particles (D p < 2.1 μm). The size distributions of individual PAH compounds were bimodal with the peaks in the 0.43–0.65- and 4.7–5.8-μm range in summer. In winter, those were unimodal or weakly bimodal with the peaks in the 0.65–1.1- and 4.7–5.8-μm range. The seasonal variation of the peak size range in the fine mode might be caused by longer residence time in the air in winter. Based on the previously reported source diagnostic ratios of PAHs for the major emission sources, it was suggested that vehicles were the major source of PAH in summer, while coal-related emissions and firewood fire were the major sources in winter for fine particles. The seasonal variation of the peak size ranges in the fine particles had not shown noticeable effect on the dry deposition fluxes. However, it might affect the optical properties of the atmosphere.

Potential climatic effects of meteoric smoke in the Earth's paleo‐atmosphere

Modelling of the growth of meteoric smoke in the Earth's atmosphere, by assuming the formation of either simple spherical (compact) particles or, more realistically, fractal (porous) aggregates, highlights important differences in the predicted atmospheric size distributions as a function of altitude. The calculated UV extinction and direct radiative forcing (DRF) of these types of particles is also quite different. It is shown that, with regard to (a), forming a UV barrier before the presence of significant ozone levels in the atmosphere and (b), triggering ‘snowball Earth’ glaciations by negative DRF, fractal smoke particles are unlikely to have been important even if the flux of interplanetary dust into the atmosphere was 3 orders of magnitude higher than the present day. However, if these particles are effective ice nuclei, then subsequent indirect forcing through ice cloud formation could have made a more significant contribution to the onset of ancient glaciation episodes.

Atmospheric dry deposition of trace elements measured around the urban and industrially impacted NY–NJ harbor

Long-term direct trace metal dry deposition measurements were made during 2001 and 2002 at two sites near the NY/NJ Harbor Estuary in New Jersey: Jersey City (JC) and New Brunswick (NB). In addition intensive dry deposition and atmospheric size distribution (ASD) measurements were made between September 2001 and June 2002. Dry deposition samples were obtained using modified MIC-B wet deposition samplers which deployed knife-edge surrogate surfaces during dry periods. ASDs were measured with micro-orifice uniform deposit impactors (MOUDI) and coarse particle rotary impactors (CPRI). The fluxes of trace metals were found to be highest at the JC site and lowest at the NB site. The dry deposition fluxes ranged from 0.030 (Cd) to 3800 (Al) μg m −2 d −1 and 0.14 (Cd) to 8100 (Al) μg m −2 d −1at NB and JC sites, respectively. Metals of crustal origin were found mostly in the coarse particle fraction and anthropogenic metals were found mostly in the fine particle fraction. For the intensive experiments, overall dry deposition velocities of several trace metals were determined by dividing measured fluxes by measured concentrations in different particle size ranges. For most of the elements, the flux was highly correlated with PM 10 and coarse particle concentrations. The overall dry deposition velocities of crustal elements (Al and Mg) varied from 3.7 to 8.7 cm s −1 with correlation coefficients ranging from 0.50 to 0.84. The best-fit dry deposition velocities for anthropogenic elements (Cr, Mn, Zn, and Pb; Cu, Mo, and Ba; V and Ni) varied more than those for crustal elements (0.52–25 vs. 3.7–8.7 cm s −1). The dry deposition velocities for most elements obtained using three size ranges were statistically significant with R 2 values ranging from 0.37 to 0.84 except for V and Ni (0.12).

Size Distributions and Dry Deposition Fluxes of Particulate Polycyclic Aromatic Hydrocarbons (PAHs) at Several Sites in Korea in 1999

The atmospheric size distributions of particulate polycyclic aromatic hydrocarbons (PAHs) and their deposition fluxes were measured at four sites in August and at three sites in November 1999, in Korea. The total ambient particulate PAHs concentrations at each site ranged between 6.7 and 128.7 ng m−3. In November, the total PAHs concentrations at Inchon (IC) were the highest, followed by Yangsuri (YS) and Seoul (SE). This trend is contrary to the expectation that the total PAHs concentrations at IC and SE be higher than that at YS because IC and SE are highly industrialized large cities and YS is rural area. The size distributions of individual PAHs in IC and SE show trimodal in Dp ≤ 9 µm while the particulate PAHs in YS were distributed evenly to fine- and coarse-size particles. These results suggest that YS has local sources in addition to transport of PAHs emitted from urban sources. The measured dry deposition fluxes of total PAHs ranged from 6.9 to 12.6 µg m−2 day−1 in August, and from 5.9 to 8.5 µg ...

Atmospheric Size Distribution of PAHs: Evidence of a High-Volume Sampling Artifact

The purpose of this study was to characterize atmospheric levels of four- to six-ring polycyclic aromatic hydrocarbons (PAHs) in the vicinity of a horizontal stud Söderberg aluminum smelter in terms of the size distribution of particulate matter (September to December 2002). It was found that the vast majority of the PAHs was associated with particle diameters less than 1 and 3 microm. A profile comparison of the PAH mixture--using benzo[a]pyrene (B[a]P) relative abundance ratios (PAH/B[a]P)--for the cascade impactor filters indicated the formation of a sampling artifact. Overall, the PAH stability scale generated in this study agrees with those produced experimentally for ozone and nitrogen dioxides or developed using other in situ measurement techniques. Correlations of the four- to six-ring PAHs with other atmospheric variables suggested that smelter plume conditions and particle characteristics may play a potentially important role in the overall PAH reactivity. To our knowledge, this is the first study to report a sampling artifact for the four- to six-ring PAHs during in situ high volume sampling under real world conditions.

Size distribution and dry deposition of particulate mass, sulfate and nitrate in an urban area

Atmospheric size distributions for mass, sulfate and nitrate were measured in Chicago, Illinois during the Spring–Summer, and Fall of 1994 and 1995. Nineteen samples were collected over two or three daytime periods using a Wide Range Aerosol Classifier system (Noll Rotary Impactor and Cascade Impactor). The Atmospheric Aerosol was divided into 10 size range between 0.1 and 100 μm. The total particulate mass contains three peaks, a fine peak (mode) with an MMD of 0.43 μm, and two coarse particulate peaks at 6.75 (mode 2) and 28.58 μm (mode 3). The total concentration of particles and the location of the concentration peaks varied significantly depending on wind velocity. Data shows that sulfate and nitrate existed in both the fine (<2.5 μm) and coarse (>2.5 μm) particles. The atmospheric concentration of sulfate in the fine and coarse particles varied between 1.0–7.0 and 0.3–1.0 μg/m 3, respectively. The nitrate concentrations were 0.3–5.3 μg/m 3 in the fine and 0.3–2.9 μg/m 3 in the coarse fraction. Dry deposition fluxes were simultaneously measured with a knife edged surrogate surface containing greased mylar films. The measured dry deposition fluxes of sulfate and nitrate were between 1.0–4.0 and 0.5–3.9 mg/(m 2 day), respectively. A multi-step method was used to calculate total and cumulative deposition flux with the Semhel–Hodgson deposition velocity model and atmospheric particulate concentration. The results indicated that calculated flux compares well with measured flux, and greater than 99% of the total flux was due to particles larger than 5 μm diameter for both sulfate and nitrate. The average ratios of calculated/measured fluxes were 0.93 for sulfate and 0.91 for nitrate.

Primary particle emissions from residential coal burning: Optical properties and size distributions

Particles generated by combustion of fossil fuels contribute to climate forcing by absorbing and scattering visible light. Residential combustion takes place in homes for heating or cooking purposes and is thought to contribute a large fraction of the global burden of anthropogenic primary particles. We present optical properties and size distributions of particulate matter emitted from three types of coal burned in residential combustors: bituminous coal, hard coal briquettes, and lignite. Emissions from these coals differ significantly and can be partially explained by differences in coal composition. For bituminous coal, particulate matter emission factors are somewhat greater than those used in current emission inventories. We observe particles for which the light absorption is weak and has a strong spectral dependence. For hard coal briquettes and lignite, emitted light absorption is low, and based on our measurements, current inventories of light‐absorbing aerosols significantly overestimate the contribution from these sources. Hard coal briquettes produce very few particles in the optically active size range. For all coals tested the size distributions required to represent the average of the emitted particles are broader than atmospheric size distributions, with geometric standard deviations between 2.2 and 3.0.

Dry Deposition Fluxes and Mass Size Distributions of Pb, Cu, and Zn Measured in Southern Lake Michigan during AEOLOS

As part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS) the dry deposition fluxes and atmospheric size distributions (ASDs) of anthropogenic metals were measured over the southern basin of Lake Michigan. The measurements were made during winter, summer, and fall, concurrently, in Chicago, IL; over Lake Michigan onboard the U.S. EPA RV Lake Guardian; and in South Haven, MI. The flux of Pb, Cu, and Zn was substantially higher in Chicago than in either South Haven or over Lake Michigan. The average measured Pb, Cu, and Zn fluxes were 0.07, 0.06, and 0.20 mg/m 2 .day in Chicago; 0.003, 0.01, and 0.01 mg/m 2 .day over Lake Michigan; and 0.004, 0.007, and 0.004 mg/m 2 .day in South Haven. When the wind was from Chicago over the lake, the fluxes and concentrations measured over the lake were higher than when the wind was from other directions. In general, these anthropogenic metals had higher concentrations in the fine particle mode than in the coarse particle mode. Modeled and measured fluxes were in reasonable agreement. Coarse particles were found to be responsible for the majority of the flux at all locations.

Dry Deposition Fluxes and Atmospheric Size Distributions of Mass, Al, and Mg Measured in Southern Lake Michigan during AEOLOS

ABSTRACT In this study, which was a part of the Atmospheric Exchange Over Lakes and Oceans Study (AEOLOS) investigation, the dry deposition fluxes and atmospheric size distributions (ASDs) of mass and crustal metals (aluminum and magnesium) were measured over the southern basin of Lake Michigan (in Chicago, over Lake Michigan, and in South Haven, Michigan). Airborne crustal metals arise primarily from fugitive dust emissions and are associated with the coarse fraction of atmospheric aerosol. Consequently, they can serve as fingerprints for the atmospheric behavior of fugitive dust. The flux of these metals were substantially higher in Chicago than in either South Haven or over Lake Michigan. The measured average mass, aluminum, and magnesium fluxes were 138, 2.23, and 5.32 mg/m2-day in Chicago, 47.8, 0.24, and 0.28 mg/m2-day over Lake Michigan, and 37.4, 0.17, and 0.12 mg/m2-day in South Haven, respectively. The ASDs of crustal metals measured in Chicago had higher concentrations of coarse particles than ASDs measured over Lake Michigan and in South Haven. The calculated flux of metals using a multistep model and dry deposition velocities obtained from the Sehmel-Hodgson model were in general agreement with measured fluxes of crustal metals. Particles >10 μm were found to be responsible for the majority of the flux.

Atmospheric Size Distributions Measured by Differential Mobility Optical Particle Size Spectrometry

ABSTRACT A differential mobility and optical particle size spectrometer (DMOPSS) was developed to measure ambient size distributions based on geometric particle diameter in the size range of 0.1 to 1.0 μm diameter. The DMOPSS consists of a high-flow differential mobility analyzer (HF-DMA) followed by an optical particle counter (OPC) and condensation nucleus counter (CNC) operating in parallel. The OPC and CNC sample monodisperse aerosol of known geometric diameter from the HF-DMA output or, alternatively, polydisperse aerosol with known dilution directly from the ambient air. The monodisperse samples are used to create time-dependent calibrations of the OPC, providing optical response versus geometric size for the ambient aerosol under study. The direct ambient measurements are then reduced, using this ambient-based calibration. A field test of the DMOPSS system was performed in the summer of 1992 at Meadview, Arizona, where more than 12,000 size spectra were collected; they consisted of roughly one-third direct ambient samples and two-thirds HF-DMA sized samples. Measured aerosol volumes and calculated particle scattering coefficients were strongly correlated with nephelometer measurements, with a mean scattering-to-volume ratio of 5 m2/cm3. With the ambient aerosol calibration, the measured aerosol volumes were 47% larger, and volume geometric mean diameters were 12% larger, than would have been obtained using a polystyrene latex calibration.

Accurate measurements of aerosol size distribution—II. Construction of a new plate condenser electric mobility analyzer and first results

Design details and exact values of electrostatic and stream fields of a new plate condenser mobility analyzer described elsewhere (Haaf,1980) are given. The conditions for thermal stability and laminarity of the respective flows are tested. Independent calibrations of the device are performed. Initial atmospheric size distribution measurements indicate that the true fraction charged for particles in the lower Aitken range lies between the Boltzmann law and the theory following Gentry (1972).

Calculated Distribution Characteristics for a Reinforced Coagulating Aerosol at Steady State

Abstract The steady-state number balance for a reinforced coagulating aerosol, with particle removal at some selected size, was solved as a continuous function of particle volume. Using a variety of log-normal feed distributions, it was demonstrated that a power law relationship will result between particle concentration n(v) and volume v, regardless of feed distribution shape. The standard deviation σ of the feed distribution was varied from 1.21 to 20.09. The slopes of the calculated distributions varied with σ. For values of σ 8.0 the slope approached −1.0. Calculated distribution slopes for σ < 2 were similar to those of atmospheric distributions reported for stable meteorological conditions. The time to reach steady state was estimated and found not to be unreasonable compared to meteorological time scales. The results suggest that the Junge power law relationship observed in many atmospheric size distributions may be explained principa...

The aerosol size distribution of Los Angeles smog

A total of 342 atmospheric size distributions have been measured at the California Institute of Technology in Pasadena, CA during August and September 1969 over the size range 0.003–6.8 μm using the Minnesota Aerosol Analyzing System in collaboration with other investigators making chemical, meteorological, mass, and optical measurements. This paper presents characteristics of the aerosol size distributions and discusses the significance of these findings. It also presents a new computer-compatible system of nomenclature and a new system for separating and analyzing the size distribution in one decade ranges. In addition to the usual log ΔN/ ΔD p versus log D p plot, it was found that a plot of ΔV/ Δ log D p versus log D p was very useful for characterizing the distribution of particles larger than 0. 05 μm. From the later volume distribution plot, it was found that the smog aerosol was universally bimodal with the saddle point in the 1- to 2-μm size range and with the volume fraction for the individual size distributions below 1 μm being characterized with a grand correlation coefficient of 0.9719 with log normal distributions. The grand log normal distribution had a geometric mean of 0.302 μm and a geometric standard deviation of 2.25. The grand average volume below 1.05 μm was 34 μm 3/cm 3 and the volume above 1.05 μm was 24.1 μm 3/cm 3. For sizes above 1 μm, the volume distribution increases steadily up to 6.8 μm, the largest size measured by the MAAS. Comparisons with Lundgren impactor data suggest that this larger mode peaks at 7–10 μm and then drops sharply at about 15 μm. The grand average number distribution log ΔN/ ΔD p vs. log D p was very similar to the grand average measured by Clark and Whitby in Minneapolis in 1966. The number distribution can be characterized reasonably well in the size range from 0. 2 to 7 μm by ΔN/ ΔD p = 0. 4 VT D p −4, where VT = 58. 1 μm 3/cm 3, the total volume fraction. The volume fraction smaller than 1. 05 μm was found to correlate well with light scattering, solar radiation, and, to a lesser degree, with ozone. Analysis of the data and comparisons with laboratory studies of coagulating aerosols suggest strongly that, during the daytime when there is even light smog, most of the aerosol mass, in the size range smaller than 1 μm, is contributed by condensation of photochemical reaction products on particles larger than 0. 1 μm rather than from coagulation of smaller particles. There is considerable evidence that, while most of the mass of particles smaller than 1 μm is contributed by photochemical reactions during smog periods, most of the mass of particles larger than a few microns comes from other sources. While the aerosol mass of particles smaller than 1 μm peaks at about noon, the maximum in the condensation nuclei count peaked at about 1500 at values on the order of 1. 8 × 10 5/cm 3. On the other hand, in Minneapolis, when there was no volume peak at noon, the condensation nuclei count peaked at 1. 8 × 10 6/cm 3. The third paper in this series shows that, because the coagulation coefficient between 0. 01-μm particles and the 0.3-μm particles of the lower volume mode is much higher than for 0.01-μm particles with themselves, the presence of the relatively large volume below 1 μm in Los Angeles smog decreases the maximum condensation nuclei count observed compared to cities with less severe air pollution.