Average Aerosol Concentration Research Articles

Effect of the summer monsoon on aerosols at two measurement stations in Northern India – Part 2: Physical and optical properties

Abstract. Aerosol physical and optical properties were measured at two locations in northern India. The first measurement station was a background site in Mukteshwar, about 350 km northeast of New Delhi, in the foothills of the Indian Himalayas, with data from 2006 to 2009. The second measurement site was located in Gual Pahari, about 25 km south of New Delhi, with data from 2008 to 2009. At both stations, the average aerosol concentrations during the monsoon were decreased by 40–75 % compared to the pre-monsoon average concentrations. The decrease varied with the total local rainfall. In Mukteshwar, the monsoon season removed particles from all size classes, due to a combination of rain scavenging and activation to cloud and mountain fog droplets. The scavenging by rain is least effective for the size range of the accumulation mode particles. In Gual Pahari, this was the only major wet removal mechanism and, as a result, the accumulation mode particles were less effectively removed. Aerosol concentrations during the early monsoon were found to be affected by mineral dust which in Gual Pahari was observed as an increased particle volume at a diameter around 3–4 μm. The single scattering albedo varied from 0.73 to 0.93 during the monsoon season, being slightly lower in Gual Pahari than in Mukteshwar. This is due to the fact that Gual Pahari resided closer to high anthropogenic black carbon emissions. As the absorbing particles are typically in the accumulation mode, they were not effectively removed by rain scavenging. The aerosol columnar properties, which were measured in Gual Pahari, showed a somewhat different seasonal behaviour compared to the surface measurements, with the aerosol optical depth increasing to an annual maximum in the early monsoon season.

Long-term in situ measurements of the cloud-precipitation microphysical properties over East Asia

A database of cloud-precipitation microphysical characteristics is established, using in situ data during 1960–2008. Main features of aerosol, ice nuclei (IN), cloud droplet, fog, ice crystal, snow crystal, and raindrop are presented based on the analyses of the database. In addition, a statistical analysis has been performed. The results show that the overall average aerosol concentration in diameter greater than 0.3 μm is 166.9 cm −3 and the average maximum values of IN concentration can reach 78.9 L −1 at − 20 °C, with an overall average of 22.9 L −1. In addition, cumuliform clouds have higher overall average cloud droplet number concentration (N c) of 907.7 cm −3, and that of stratiform clouds, is 120.9 cm −3; cumuliform clouds (stratiform clouds) have an average liquid water content (LWC) of 0.875 (0.140) g m −3, with a peak value of 2.000 (0.520) g m −3. The gamma size distributions are shown to be suitable for most of the observed spectra in stratiform clouds. Both the exponential and gamma size distributions are applicable to fit the raindrops originating from stratiform clouds. Good agreement is obtained when the gamma size distribution is applied to fit the raindrops originating from both convective and mixing (stratiform and cumuliform) clouds. The exponential size distributions are suitable for both ice crystal and snow crystal fitting.

Size-fractionated water-soluble ions, situ pH and water content in aerosol on hazy days and the influences on visibility impairment in Jinan, China

To study the size-fractionated characteristics of aerosol chemical compounds including major water-soluble inorganic and organic ions, situ pH and water content as well as their influences on visibility, field sample collections using a Micro Orifice Uniform Deposit Impactor (MOUDI) combined with simulations by Aerosol Inorganic Model (AIM) were conducted on hazy and clear days in Jinan, China from April, 2006 to January, 2007. Average concentrations of TSP, PM 10 and PM 1.8 on hazy days were found to be 1.49–5.13, 1.54–5.48 and 1.30–5.48 times those on clear days during the sampling periods, indicating that particulate pollution was very serious on hazy days. Size distributions of mass, SO 4 2− , NO 3 − , formate and acetate were all bimodal with fine mode predominant on hazy days, demonstrating that fine particles and secondary pollutants were more easily formed on hazy days. The average total aerosol concentration of H + ([H + ] total ), of which free H + concentration ([H + ] ins ) inside aerosol accounted for 30%, was 2.36–4.21 times that in other cities in China and US. The [H + ] ins on hazy days was 2.43–13.11 times that on clear days and the estimated situ pH was mainly influenced by RH and mole ratios of [NH 4 + ]/[SO 4 2− ]. Size distributions of situ pH were unimodal peaked at 0.56 μm on clear days in spring and autumn as well as on hazy days in autumn, while a trend of increasing was shown on hazy days in spring and summer. The normalized water content (NWC) was higher on hazy days in autumn and winter because of the easier uptake of water by aerosol. It was found that when NWC < 2, if [NH 4 + ]/[SO 4 2− ] < 2.0, aerosol chemical components were more sensitive to water content, while if [NH 4 + ]/[SO 4 2− ] > 2.0, relative humidity (RH) was more important. Size distributions of water content showed a trend of sharp increasing on hazy days in spring and autumn. Correlation and regression analysis indicated that visibility was significantly influenced by the concentrations of SO 4 2− and water content in the range of 1.0–1.8 μm. ► Influences of size fractionated aerosol chemical compounds on visiblity were studied. ► Secondary ions and fine particles were more easily formed on hazy days. ► Aerosol acidity on hazy days was stronger than that on clear days. ► Aerosol absorbed water more easily on hazy days. ► SO 4 2− and water content in 1–1.8 μm were the major factors to reduce visibility.

Assessing the Impact of Industrial Source Emissions on Atmospheric Carbonaceous Aerosol Concentrations Using Routine Monitoring Networks

Industrial sources can have a significant but poorly defined impact on ambient particulate matter concentrations in select areas. Detailed emission profiles are often not available and are hard to develop because of the diversity of emissions across time and space at large industrial complexes. A yearlong study was conducted in an industrial area in Detroit, MI, which combined real-time particle mass (tapered element oscillating microbalance) and black carbon (aetholometer) measurements with molecular marker measurements of monthly average concentrations as well as daily concentrations of select high pollution days. The goal of the study was to use the real-time data to define days in which the particulate matter concentration in the atmosphere was largely impacted by local source emissions and to use daily speciation data to derive emission profiles for the industrial source. When combined with motor vehicle exhaust, wood smoke and road dust profiles, the industrial source profile was used to determine the contribution of the local industrial source to the total organic carbon (OC) concentrations using molecular marker-chemical mass balance modeling (MM-CMB). The MM-CMB analysis revealed that the industrial source had minimal impact on the monthly average carbonaceous aerosol concentration, but contributed approximately 2 [H9262]g m-3, or a little over one-third of the total OC, on select high-impact days.

Characterization of a head-only aerosol exposure system for nonhuman primates

A well-characterized exposure chamber is necessary to generate reproducible atmospheres for inhalation toxicology studies. The aim of the present study was to characterize a head-only exposure chamber for non-human primates. Aerosols containing bovine serum albumin (BSA) were used to characterize a 16-L dynamic airflow head-only exposure chamber. A 250-ml plastic bottle with a respirator attached located inside the chamber was used to simulate a breathing head. Chamber leak rate, mixing, and aerosol spatial distributions were quantified. The chamber concentration profile was measured at the chamber exhaust using an aerodynamic particle sizer. Aerosol spatial distribution was determined by collecting filter samples at several chamber locations. The particle size distribution was determined by collecting cascade impactor samples at several chamber locations. The estimated chamber leak rate was within standards suggested in the literature. The measured average aerosol residence time was similar to theoretical aerosol residence time, suggesting that the chamber was mixing well. Additionally, the average concentration measured at each of the sampling locations within the chamber was similar, and the within-run coefficients of variation (CV) across all sampling locations was similar to those reported in previously published studies, again suggesting that the aerosol concentration throughout the chamber was uniform. The particle size distribution was similar throughout the exposure chamber. Additionally, the BSA concentration and particle size distributions measured in the breathing zone of the simulated head were not significantly different from measurements made elsewhere in the chamber, suggesting that respiration does not affect the average aerosol concentration or particle size distribution at the mouth.

Observations of marine stratocumulus microphysics and implications for processes controlling droplet spectra: Results from the Marine Stratus/Stratocumulus Experiment

During the Marine Stratus/Stratocumulus Experiment, cloud and aerosol microphysics were measured in the eastern Pacific off the coast of northern California on board Department of Energy Gulfstream‐1 in July 2005. Three cases with uniform aerosol concentration and minimal drizzle concentration were examined to study cloud microphysical behavior. For these three cases, the average droplet number concentration increased with increasing altitude, while the average interstitial aerosol concentration decreased with altitude. The data show enhanced growth of large droplets and spectral broadening in cloud parcels with low liquid water mixing ratio. Three mixing models, including inhomogeneous mixing, entity type entrainment mixing, and circulation mixing proposed in this study, are examined with regard to their influences on cloud microphysics. The observed cloud microphysical behavior is most consistent with the circulation mixing, which describes the mixing between cloud parcels with different lifting condensation levels during their circulations driven by evaporative and radiative cooling. The enhanced growth and spectrum broadening resulting from the circulation mixing reduce cloud albedo at the same liquid water path and facilitate the formation of precipitation embryos.

The concentration and number size distribution measurements of the Marine Boundary Layer aerosols over the Indian Ocean

The measurements of total number concentration and number size distribution of aerosols in size ranges of 16–700 nm and 0.5–20 μm diameters made from 14°N to 56°S in the Indian ocean during January 23 to March 31, 2004, are reported. The average values of total number (mass) concentration of micrometer aerosols (0.5–20 μm) are 7.2 ± 3 cm − 3 (8.89 µg m − 3) from 14°N to the Inter-Tropical Convergence Zone (ITCZ), 4.6 ± 2 cm − 3 (4.9 µg m − 3) in the ITCZ, 3.0 ± 1.4 cm − 3 (5.78 µg m − 3) in the trade wind region from 8°–30°S, 3.8 ± 2.6 cm − 3 (7.9 µg m − 3 ) from 30°–40°S, and 5.8 ± 3.5 cm − 3 (9.65 µg m − 3) in the roaring forties from 40°–56°S. Latitudinal distribution of such aerosols shows that their number concentration is minimum (0.5 cm − 3 ) at 11°S and increases on either side of this location. Size distributions of micrometer aerosols in all latitudinal belts show a maxima in coarse mode at 0.5–1.5 μm diameter. The correlation coefficient in the aerosol concentration–wind speed relations of these aerosols is observed to differ in different latitudinal belts and has maximum value in the belt of strongest winds. Also, diurnal variations of the average aerosol concentration and wind speed show some similarity in belts of strong winds. Total number concentration of submicrometer (16–700 nm) particles is also minimum in the southern trade wind region and their size distribution is bimodal with maxima in Aitken mode (~ 50 nm) and accumulation mode (~ 130 nm). South of the ITCZ, concentrations of both, total number and Aitken mode particles normally increase with latitude. The increase in Aitken mode particles at high latitudes is large enough for the Aitken mode maxima to superimpose the accumulation mode maxima. Observations suggest that addition of Aitken particles is so fast that process of coagulation is not able to reach equilibrium to develop a distinct accumulation maxima. Observations show that pristine air of the trade wind region in the Southern Hemisphere can be advected to mid-latitudes along the ridge developed between anticyclonic and cyclonic systems.

Aircraft observations of aerosol composition and ageing in New England and Mid‐Atlantic States during the summer 2002 New England Air Quality Study field campaign

Aerosol chemical composition, size distribution, and optical properties were measured during 17 aircraft flights in New England and Middle Atlantic States as part of the summer 2002 New England Air Quality Study field campaign. An Aerodyne aerosol mass spectrometer (AMS) was operated with a measurement cycle of 30 s, about an order of magnitude faster than used for ground‐based measurements. Noise levels within a single measurement period were sub μg m−3. Volume data derived from the AMS were compared with volume measurements from a Passive Cavity Aerosol Spectrometer (PCASP) optical particle detector and a Twin Scanning Electrical Mobility Spectrometer (TSEMS); calculated light scattering was compared with measured values from an integrating nephelometer. The median ratio for AMS/TSEMS volume was 1.25 (1.33 with an estimated refractory component); the median ratio for AMS/nephelometer scattering was 1.18. A dependence of the AMS collection efficiency on aerosol acidity was quantified by a comparison between AMS and PCASP volumes in two high sulfate plumes. For the entire field campaign, the average aerosol concentration was 11 μg m−3. Compared with monitoring data from the IMPROVE network, the organic component made up a large fraction of total mass, varying from 70% in clean air to 40% in high concentration sulfate plumes. In combination with other optical and chemical measurements, the AMS gave information on secondary organic aerosol (SOA) production and the time evolution of aerosol light absorption. CO is taken as a conservative tracer of urban emissions and the ratios of organic aerosol and aerosol light absorption to CO examined as a function of photochemical age. Comparisons were made to ratios determined from surface measurements under conditions of minimal atmospheric processing. In air masses in which the NOx to NOy ratio has decreased to 10%, the ratio of organic aerosol to CO has quadrupled indicating that 75% of the organic aerosol is secondary. Also, the ratio of light absorption to CO has more than doubled, which is interpreted as an equivalent increase in the light absorption efficiency of black carbon due to aerosol ageing.

The importance of cloud drop representation on cloud photochemistry

Because the acidity of the drop varies with cloud drop size, the concentration of species whose dissolution or whose aqueous reactions depend on the pH of the drop may also depend on the manner the cloud drop size distribution is represented in the cloud model. Cloud parcel model simulations coupled with gas and aqueous-phase chemistry are performed to assess the importance of the cloud drop size distribution on aqueous photochemical species. This study focuses on sulfate, sulfur dioxide, hydrogen peroxide, ozone, formaldehyde, and formic acid because these species concentrations can be dependent on the pH of the cloud drops. In one set of simulations the cloud drop size distribution is represented explicitly, that is, sectioned into sizes using the bin method. In a second set of simulations, the cloud drop size distribution is represented by a single-sized drop with radius = 10 μm, which is a common assumption in cloud physics models. The cloud parcel model simulations are computed with and without the coalescence process. Simulations without coalescence show that predicted formaldehyde and formic acid mixing ratios are affected by the cloud drop size distribution particularly in average background aerosol concentrations. Effects on other species are small. Results from simulations that included the coalescence process (resulting in a broader cloud drop size distribution) have similar results as the no coalescence simulations. Due to entrainment and turbulence processes, cloud water size distributions measured in clouds are generally broader than those modeled in this study. Thus, the effect of these processes on cloud photochemistry needs to still be assessed.

Using NOx and CO monitoring data to indicate fine aerosol number concentrations and emission factors in three UK conurbations

Abstract It is increasingly accepted that although exposure to elevated concentrations of PM10 is associated with an increased risk of mortality and morbidity, the relationship may not be causal. Rather, there is evidence that number concentrations may be a more appropriate metric than mass concentrations in evaluating health risk. Number concentrations are not routinely monitored and spatial and temporal patterns are poorly quantified. CO and NOx are co-pollutants with their major urban source in common with fine particles, i.e. road vehicle emissions; are routinely monitored in many cities and are also related to ill health. Datasets of particle number concentration measurements from approximately month-long field campaigns in Manchester, Edinburgh and Birmingham (UK) are compared with simultaneous concentrations of CO and NOx from nearby fixed monitors. It was found that it might be possible to reliably predict particle number concentrations (diameters>100 nm) on an hourly basis in Manchester city centre from knowledge of NOx or CO concentrations alone. The influences of meteorology, spatial variability in emissions and lack of co-location upon the correlations are investigated using cluster analysis. The cluster analysis revealed that these relationships may vary between cities and are dependent upon monitor location but in ways that can be ascribed. For two out of three sites there existed a linear relationship between average cluster aerosol and gas concentrations. This indicates that although airmass aging disrupts the short-term linear relationship, the relationship in the average survives. An emission ratio of particles (approx. 100–500 nm diameter) to NOx of approximately 50 cm−3 ppb−1 was estimated in Manchester and Birmingham. Particle mass spectrometry measurements indicated that organic compounds dominated these particles and an emission rate of 0.58 ton km−2 a−1 of organic particulate matter from road transport has been estimated for the Greater Manchester conurbation.

Measurement and Analysis of the Relationship between Ammonia, Acid Gases, and Fine Particles in Eastern North Carolina

An annular denuder system, which consisted of a cyclone separator; two diffusion denuders coated with sodium carbonate and citric acid, respectively; and a filter pack consisting of Teflon and nylon filters in series, was used to measure acid gases, ammonia (NH3), and fine particles in the atmosphere from April 1998 to March 1999 in eastern North Carolina (i.e., an NH3−rich environment). The sodium carbonate denuders yielded average acid gas concentrations of 0.23 μg/m3 hydrochloric acid (standard deviation [SD] ± 0.2 μg/m3); 1.14 μg/m3 nitric acid (SD ± 0.81 μg/m3), and 1.61 μg/m3 sulfuric acid (SD ± 1.58 μg/m3). The citric acid denuders yielded an average concentration of 17.89 μg/m3 NH3 (SD ± 15.03 μg/m3). The filters yielded average fine aerosol concentrations of 1.64 μg/m3 ammonium (NH4 +;SD ± 1.26 μg/m3); 0.26 μg/m3 chloride (SD ± 0.69 μg/m3), 1.92 μg/m3 nitrate (SD ± 1.09 μg/m3), and 3.18 μg/m3 sulfate (SO4 2−; SD ± 3.12 μg/m3). From seasonal variation, the measured particulates (NH4 +,SO4 2−, and nitrate) showed larger peak concentrations during summer, suggesting that the gas-to-particle conversion was efficient during summer. The aerosol fraction in this study area indicated the domination of ammonium sulfate particles because of the local abundance of NH3, and the long-range transport of SO4 2− based on back trajectory analysis. Relative humidity effects on gas-to-particle conversion processes were analyzed by particulate NH4 + concentration originally formed from the neutralization processes with the secondary pollutants in the atmosphere.

Investigating Respiratory Responses to Metalworking Fluid Exposure

In response to worker and union representative concerns, the association between metalworking fluid exposure and respiratory symptoms was investigated in a cross-sectional survey, in a large automotive machining location. A self-administered respiratory symptom-screening questionnaire was sent to 2935 current employees. MWF exposure levels were assigned to respondents on a departmental basis based on average and "peak" area aerosol measurements. MWF exposure, years in the plant, and smoking status were regressed on presence or absence of daily or weekly respiratory symptoms, as well as upper and lower respiratory symptom groupings derived from principal components factor analysis. The response rate was 81 percent. Symptom prevalence was high: 29 percent of subjects reported weekly or daily phlegm; 23 percent, dry cough; 42 percent, runny or plugged nose. Average aerosol concentration in departments with exposure ranged from 0.02 to 0.84 mg/m(3), and peak levels from 0.02 to 2.85 mg/m(3). Average exposures ranging from 0.25 to 0.84 mg/m(3), as compared to exposures in the range of 0.02 to 0.09 mg/m(3), were statistically significantly associated with wheezing, chest tightness, sore throat, and hoarse throat, as well as with the upper respiratory symptom grouping. When peak exposure was included in the regression, it exerted a stronger effect than average exposure level on dry cough, phlegm, wheezing, fever/chills, and hoarse throat, as well as on upper and lower respiratory symptom groupings. These effects were independent of smoking status. Exposure-symptom trends for the average and peak departmental area concentration categories were statistically significant for the upper and lower respiratory symptom groupings and for most individual symptoms. We have observed an association of increasing upper and lower respiratory symptoms with estimated MWF exposure, measured independently, at average departmental aerosol concentrations well below the NIOSH recommended personal exposure level of 0.5 mg/m(3). The results have been used to prioritize exposure reduction efforts in the workplace.

Bulk and size‐segregated aerosol composition observed during INDOEX 1999: Overview of meteorology and continental impacts

Bulk and size‐segregated aerosol samples were collected from the NOAA R/V Ronald H. Brown as it cruised from Cape Town, South Africa, through the Indian Ocean and into the Bay of Bengal and Arabian Sea (February to April 1999; 33°S to 19°N). Throughout the Northern Hemisphere, aerosol loading was greater than in the Southern Hemisphere. Samples collected in air that had passed over India showed evidence of fossil fuel combustion, biomass burning, and eolian material, with elemental carbon (EC) dominating radiation absorption and the following relative contributions to the total mass of aerosol particles: ash 29%, nss‐sulfate 22%, sea salt 15%, nitrate 9%, organic material 8%, ammonium 6%, and EC 5%. Careful examination of the coarse mode revealed substantial concentrations of nitrate, adequate to acidify sea salt aerosols north of the Intertropical Convergence Zone. Air that had passed over Arabia showed little evidence of biomass burning but had more acidity, mineral dust, and higher nitrate to sulfate ratios than air from India. High concentrations of mineral dust played a major role in radiation absorption; mean contributions to aerosol mass in Arabian air were: ash 38%, nss‐sulfate 10%, sea salt 33%, nitrate 5%, organic material 4%, ammonium 1%, and EC 1%. From the ship we measured an average bulk aerosol concentration of 20 μg m−3 in the marine boundary layer of the northern Indian Ocean.

EFFECTS OF NONFIBROUS PARTICLES ON CERAMIC FIBER (RCF1) TOXICITY IN RATS

In previous investigations a reference test sample of prepared ceramic fibers called RCF1 induced lung tumors in a 2-yr inhalation study in rats. It was hypothesized that nonfibrous particles in RCF1 may have played a significant role. The objective of the present study was to compare lung retention and biological effects of another sample of ceramic fibers, called RCF1a, to the original RCF1. The main difference between these 2 samples was the content of nonfibrous particles: 25% of the mass of RCF1 versus 2% for RCF1a. These nonfibrous particles were chemically identical to the fibers. Female Wistar rats were exposed 6 h/day, 5 days/wk for 3 wk to either RCF1a or RCF1 fiber aerosol at a concentration of about 125 fibers (> 20 µm long)/ml. Because of differences in the nonfibrous particle contents, the average gravimetric aerosol concentration differed between the two samples (RCF1, 51.2 mg/m 3; RCF1a, 25.8 mg/m 3) . The post-treatment observation period was 12 mo. Biological effects measured include the clearance function of alveolar macrophages (clearance of fibers and tracer particles), and inflammation and its persistence during the recovery period. Alveolar clearance of tracer particles (46 Sc 2 O 3) was barely retarded after RCF1a exposure (80 days clearance half time compared to 60 days in controls). After RCF1 exposure, however, a severe retardation of clearance was observed (1200 vs. 66 days). In both groups, differential cell counts on pulmonary lavage showed a significant increase of polymorphonuclear leukocytes (PMNs) (about 15%) and lymphocytes 3 days after the end of exposure. The PMN influx persisted longer after exposure to RCF1 than RCF1a. The conclusion of the study is that the particle fraction of RCF1 significantly enhanced any adverse effects. This clearly demonstrates the importance of the physical characteristics of the test material for the degree of toxic effects to be expected. The presence of nonfibrous particulates can enhance the effects on the lung of a mixture of fibrous and nonfibrous particulates following exposure.

Chemical composition of aerosols collected over the tropical North Atlantic Ocean

Ambient aerosol samples were collected over the tropical northern Atlantic Ocean during the month of April 1996 onboard the R/V Seward Johnson. Dichotomous high‐volume collector samples were analyzed for ferrous iron immediately after collection, while trace metals, anions, and cations were determined upon return to the laboratory. Data are analyzed with the aid of enrichment factor, principal component, and weighted multiple linear regression analyses. Average mineral aerosol concentrations amounted to 19.3±16.4 μg m−3 whereby the chemical characteristics and air mass back trajectories indicated the dust to be of a typical shale composition and Saharan origin. Calcite accounted for 3.0 and 7.9% of the mineral aerosol during the first and second halves of the cruise, respectively. Total iron concentrations (averaging 0.84±0.61 μg m−3) are crustally derived, of which 0.51±0.56% is readily released as Fe(II). Eighty‐six percent of this Fe(II) is present in the fine (&lt;3 μm diameter) aerosol fraction and correlates with NSS‐SO42− and oxalate. Approximately 23% of the measured NSS‐SO42− in both size fractions appears to be biogenically derived, and the rest is of anthropogenic nature. Biogenic SO42− /methanesulfonic acid (MSA) ratios could not be easily extracted by employing a multiple linear regression analysis analogous to that of Johansen et al. [1999], possibly due to the varying characteristics of the aerosol chemistry and air temperature during the cruise. Because of the presence of anthropogenic SO42−, the non‐sea‐salt (NSS)‐ SO42−/MSA ratio, 37.4±6.4, is elevated over what would be expected if the NSS ‐ SO42− were purely biogenic. Cl− depletion is seen in all samples and averages 18.3±9.1%. The release of Cl from the aerosol phase appears to occur through acid displacement reactions with primarily HNO3 in the coarse and H2SO4 in the fine fraction.

The vertical structure of aerosol and its relationship to boundary‐layer thermodynamics over the rural UK

AbstractThe vertical structure of aerosol, covering sizes from 0.05‐4 μm radius, was examined under conditions of subsidence during winter and summer over the rural UK. Under well‐mixed boundary layer conditions, dry accumulation mode aerosol was found to be well mixed with height. During the winter campaigns, nocturnal cooling resulted in the development of a stable surface layer, typically 100 m in depth, within which the surface emitted pollutants became trapped leading to concentrations significantly greater than that observed in the mixed boundary layer above it. Under stable boundary‐layer conditions, the aerosol and water vapour vertical profiles exhibited strong negative gradients with height and were indicative of suppressed turbulence associated with stable boundary‐layer conditions. During summer, the boundary layer was normally decoupled and possessed two cloud layers: cumuli forming just below, and penetrating the surface‐layer inversion; and stratocumulus occupying the region under the boundary‐layer capping inversion. Aerosol profiles under decoupled conditions exhibited considerable variability with peak concentrations being observed in the vicinity of cloud edges. Average aerosol concentrations in the main boundary‐layer ranged from 209–651 cm−3 and 0.89–4.3 μm−3 cm−3 for dry number and volume respectively, whilst concentrations and volumetric loadings of 239–2430 cm−3 and 1.1–13.5 μm−3 cm−3 were encountered in surface layers. The majority of the aerosol number and mass concentrations were almost exclusively derived from the size range 0.05‐0.2 μm radius with mode radii often occurring at 0.1 μm or larger. By comparison, free tropospheric aerosol possessed typically an order of magnitude lower concentrations and mass with an associated mode radius of 0.05–0.06 μm or less.

Particulate trace metals above the southern bight of the north sea —I. Analytical procedures and average aerosol concentrations

Heavy metal concentrations in total particulate suspended matter and size fractionated particulate suspended matter above the Southern Bight of the North Sea have been assessed. Most of the samples were collected from a light vessel; the total sampling period covered about 70 days at sea. Stringent precautions were taken during sampling, storage, handling and analysis of the samples. As a conclusions, we found that on a long-term basis the aerosol concentrations above the North Sea have fairly homogeneous composition, but short-term variations probably resulting from point emissions were observed. The cascade impactor results indicated that Pb, Cu, Cd and Zu were carried by submicrometer aerosols, Na, Fe, Mn and Al by supermicrometer aerosols. Most of the samples (70–80%) appeared to be unimodal and log-normally distributed.

Airborne and lidar measurements of aerosol and cloud particles in the troposphere over Alert Canada in April 1986

As a component of the Canadian Arctic Haze Study, held coincident with the second Arctic Gas and Aerosol Sampling Program (AGASP II), vertical profiles of aerosol size distribution (≥0.17 μm), light scattering parameters and cloud particle concentrations were obtained with an instrumented aircraft and ground-based lidar system during April 1986 at Alert. Northwest Territories. Average aerosol number concentrations range from about 200 cm−3 over the Arctic ice cap to about 100 cm−3 at 6 km. The aerosol size spectrum is virtually free of giant or coarse aerosol particles, and does not vary significantly with altitude. Most of the aerosol volume is concentrated in the 0.17–0.50 μm size range, and the aerosol number concentration is found to be a good surrogate for the SO4 = concentration of the Arctic haze aerosol. Comparison of the aircraft and lidar data show that, when iced crystal scattering is excluded, the aerosol light scattering coefficient and the lidar backscattering coefficient are proportional to the Arctic haze aerosol concentration. Ratios of scattering to backscattering, scattering to aerosol number concentration, and backscattering to aerosol number concentration are 15.3 steradians, 1.1×10−13 m2, and 4.8×10−15 m2 sr−1, respectively. Aerosol scattering coefficients calculated from the measured size distributions using Mie scattering agree well with measured values. The calculations indicate the aerosol absorption optical depth over 6 km to range between 0.011 and 0.018. The presence of small numbers of ice crystals (10–20 crystals 1−1 measured) increased light scattering by over a factor of ten.

Retinopathy from inhaling 4,4′-methylenedianiline aerosols

4,4′-Methylenedianiline (MDA) is an important chemical intermediate in the production of isocyanates and polyurethane elastomers and polymers. The health hazards from acute inhalation exposure to the aerosols were evaluated. Guinea pigs of albino and pigmented strains were exposed nose-only to the aerosols of MDA in polyethylene glycol 200 (PEG) solution. The exposure was 4 hr per day, 5 days per week for a total of 10 exposures in 2 weeks. The time-weighted average aerosol concentration was 0.44 ± 0.09 mg/liter and the optical number length mean diameter of the aerosol particle was 2.4μm with σ g of 2.1. During exposures, no overt respiratory distress was observed. Two weeks after the exposures, the guinea pigs were tested for possible dermal sensitization by being challenged with dermal applications of MDA-PEG solutions at concentrations of 0, 2, 20, and 200 mg/ml. Neither dermal irritation nor allergic response was detected under this experimental condition. Thereafter, the animals were tracheostomized for measurements of changes in lung insufflation pressure for detecting possible changes in the distensibility of the lungs from a challenge dose of an aerosol of MDA-PEG at a concentration of 200 mg/ml. No significant changes were observed under this testing condition. Finally, the animals were euthanized for histopathologic examinations of eye, lung, liver, and kidney. The most remarkable finding was the degeneration of the inner and outer segments of the photoreceptor cells and the pigmented epithelial cell layer of the retinas of both albino and pigmented strains of guinea pigs. Since the retinal lesions in both strains of guinea pigs were similar, the retinal changes were, therefore, not related to the affinity between melanin and MDA. Examination of other tissues revealed small pulmonary granulomas or mild granulomatous pneumonitis in most MDA-exposed animals but no remarkable residual lesions in the liver and kidney 2 to 3 weeks postexposure.

Emission of ink aerosol from ink-jet recorders.

As a follow-up of two patients found to be allergic to EKG*ink, a study was made, using spectrophotometric and light microscopic methods, of the factors influencing the emission of ink aerosol from ink-jet recorders used in electrocardiographs. Ink aerosol concentrations were only detectable by spectrophotometry under extreme conditions. However, the light microscopic method was sufficiently sensitive. At the slow paper speeds normally used (10-25 mm/sec) and under normal working conditions, the concentration of ink aerosol near the recorder was less than 0.1 microgram/m3; but aerosol emission increased exponentially with increasing ink pressure, i.e. increasing paper speed. At the highest paper speed studied (200 mm/sec), the aerosol concentration 36 cm from the ink nozzles was about 65 micrograms/m3. An increase in the distance from the ink nozzles to the chart paper resulted in a decrease in ink aerosol emissions. Aerosol dissipation was decreased by local exhaust ventilation of the ink-jet recorder. However, a protective shield designed to catch emitted ink aerosol only reduced the aerosol concentration at the measuring point at slow paper speeds. At higher paper speeds, the concentration increased. The average ink aerosol concentration near modern electrocardiographs is low, but some EKG operations may result in high peak concentrations. The formation of ink aerosol could be considerably reduced by changing the rheologic properties of the ink.