Aerosol Mass Concentration Measurements Research Articles

Long term measurements of aerosol mass concentration with optical particle counters: Discrepancies with plausible reasons

Gravimetry-based direct measurements of mass concentration require offline analysis which is not suited for field campaigns. Hence such campaigns rely on the estimation of mass concentration by indirect methods mostly calibrated in controlled laboratory conditions. Optical particle counter (OPC) employs algorithms converting the measured number concentration to mass concentration using appropriate conversion factors. The accuracy of such conversion has not been validated for widely varying atmospheric conditions. This study compares the mass concentration estimated by OPC with those directly obtained from gravimetry-based instruments for outdoor samples collected in Bathinda City, Punjab, India from January 2022 to November 2023. The difference in the gravimetrically measured and OPC predicted values quantified in terms of ratios (gravimetric to optically estimated mass concentration), came out to be 1.42 ± 0.77, 0.99 ± 0.51, and 1.17 ± 0.58 for PM10, PM2.5 and PM1, respectively. This difference when estimated with the back-up filter of OPC itself (C Factor), was 1.37 ± 0.66. More than half of the samples showed ratios outside the 0.8–1.2 range thus indicating under or over-estimation in the OPC predicted values. The probable role of variation in density, shape, and refractive index of atmospheric aerosol particles towards the observed inaccuracy of estimated mass concentration has been highlighted. In the absence of clear guidelines and protocols, the study suggests ways to improve the accuracy via periodic measurement of the C Factor and/or incorporating calibration factors in such measurements.

Transport of Po Valley aerosol pollution to the northwestern Alps – Part 2: Long-term impact on air quality

Abstract. This work evaluates the impact of trans-regional aerosol transport from the Po basin on particulate matter levels (PM10) and physico-chemical characteristics in the northwestern Alps. To this purpose, we exploited a multi-sensor, multi-platform database over a 3-year period (2015–2017) accompanied by a series of numerical simulations. The experimental setup included operational (24/7) vertically resolved aerosol profiles by an automated lidar ceilometer (ALC), vertically integrated aerosol properties by a Sun/sky photometer, and surface measurements of aerosol mass concentration, size distribution and chemical composition. This experimental set of observations was then complemented by modelling tools, including numerical weather prediction (NWP), trajectory statistical (TSM) and chemical transport (CTM) models, plus positive matrix factorisation (PMF) on both the PM10 chemical speciation analyses and particle size distributions. In a first companion study, we showed and discussed through detailed case studies the 4-D phenomenology of recurrent episodes of aerosol transport from the polluted Po basin to the northwestern Italian Alps. Here we draw more general and statistically significant conclusions on the frequency of occurrence of this phenomenon, and on the quantitative impact of this regular, wind-driven, aerosol-rich “atmospheric tide” on PM10 air-quality levels in this alpine environment. Based on an original ALC-derived classification, we found that an advected aerosol layer is observed at the receptor site (Aosta) in 93 % of days characterized by easterly winds (i.e. from the Po basin) and that the longer the time spent by air masses over the Po plain the higher this probability. Frequency of these advected aerosol layers was found to be rather stable over the seasons with about 50 % of the days affected. Duration of these advection events ranges from few hours up to several days, while aerosol layer thickness ranges from 500 up to 4000 m. Our results confirm this phenomenon to be related to non-local emissions, to act at the regional scale and to largely impact both surface levels and column-integrated aerosol properties. In Aosta, PM10 and aerosol optical depth (AOD) values increase respectively up to factors of 3.5 and 4 in dates under the Po Valley influence. Pollution transport events were also shown to modify the mean chemical composition and typical size of particles in the target region. In fact, increase in secondary species, and mainly nitrate- and sulfate-rich components, were found to be effective proxies of the advections, with the transported aerosol responsible for at least 25 % of the PM10 measured in the urban site of Aosta, and adding up to over 50 µg m−3 during specific episodes, thus exceeding alone the EU established daily limit. From a modelling point of view, our CTM simulations performed over a full year showed that the model is able to reproduce the phenomenon, but markedly underestimates its impact on PM10 levels. As a sensitivity test, we employed the ALC-derived identification of aerosol advections to re-weight the emissions from outside the boundaries of the regional domain in order to match the observed PM10 field. This simplified exercise indicated that an increase in such “external” emissions by a factor of 4 in the model is needed to halve the model PM10 maximum deviations and to significantly reduce the PM10 normalised mean bias forecasts error (from −35 % to 5 %).

Investigation of seasonal variation of compensation parameter and absorption Ångström Exponent of aerosol after loading correction over a remote station in north-east India

One of the extensively used methods for aerosol mass concentration measurement is the optical filter method used in Aethalometer. Due to the aerosol loading and multi scattering effect, there are uncertainties that can lead to underestimation or overestimation of aerosol concentration and measurement of the absorption coefficient. To overcome such uncertainties, a data correction method has been adopted in the present work. During the winter, pre-monsoon and post-monsoon seasons, Aethalometer underestimated black carbon (BC) concentration by 8 ± 1%, 11 ± 1%, and 10.5 ± 0.2%, due to the higher aerosol deposition. While in the monsoon season, underestimation of 5.5 ± 2% is observed because of the presence of bigger scattering nature aerosol. For 70% of days, found a positive correlation between the compensation parameter (k880) and wavelengths, which indicated the dominance of the smaller aerosol particles. While 30% of days have a negative correlation due to the bigger aerosol particle. In the winter, pre-monsoon and monsoon seasons, the absorption coefficient at 370 nm was 86%, 90%, and 93% higher than that of 880 nm due to the higher biomass burning emissions. The absorption Ångström exponent (α370-880) was 1.02 for fossil fuel burning and the corresponding k880 was 0.0037. In the winter and post-monsoon seasons, BC emissions from fossil fuel combustion dominated over the BC emitted by biomass burning emissions with α370-880 < 1.1, whereas α370-880 is found to be more than 1.2 during the pre-monsoon and monsoon seasons due to the higher biomass burning.

Impact of aerosol microphysical properties on mass scattering cross sections

We assessed the sensitivity of simulated mass scattering cross sections (αλsca) of three aerosol species to perturbed particle microphysical properties and derived constraints on these microphysical properties, suitable for the north-western Mediterranean basin, from a comparison between code calculations and observations. In detail, we calculated αλsca of mineral dust, organic carbon and sulfate at three wavelengths in the visible range (λ1=0,450μm; λ2=0,525μm; λ3=0,635μm) with a T-matrix optical code, considering ±20% perturbations on size distribution, refractive index and mass density (respect to reference values mainly taken from the OPAC database), and spheroids with two different axial ratios as shape perturbations (reference shape: sphere). Then, we compared the simulation results with a set of observed αλsca of mineral dust, aged organics and ammonium sulfate sources, available at the same three wavelengths of the code calculations. These observations, provided by the Institute of Environmental Assessment and Water Research (IDAEA-CSIC), have been derived through Multilinear Regression (MLR) analysis from measurements of aerosol mass concentrations and optical properties, collected during a 4-year campaign at the Montseny regional background station (Spain) and representative of the north-western Mediterranean basin. We observed quite different impacts of the microphysical perturbations on αλsca values and spectral dependence for different aerosol species, due mainly to the different size of the particles respect to the visible wavelengths. Moreover, by means of a compatibility test on best fit parameters, we constrained the mineral dust log-normal size distribution to a geometric radius and a standard deviation of rg=3,583·10−1μm and σg=1,600, respectively (effective radius: reff=6,221·10−1μm), the organic carbon log-normal size distribution parameters to rg=2,544·10−2μm and σg=1,760 (reff=5,656·10−2μm), the organic carbon real refractive index to nR=(1,576;1,576;1,576) at (λ1;λ2;λ3), the sulfate log-normal size distribution parameters to rg=8,340·10−2μm and σg=1,624 (reff=1,501·10−1μm) and the sulfate real refractive index to nR=(1,547;1,545;1,543) at (λ1;λ2;λ3), in the north-western Mediterranean basin. Regarding the other perturbed microphysical properties, we found the reference prescriptions to be suitable for this geographical region, according to the same analysis procedure.

Optical properties of mixed aerosol layers over Japan derived with multi-wavelength Mie–Raman lidar system

Mixing state of aerosols and optical properties including lidar ratio, particle depolarization ratio, and Ångström exponent were investigated at Fukuoka in western Japan using a multi-wavelength Mie–Raman lidar (MMRL), various aerosol mass-concentration measurements, and a polarization optical particle counter during Winter–Spring 2015. Aerosol extinction coefficient, backscatter coefficient, and depolarization at 355 and 532nm and attenuated backscatter coefficient at 1064nm are obtained from the MMRL measurements. Ten aerosol episodes were classified into three categories (air pollution, mineral dust, and marine aerosol) based on aerosol mass-concentration measurements in the fine-mode (particle diameter Dp<2.5μm) and coarse-mode (2.5μm<Dp<10μm). The mean lidar ratio for air pollution was 57±4sr at 355nm and 53±8sr at 532nm with Ångström exponent of 1.4±0.5. For mineral dust, a slightly high averaged lidar ratio (50±7sr at 355nm and 54±9sr at 532nm) was obtained with relatively high Ångström exponent of 0.8±0.3 owing to contributions from fine-mode particles (PMf). The mean particle depolarization ratios of 13±8% at 355nm and 16±6% at 532nm also suggest mixing of mineral dust and anthropogenic fine-mode aerosols. The lowest lidar ratio was obtained for marine case. Classification of aerosol types using the lidar ratio and particle depolarization ratio was conducted based on the results obtained in this study. The classified aerosol types almost corresponded to aerosol category obtained by previous studies. We found no remarkable correlation between the fraction of black carbon and the lidar ratio: this might be due to the complexity of the mixing state among various aerosols. The obtained lidar ratio was rather correlated with the ratio of PMf to PM10, representing the mixing state of fine- and coarse-mode particles.

A new method for estimating aerosol mass flux in the urban surface layer using LAS technology

Abstract. Atmospheric aerosol greatly influences human health and the natural environment, as well as the weather and climate system. Therefore, atmospheric aerosol has attracted significant attention from society. Despite consistent research efforts, there are still uncertainties in understanding its effects due to poor knowledge about aerosol vertical transport caused by the limited measurement capabilities of aerosol mass vertical transport flux. In this paper, a new method for measuring atmospheric aerosol vertical transport flux is developed based on the similarity theory of surface layer, the theory of light propagation in a turbulent atmosphere, and the observations and studies of the atmospheric equivalent refractive index (AERI). The results show that aerosol mass flux can be linked to the real and imaginary parts of the atmospheric equivalent refractive index structure parameter (AERISP) and the ratio of aerosol mass concentration to the imaginary part of the AERI. The real and imaginary parts of the AERISP can be measured based on the light-propagation theory. The ratio of the aerosol mass concentration to the imaginary part of the AERI can be measured based on the measurements of aerosol mass concentration and visibility. The observational results show that aerosol vertical transport flux varies diurnally and is related to the aerosol spatial distribution. The maximum aerosol flux during the experimental period in Hefei City was 0.017 mg m−2 s−1, and the mean value was 0.004 mg m−2 s−1. The new method offers an effective way to study aerosol vertical transport in complex environments.

Research on the fractal model and calibration of the aerosol mass concentration measurement based on the particle group light scattering

In order to improve the inversion precision of aerosol mass concentrations based on the particle group light scattering method, the concept that particles through a laser beam are equivalent to an aggregate is proposed. A fractal model for aerosol mass concentration using the signal amplitude distribution of aggregates is presented, and then the subsection calibration method is given. The experimental results show that the mass concentrations inversed by this model agree well with those measured by the norm-referenced instrument. The average relative errors of the two experiments are 5.6% and 6.0%, respectively, which are less than those obtained by the conventional inversion model.

Intercomparison between a single particle soot photometer and evolved gas analysis in an industrial area in Japan: Implications for the consistency of soot aerosol mass concentration measurements

Abstract Mass concentrations of soot (typically comprising black and elemental carbon; BC and EC, respectively) aerosols, were measured at Yokosuka city, an industrial region in Japan in the early summer of 2014. The results of laser–induced incandescence (LII) and evolved gas analysis (EGA) techniques were compared using a single particle soot photometer (SP2) and semi-continuous elemental/organic carbon analyzer (EC/OC analyzer), respectively. We revisited the procedure of SP2 calibration with a focus on investigating the relationship between LII intensity ( S LII ) and refractory BC (rBC) mass per particle ( m PP ) for some BC-proxies in the laboratory, as well as for ambient rBC particles in order to discuss the uncertainty of the SP2. It was found that the m PP – S LII for the fullerene soot and carbon black particles agreed well within 3% and 10%, respectively, with that for ambient rBC particles. This is the first time to suggest the use of carbon black as a reference material. We also found that the m PP – S LII for the aqueous deflocculated Acheson graphite particles with the correction factor given by Baumgardner et al. (2012) was still biased by around +20% to that for ambient rBC particles. EC quantified by the semi-continuous EC/OC analyzer using a thermal-protocol similar to that of Interagency Monitoring of Protected Visual Environments (IMPROVE–like), systematically showed higher concentrations than rBC measured by the SP2. The uncertainties related to SP2 cannot fully account for this difference. This result was likely caused by the contribution of charred organic materials to EC, which can be affected significantly by thermal-protocols for the EGA. The consistency and differences between rBC and EC are discussed with regard to comparing their respective mass concentrations.

Study of 7Be and 210Pb as radiotracers of African intrusions in Malaga (Spain)

The relationship between the particulate matter in the atmosphere of Malaga and the origin of air masses with special attention to African intrusions was analyzed. The concentrations of PM10 and the activities of some radionuclides (7Be and 210Pb) as tracers of these intrusions are discussed. The origin of these radiotracers is completely different. 210Pb is a good tracer of air masses traveling close to the ground and come from inland areas. On the other hand, the production of 7Be is very low in the vicinity of the Earth's surface, and increases with altitude, making it a great tracer of stratospheric air masses in the troposphere.Studies of radionuclide activities in aerosol particles provide a means for evaluating the integrated effects of transport and meteorology on the atmospheric loadings of substances with different sources. Measurements of aerosol mass concentration and specific activities of 7Be and 210Pb in aerosols at Malaga (36° 43′ 40″ N; 4° 28′ 8″ W) for the period 2009–2011 were used to obtain the relationships between radionuclide activities and airflow patterns by comparing the data grouped by air mass trajectory. The average concentration values of 7Be and 210Pb over the 3-year period have been found to be 5.05 and 0.55 mBq m−3, respectively, with mean aerosol mass concentration of 53.6 μg m−3. Taking into account the outbreaks of the daily values limits of PM10 in the study period (2009–2011), the origin of air masses is studied to explain three different situations of both radionuclides 7Be and 210Pb: 1) high concentrations of 7Be and low concentrations of 210Pb; 2) high concentrations of 210Pb and low concentrations of 7Be and 3) high concentrations of 7Be and 210Pb.

Long term black carbon measurements in the southwestern Iberia Peninsula

Black carbon mass concentration (BCPM10) measurements carried out at Évora, Portugal, between 2007 and 2009, were analyzed and interpreted at different timescales. Additional measurements of aerosol mass concentration (MPM10) were included and the black carbon to total mass fraction (BC mass fraction) was derived when measurements of both quantities were coincident. BCPM10 values were found to vary between 0.3 and 5 μg m−3, mainly in the range of 0.5–2 μg m−3. A clear and consistent seasonal behavior was found; an increase by a factor of two in the average BCPM10 values was observed from summer (0.9 μg m−3) to winter (1.8 μg m−3) which is reflected in the BC mass fraction, amplified from about 4 to 10%. Comparison of the average BCPM10 mass concentrations on week days and week ends indicate that local traffic emissions strongly influence the observed average diurnal patterns. Other factors, such as wood burning for heating, lower boundary layer height and more frequent winter-time temperature inversions, also likely influence the observed BCPM10 but were not directly studied here. When different air mass types are considered then black carbon levels show a much lower variation than PM10 mass concentrations, stressing the relevance of local emissions in the BCPM10 levels. BCPM10 values under continental or maritime influence only differ by a factor of approximately 1.4 only, much lower than the factor of 10 reported for a coastal rural site in Portugal.

Workplace aerosol mass concentration measurement using optical particle counters

Direct-reading aerosol measurement usually uses the optical properties of airborne particles to detect and measure particle concentration. In the case of occupational hygiene, mass concentration measurement is often required. Two aerosol monitoring methods are based on the principle of light scattering: optical particle counting (OPC) and photometry. The former analyses the light scattered by a single particle, the latter by a cloud of particles. Both methods need calibration to transform the quantity of scattered light detected into particle concentration. Photometers are simpler to use and can be directly calibrated to measure mass concentration. However, their response varies not only with aerosol concentration but also with particle size distribution, which frequently contributes to biased measurement. Optical particle counters directly measure the particle number concentration and particle size that allows assessment of the particle mass provided the particles are spherical and of known density. An integrating algorithm is used to calculate the mass concentration of any conventional health-related aerosol fraction. The concentrations calculated thus have been compared with simultaneous measurements by conventional gravimetric sampling to check the possibility of field OPC calibration with real workplace aerosols with a view to further monitoring particle mass concentration. Aerosol concentrations were measured in the food industry using the OPC GRIMM® 1.108 and the CIP 10-Inhalable and CIP 10-Respirable (ARELCO®) aerosol samplers while meat sausages were being brushed and coated with calcium carbonate. Previously, the original OPC inlet had been adapted to sample inhalable aerosol. A mixed aerosol of calcium carbonate and fungi spores was present in the workplace. The OPC particle-size distribution and an estimated average particle density of both aerosol components were used to calculate the mass concentration. The inhalable and respirable aerosol fractions calculated from the OPC data are closely correlated with the results of the particle size-selective sampling using the CIP 10. Furthermore, the OPC data allow calculation of the thoracic fraction of workplace aerosol (not measured by sampling), which is interesting in the presence of allergenic particles like fungi spores. The results also show that the modified COP inlet adequately samples inhalable aerosol in the range of workplace particle-size distribution.

Air mass origin and its influence on radionuclide activities ( 7Be and 210Pb) in aerosol particles at a coastal site in the western Mediterranean

Studies of radionuclide activities in aerosol particles provide a means for evaluating the integrated effects of transport and meteorology on the atmospheric loadings of substances with different sources. Measurements of aerosol mass concentration and specific activities of 7Be and 210Pb in aerosols at Málaga (36° 43′ 40″ N; 4° 28′ 8″ W) for the period 2000–2006 were used to obtain the relationships between radionuclide activities and airflow patterns by comparing the data grouped by air mass trajectory clusters. The average concentration values of 7Be and 210Pb over the 7 year period have been found to be 4.6 and 0.58 mBq m −3, respectively, with mean aerosol mass concentration of 53.6 μg m −3. The identified air flow types arriving at Málaga reflect the transitional location of the Iberian Peninsula and show significant differences in radionuclide activities. Air concentrations of both nuclides and the aerosol mass concentration are controlled predominantly by the synoptic scenarios leading to the entrance of dust-laden continental flows from northern Africa and the arrival of polar maritime air masses, as implied by the strong correlations found between the monthly frequencies of the different air masses and the specific activities of both radionuclides. Correlations between activity concentrations and precipitation are significant though lower than with air masses.

Characterising aerosol transport into the Canadian High Arctic using aerosol mass spectrometry and Lagrangian modelling

Abstract. We report the analysis of measurements made using an aerosol mass spectrometer (AMS; Aerodyne Research Inc.) that was installed in the Polar Environment Atmospheric Research Laboratory (PEARL) in summer 2006. PEARL is located in the Canadian high Arctic at 610 m above sea level on Ellesmere Island (80° N 86° W). PEARL is unique for its remote location in the Arctic and because most of the time it is situated within the free troposphere. It is, therefore, well suited as a receptor site to study the long-range tropospheric transport of pollutants into the Arctic. Some information about the successful year-round operation of an AMS at a high Arctic site such as PEARL will be reported here, together with design considerations for reliable sampling under harsh low-temperature conditions. Computational fluid dynamics calculations were made to ensure that sample integrity was maintained while sampling air at temperatures that average −40 °C in the winter and can be as low as −55 °C. Selected AMS measurements of aerosol mass concentration, size and chemical composition recorded during the months of August, September and October 2006 will be reported. The air temperature was raised to about 20 °C during sampling, but the short residence time in the inlet system (~25 s) ensured that less than 10% of semivolatiles such as ammonium nitrate were lost. During this period, sulfate was, at most times, the predominant aerosol component with on average 0.115 μg m−3 (detection limit 0.003 μg m−3). The second most abundant component was undifferentiated organic aerosol, with on average 0.11 μg m−3 (detection limit 0.04 μg m−3). The nitrate component, which averaged 0.007 μg m−3, was above its detection limit (0.002 μg m−3), whereas the ammonium ion had an apparent average concentration of 0.02 μg m−3, which was approximately equal to its detection limit. A few episodes, having increased mass concentrations and lasting from several hours to several days, are apparent in the data. These were investigated further using a statistical analysis to determine their common characteristics. High correlations among some of the components arriving during the short-term episodes provide evidence for common sources. Lagrangian methods were also used to identify the source regions for some of the episodes. In all cases, these coincided with the arrival of air that had contacted the surface at latitudes below about 60° N. Most of these lower-latitude footprints were on land, but sulfate emissions from shipping in the Atlantic were also detected. The Lagrangian results demonstrate that there is direct transport of polluted air into the high Arctic (up to 80° N) from latitudes down to 40° N on a time scale of 2–3 weeks. The polluted air originates in a wide variety of industrial, resource extraction and petroleum-related activity as well as from large population centres.

Chemical apportionment of southern African aerosol mass and optical depth

Abstract. This study characterizes the aerosol over extratropical and tropical southern Africa during the biomass burning season by presenting an aerosol mass apportionment and aerosol optical properties. Carbonaceous aerosol species account for 54% and 83% of the extratropical and tropical aerosol mass, respectively, which is consistent with the fact that the major source of particulate matter in southern Africa is biomass burning. This mass apportionment implies that carbonaceous species in the form of organic carbon (OC) and black carbon (BC) play a critical role in the aerosol optical properties. By combining the in situ measurements of aerosol mass concentrations with concurrent measurements of aerosol optical properties at a wavelength of 550 nm, it is shown that 80–90% of the aerosol scattering is due to carbonaceous aerosol, and the derived mass scattering cross sections (MSC) for OC and BC are 3.9±0.6 m2/g and 1.6±0.2 m2/g, respectively. Derived values of mass absorption cross sections (MAC) for OC and BC are 0.7±0.6 m2/g and 8.2±1.1 m2/g, respectively. The values of MAC imply that ~26% of the aerosol absorption in southern Africa is due to OC, with the remainder due to BC. The results in this study provide important constraints for aerosol properties in a region dominated by biomass burning and should be integrated into climate models to improve aerosol simulations.

INVESTIGATION OF AEROSOL NUMBER CONCENTRATION IN JONAVA TOWN/AEROZOLIŲ SKAITINĖS KONCENTRACIJOS TYRIMAI JONAVOJE/ИССЛЕДОВАНИЕ ЧИСЛОВОЙ КОНЦЕНТРАЦИИ АЭРОЗОЛЯ В ГОРОДЕ ЙОНАВЕ

Abstract Though some authors declare that aerosol number concentration might be a better indicator of health effects of the particulates than the mass method, there is lack of aerosol number investigation studies. Most of air quality studies so far have been based on aerosol mass concentration measurements. Lithuanian National Air Quality Monitoring Network does not carry out aerosol number concentration measurements. Nonetheless, detailed particulate matter mass concentration investigation studies are made periodically in the biggest Lithuanian cities by various scientific organizations. Jonava seems to be overpassed even there. This is the reason for choosing the investigation object. In Jonava town persistent measurements of aerosol number concentration were performed since 21 till 29 of November in the year 2006. The pollutants were measured with an optical particle counter AZ‐5. The fluctuations of 24 hours, diurnal aerosol number concentration were analysed. The weather was favorable for pollutant a...

Size segregated aerosol mass concentration measurements over the Arabian Sea during ICARB

Mass concentration and mass size distribution of total (composite) aerosols near the surface are essential inputs needed in developing aerosol models for radiative forcing estimation as well as to infer the environment and air quality. Using extensive measurements onboard the oceanographic research vessel, Sagar Kanya, during its cruise SK223B in the second phase of the ocean segment of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB), the spatial distribution of the mass concentration and mass size distribution of near-surface aerosols are examined for the first time over the entire Arabian Sea, going as far as 58°E and 22°N, within a span of 26 days. In general, the mass concentrations (MT ) were found to be low with the mean value for the entire Arabian Sea being 16.7 ± 7 μg m−3; almost 1/2 of the values reported in some of the earlier campaigns. Coarse mode aerosols contributed, on an average, 58% to the total mass, even though at a few pockets accumulation mode contribution dominated. Spatially, significant variations were observed over central and northern Arabian Sea as well as close to the west coast of India. In central Arabian Sea, even though the MT was quite low, contribution ofs accumulation aerosols to the total mass concentration was greater than 50%. Effective radius, a parameter important in determining scattering properties of aerosol size distribution, varied between 0.07 and 0.4 μm with a mean value of 0.2 μm. Number size distributions, deduced from the mass size distributions, were approximated to inverse power-law form and the size indices (ν) were estimated. It was found to vary in the range 3.9 to 4.2 with a mean value of 4.0 for the entire oceanic region. Extinction coefficients, estimated using the number-size distributions, were well-correlated with the accumulation mode mass concentration with a correlation coefficient of 0.82.

In situ measurements of aerosol mass concentration and radiative properties in Xianghe, southeast of Beijing

As a part of the EAST‐AIRE study, Nuclepore filters were collected in two size ranges (coarse, 2.5 μm &lt; d &lt; 10 μm, and fine, d &lt; 2.5 μm) from January to May 2005 in Xianghe, about 70 km southeast of Beijing, and analyzed for aerosol mass concentration, spectral absorption efficiency and absorption coefficient. Twelve‐hour aerosol mass concentration measurements showed an average concentration of 120 μg/m3 in the coarse mode and an average concentration of 25 μg/m3 in the fine mode. To determine how representative ground‐based measurements are of the total column, the mass concentration data was compared with AERONET AOT at 500 nm and AERONET size distribution data. The vertical distribution of the aerosols were studied with a micropulse lidar and in the cases where the vertical column was found to be fairly homogenous, the comparisons of the filter results with AERONET agreed favorably, while in the cases of inhomogeneity, the comparisons have larger disagreement. For fine mode aerosols, the average spectral absorption efficiency equates well to a λ−1 model, while the coarse mode shows a much flatter spectral dependence, consistent with large particle models. The coarse mode absorption efficiency was compatible with that of the fine mode in the NIR region, indicating the much stronger absorption of the coarse mode due to its composition and sizable mass. Single scattering albedo results are presented from a combination between absorption coefficients derived from the filter measurements, from a PSAP and from a three‐wavelength Nephelometer.

Correction in aerosol mass concentration measurements with humidity difference between ambient and instrumental conditions

The influence of humidity is considered on the concentration of the suspended particulate matter (SPM) measured with a β-ray counter. The humidity condition inside a small observatory where the counter is located is, in general, different from the ambient condition outside the observatory. From the measured values, the ambient SPM concentration is derived considering the hygroscopic effect of common aerosol species of sea salt (SS), (NH 4) 2SO 4, NH 4NO 3 and NaNO 3. In a case study conducted during September 2005, temperature and humidity were measured both inside and outside the observatory. The average value of the relative humidity is 48% for inside and 78% for outside, resulting in approximately 53% larger SPM mass concentration after the correction. Accordingly, the value of mass extinction efficiency, which is given by the ratio between the optically measured extinction coefficient and the mass concentration, becomes lower after the correction.

Aircraft-based operation of an aerosol mass spectrometer: Measurements of tropospheric aerosol composition

The Aerodyne quadrupole aerosol mass spectrometer was deployed on the Falcon twin jet research aircraft operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). This was the first deployment of an AMS in a jet aircraft. Aerosol mass concentration measurements in the troposphere up to altitudes of about 11 km were performed within two measurement flights on 12 and 14 May 2003 over southern Germany. Background aerosol data were gained up to 6 km, while aircraft exhaust aerosol was be sampled at higher altitudes on 14 May, indicating the presence of sulfuric acid and unburned hydrocarbons in the exhaust particles. The boundary layer aerosol on 12 May was found to be composed of 49% organics, 12% sulfate, 15% ammonium, and 24% nitrate by mass. The upper edge of the boundary layer was marked by a sharp decrease of nitrate and ammonium at an altitude of 3 km, while sulfate and organics decreased to a much lesser degree. On 14 May, the boundary layer aerosol was composed of 23% organics, 20% sulfate, 24% ammonium, and 33% nitrate by mass, and the boundary layer reached up to about 5000 m and had no sharp upper edge. The size distributions indicated internal mixtures of ammonium sulfate and –nitrate in the boundary layer, while the organics were externally mixed. Additionally, a smaller mode consisting only of ammonium sulfate, was detected. This bimodal structure of ammonium sulfate was also detected above the boundary layer in 6 km altitude on 14 May.

Development of a continuous aerosol mass concentration measurement device.

A dynamic aerosol mass concentration measurement device has been developed for personal sampling. Its principle consists in sampling the aerosol on a filter and monitoring the change of pressure drop over time (Delta P). Ensuring that the linearity of the Delta P = f(mass of particles per unit area of filter) relationship has been well established, the change of concentration can be deduced. The response of the system was validated in the laboratory with a 3.5 microm alumina aerosol (mass median diameter) generated inside a 1-m(3) ventilated enclosure. As the theory predicted that the mass sensitivity of the system would vary inversely with the square of the particle diameter, only sufficiently fine aerosols were able to be measured. The system was tested in the field in a mechanical workshop in the vicinity of an arc-welding station. The aerosol produced by welding is indeed particularly well-adapted due to the sub-micronic size of the particles. The device developed, despite this limitation, has numerous advantages over other techniques: robustness, compactness, reliability of calibration, and ease of use.