Estimating the near-surface daily fine aerosol load using hourly Radon-222 observations
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We investigate the extent to which hourly radon observations can be used to estimate daily PM2.5 loading near the ground. We formulate, test and apply a model that expresses the mean daily PM2.5 load as a linear combination of observed radon concentrations and differences on a given day. The model was developed using two consecutive years of observations (2007–2008) at four sites near Sydney, Australia, instrumented with aerosol samplers and radon detectors. Model performance was subsequently evaluated against observations in 2009. After successfully reproducing mean daily radon concentrations (r2≥0.98), we used the model to estimate daily PM2.5 mass, as well as that of selected elements (Si, K, Fe, Zn, H, S and Black Carbon). When parameterizing the model for elemental mass estimates the highest r2 values were generally obtained for H, BC, K and Si. Separating results by season, the r2 values for K and BC were higher in winter for all sites, a period of time where higher concentrations of these elements are seen and a rapid estimation tool would be of particular benefit. The best overall results were obtained in winter for H and BC [r2 = 0.50, 0.68, 0.70, 0.63 (H) and 0.57, 0.57, 0.78, 0.44 (BC)], respectively for Warrawong, Lucas Heights, Richmond and Muswellbrook. Evaluation of model PM2.5 estimates was most successful for days with typical aerosol loads; loads were usually underestimated for, the less frequent, high–to–extreme pollution days. The best elemental results were obtained for BC at Richmond in winter (r2 = 0.68). However, for Warrawong and Lucas Heights r2 values increased from 0.26 to 0.60, and from 0.33 to 0.73, respectively, when several particularly high concentration events were excluded from the analysis. The model performed best at Richmond, an inland site with relatively flat terrain. However, model parameters need to be evaluated for each site.Keywords:
Mass concentration (chemistry)
The mass concentrations of both vapor and aerosol phases of 4,4′ -bipyridyl were determined by a glass fiber filter and an XAD-2 tube in a paraquat factory. The size distributions of 4,4′ -bipyridyl aerosols and particles <10 µm were measured by a six-stage cascade impactor. The mass concentrations of 4,4′ -bipyridyl aerosols were in the range of 81.9 to 159.9 mg/m3 with an average 4,4′ -bipyridyl vapor mass concentration of 3.1 mg/m3 at the top of the open tank. On the average, the mass ratio of vapor phase to aerosol phase of 4,4′ -bipyridyl was 0.025. Therefore, the aerosol phase is the major form of 4,4′ -bipyridyl exposure to the workers in this environment. From the 4,4′ -bipyridyl concentrations measured by the sampling systems of an XAD-2 tube alone and a filter followed by an XAD-2 tube, the 4,4′ -bipyridyl aerosol collection efficiency of the XAD-2 tube was found to be approximately 50%. The average mass concentrations of less than 10 µm aerosols and 4,4′ -bipyridyl aerosol in the occupational environment were 0.42 mg/m3 and 1.26 µg/m3, respectively. The mass median aerodynamic diameter (geometric standard deviation) of particles <10 µm and 4,4′ -bipyridyl aerosol are 3.50 µm (2.35) and 3.47 µm (2.58), respectively. The major mass fraction of 4,4′ -bipyridyl aerosol occurred in the 3.3–5.8 µm she range. The enclosure efficiencies of a hood cover attached to a suction tube were found to be 88% and 82% for both aerosol and vapor phases of 4,4′ -bipyridyl, respectively. It is suggested that the heterogeneous nucleation of 4,4′ -bipyridyl and water vapor from the open tanks with subsequent coagulation is the major mechanism of aerosol formation. We conclude that both 4,4′ -bipyridyl aerosol and vapor concentration should be determined for the exposure assessment of the paraquat manufacturer in this workplace.
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Sulfate aerosol
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Abstract. Atmospheric aerosol has a great influence on human health and the natural environment as well as the weather and climate system. Therefore, atmospheric aerosol has attracted significant attention from the society as a whole. Despite consistent research efforts, there are still uncertainties in our understanding of its effects due to poor knowledge of aerosol vertical transport caused by our limited measurement capability 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 theoretical 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 atmospheric equivalent refractive index (AERI). The real and imaginary parts of AERISP can be measured based on the light propagation theory. The ratio of aerosol mass concentration to the imaginary part of 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 mgm−2s−1, and the mean value was 0.004 mgm−2s−1. The new method offers an effective way to study aerosol vertical transport over complex environments.
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Mass flux
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Abstract. A physicochemical characterization, including aerosol number size distribution, chemical composition and mass concentrations, of the urban fine aerosol captured in MILAN, BARCELONA and LONDON is presented in this article. The objective is to obtain a comprehensive picture of the microphysical processes involved in aerosol dynamics during the: 1) regular evolution of the urban aerosol (daily, weekly and seasonal basis) and in the day-to-day variations (from clean-air to pollution-events), and 2) the link between "aerosol chemistry and mass concentrations" with the "number size distribution". The mass concentrations of the fine PM2.5 aerosol exhibit a high correlation with the number concentration of >100 nm particles N>100 (nm) ("accumulation mode particles") which only account for <20% of the total number concentration N of fine aerosols; but do not correlate with the number of <100 nm particles ("ultrafine particles"), which accounts for >80% of fine particles number concentration. Organic matter and black-carbon are the only aerosol components showing a significant correlation with the ultrafine particles, attributed to vehicles exhausts emissions; whereas ammonium-nitrate, ammonium-sulphate and also organic matter and black-carbon correlate with N>100 (nm) and attributed to condensation mechanisms, other particle growth processes and some primary emissions. Time series of the aerosol DpN diameter (dN/dlogD mode), mass PM2.5 concentrations and number N>100 (nm) concentrations exhibit correlated day-to-day variations, which point to a significant involvement of condensation of semi-volatile compounds during urban pollution events. This agrees with the observation that ammonium-nitrate is the component exhibiting the highest increases from mid-to-high pollution episodes, when the highest DpN increases are observed. The results indicates that "fine PM2.5 particles urban pollution events" tend to occur when condensation processes have made particles grow large enough to produce significant number concentrations of N>100 (nm) ("accumulation mode particles"). In contrast, because the low contribution of ultrafine particles to the fine aerosol mass concentrations, high "ultrafine particles N<100(nm) events" frequently occurs under low PM2.5 conditions. The results of this study demonstrate that vehicles exhausts emissions are strongly involved in this ultrafine particles aerosol pollution.
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Ultrafine particle
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Abstract. A physicochemical characterization of the urban fine aerosol (aerosol number size distribution, chemical composition and mass concentrations) in Milan, Barcelona and London is presented in this article. The objective is to obtain a comprehensive picture on the involvement of the microphysical processes of the aerosol dynamic in the: 1) regular evolution of the urban aerosol (daily, weekly and seasonal basis) and in the day-to-day variations (from clean-air to pollution-events), and 2) link between "aerosol chemistry and mass concentrations" with the "number size distribution". The mass concentrations of the fine PM2.5 aerosol exhibit a high correlation with the number concentration of particles >100 nm (which only accounts for <20% of the total number concentration N of fine aerosols) and do not correlate with the number of particles <100 nm ("ultrafine particles", which accounts for >80% of fine particles). Organic matter (OM) and black-carbon (BC) are the only aerosol components showing a significant correlation with ultrafine particles (attributed to vehicles emissions), whereas ammonium-nitrate, ammonium-sulphate and also OM and BC correlate with N>100(nm) (attributed to gas-to-particle transformation mechanisms and some primary emissions). Time series of the aerosol DpN diameter (dN/dlogD mode), mass PM2.5 concentrations and number N>100(nm) concentrations, exhibit correlated day-to-day variations which point to a significant involvement of condensation of semi-volatile compounds during urban pollution events. This agrees with the fact that ammonium-nitrate is the component exhibiting the highest increases from mid-to-high pollution episodes, when the highest DpN increases are observed. The results indicates that "fine PM2.5 particles urban pollution events" tend to occur when condensation processes have made particles grow enough to produce significant concentrations of N>100(nm). In contrast, because the low contribution of ultrafine particles to the fine aerosol mass concentrations, high "ultrafine particles N<100(nm) events" frequently occurs under low PM2.5 conditions. The data of this study point that vehicles emissions are strongly involved in this ultrafine particles aerosol pollution (for example, the "morning-rush-hours to nocturnal-background" concentrations ratio is 1.5–2.5 for "particles 10–100 nm" and <1.5 for both "particle >100 nm and PM2.5").
Ultrafine particle
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Ammonium nitrate
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Based on aerosol mass concentration and number concentration data and meteorological data at different heights and backward trajectory analysis,the influence of a sand-dust weather process from April 30 to May 1 in 2011 on aerosol concentration in Tianjin were analyzed.The results indicated as follows.In the mist process before sand-dust weather,PM1 accounted for about 96% of aerosol mass concentration and 99.9% of aerosol number concentration;PM1-2.5,PM2.5-10 and PM10-100 accounted for about 6.5%,2.5% and 0.1% respectively of total aerosol number concentration in the first floating dust process,11.3%,2.6% and 0.01% respectively in the second floating dust process;the mass concentration and number concentration of fine aerosol under two floating dust processes were obviously different because of the increase of the ratio of fine aerosol,which resulted in change of aerosol property.
Mass concentration (chemistry)
Mist
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The correlations of seasonal arrays of mass concentrations of submicron aerosol and black carbon (BC, soot) measured at the Aerosol station of the IAO SB RAS (suburban area of Tomsk) and in the background area ("Fonovaya" observatory) in 2014-2020 are analyzed. Linear dependence is revealed between the logarithms of the corresponding aerosol characteristics at two stations for seasonal data arrays at each hour of a day. The background values of the mass concentrations of submicron aerosol and soot are reconstructed on the basis of the analysis, and the errors in reconstructing are estimated. The possibility is shown of the use of the obtained empirical coefficients for reconstruction of the aerosol characteristics recorded at the "Fonovaya" observatory.
Mass concentration (chemistry)
Seasonality
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