Size-resolved Aerosol Concentrations Research Articles

Aerosol deposition to the boreal forest in the vicinity of the Alberta Oil Sands

Abstract. Measurements of size-resolved aerosol concentration and fluxes were made in a forest in the Athabasca Oil Sands Region (AOSR) of Alberta, Canada, in August 2021 with the aim of investigating (a) particle size distributions from different sources, (b) size-resolved particle deposition velocities, and (c) the rate of vertical mixing in the canopy. Particle size distributions were attributed to different sources determined by wind direction. Air mixed with smokestack plumes from oil sands processing facilities had higher number concentrations with peak number at diameters near 70 nm. Aerosols from the direction of open-pit mine faces showed number concentration peaks near 150 nm and volume distribution peaks near 250 nm (with secondary peaks near 600 nm). Size-resolved deposition fluxes were calculated which show good agreement with previous measurements and a recent parameterization. There is a minimum deposition velocity of vd=0.02 cm s−1 for particles of 80 nm diameter; however, there is a large amount of variation in the measurements, and this value is not significantly different from zero in the 68 % confidence interval. Finally, gradient measurements of aerosol particles (with diameters <1 µm) demonstrated nighttime decoupling of air within and above the forest canopy, with median lag times at night of up to 40 min and lag times between 2 and 5 min during the day. Aerosol mass fluxes (diameters <1 µm) determined using flux–gradient methods (with different diffusion parameterizations) underestimate the flux magnitude relative to eddy covariance flux measurements when averaged over the nearly 1-month measurement period. However, there is significant uncertainty in the averages determined using the flux–gradient method.

Seasonal variation of size-resolved aerosol fluxes in a Peri-urban deciduous broadleaved forest

Eddy covariance measurements of aerosol fluxes were performed above an oak-hornbeam forest in the Po Plain (Northern Italy), from February to May and from September to December 2019. Measurements aimed at assessing the influence of forest phenology and leaf presence/absence on the seasonal evolution of size-segregated aerosol fluxes. The size-resolved aerosol concentration in the range 0.006-10 μm was sampled with a 14-stage impactor (ELPI+, Dekati, FI), and the filters exposed in May were subjected to chemical analysis. Over the whole sampling period, the forest removed from the atmosphere an average of 3.12 mg of aerosol m−2 d−1. The direction and the intensity of the aerosol fluxes were not constant through the year, as a strong seasonal and size-dependent variability emerged. In particular, leaf-presence drove a net deposition of the accumulation mode aerosol (100 nm< particle diameter Dp<1000 nm) and an emission of the Aitken (10 nm< Dp<100 nm) and coarse mode (Dp>1000 nm) aerosols. On the contrary, in absence of leaves all the sub-micrometer aerosol size-classes showed net daily upward fluxes, while coarse mode aerosol fluxes were prevalently downward. Monthly averages of deposition velocities of Aitken and accumulation mode aerosols correlated with the Leaf Area Index (LAI) seasonal trend, thus indicating an important role of the amount of the leaf surface area on the deposition and emission of these size-classes. Furthermore, an influence of the stomatic activity was suggested for the Aitken mode aerosol, since its deposition velocity followed the same diel course of the stomatal conductance to water. The analysis of the influence of meteorological parameters on aerosol deposition velocities highlighted that dynamic and convective turbulence (described by friction velocity, u* and Deardorff velocity, w*) enhanced the vertical aerosol exchanges, both upward and downward, while the approaching of condensing conditions reduced the flux intensities.

Lower tropospheric distributions of O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; and aerosol over Raoyang, a rural site in the North China Plain

Abstract. The North China Plain (NCP) has become one of the most polluted regions in China, with the rapidly increasing economic growth in the past decades. High concentrations of ambient O3 and aerosol have been observed at urban as well as rural sites in the NCP. Most of the in situ observations of air pollutants have been conducted near the ground so that current knowledge about the vertical distributions of tropospheric O3 and aerosol over the NCP region is still limited. In this study, vertical profiles of O3 and size-resolved aerosol concentrations below 2.5 km were measured in summer 2014 over a rural site in the NCP, using an unmanned aerial vehicle (UAV) equipped with miniature analyzers. In addition, vertical profiles of aerosol scattering property in the lower troposphere and vertical profiles of O3 below 1 km were also observed at the site using a lidar and tethered balloon, respectively. The depths of the mixed layer and residual layer were determined according to the vertical gradients of lidar particle extinction and aerosol number concentration. Average O3 and size-resolved aerosol number concentration in both the mixed and residual layer were obtained from the data observed in seven UAV flights. The results show that during most of the flights the O3 levels above the top of mixed layer were higher than those below. Such a positive gradient in the vertical distribution of O3 makes the residual layer an important source of O3 in the mixed layer, particularly during the morning when the top of mixed layer is rapidly elevated. In contrast to O3, aerosol number concentration was normally higher in the mixed layer than in the residual layer, particularly in the early morning. Aerosol particles were overwhelmingly distributed in the size range &lt; 1 µm, showing slight differences between the mixed and residual layers. Our measurements confirm that the lower troposphere over the rural area of the NCP is largely impacted by anthropogenic pollutants locally emitted or transported from urban areas. Compared with the historic O3 vertical profiles over Beijing from the Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC), a strong increase in O3 can be found at all heights below 2.5 km in the decade from 2004 to 2014, with the largest enhancement of about 41.6 ppb. This indicates that the lower troposphere over the northern part of the NCP has experienced rapidly worsening photochemical pollution. This worsening trend in photochemical pollution deserves more attention in the future.

습도 변화에 따른 에어로졸의 농도 및 크기의 변화경향 파악

습도 변화에 따른 에어로졸의 농도 및 크기의 변화경향 파악

Predictions of size-resolved aerosol concentrations of ammonium, chloride and nitrate at a bayside site using EQUISOLV II

Measured ambient air concentrations of ammonium, chloride and nitrate were compared with concentrations produced by EQUISOLV II, an aerosol thermodynamic equilibrium model. The monitoring equipment was located ∼50 m from Old Tampa Bay at the eastern end of the Gandy Bridge in Tampa, FL. Size-segregated ion concentrations of ammonium, sodium, potassium, calcium, magnesium, fluoride, chloride, nitrite, nitrate, sulfate and phosphate were determined from 6- and 1-day integrated cascade impactor samples obtained in May and August 2001, respectively. EQUISOLV II was initialized with these ion concentrations by size bin, and by gas phase concentrations of the volatile species, acquired with a collocated annular denuder system. The model redistributed the ions between the size bins until gas and particle concentrations reached equilibrium. The model calculated predominantly fine particle ammonium and coarse particle chloride and nitrate. For the May sampling period, when the average relative humidity was below 65%, the model predicted the formation of seven solids KNO 3, K 2SO 4, (NH 4) 2SO 4, Na 2SO 4, NaCl, NaNO 3, and CaSO 4·2H 2O. The amounts of ammonium in the fine fraction and of nitrate and chloride in the coarse fraction were predicted within the combined measurement and modeling uncertainty in the majority of cases.

Development of a comprehensive, multiscale “one-atmosphere” modeling system: application to the Southern Appalachian Mountains

A comprehensive three-dimensional Eulerian photochemical model (URM-1ATM) was developed that simulates urban and regional gas and size-resolved aerosol concentrations of pollutants in the atmosphere and both wet and dry deposition. In this study, RAMS and EMS-95 are used to generate meteorological and emission input files, respectively. The modeling system is then applied to simulate the evolution, transport, and removal of atmospheric pollutants over the Eastern US for the 11–19 July 1995 episode. Performance statistics are calculated for ozone, speciated fine particles, and acid deposition mass fluxes.