Aerosol removal due to precipitation and wind forcings in Milan urban area

Cugerone, Katia; Michele, Carlo De; Ghezzi, Antonio; Gianelle, V.

doi:10.1016/j.jhydrol.2017.06.033

Cited by 28 publications

(16 citation statements)

References 20 publications

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“…Scavenging coefficients for the coarse mode (>1 µm) indicate a mean value of 5.8 × 10 −5 s −1 (with a standard deviation of 9.6 × 10 −5 s −1 ) and a median of 4.0 × 10 −5 s −1 (interquartile range: 3.5 × 10 −6 to 7.6 × 10 −5 s −1 ). The values obtained are comparable to those obtained by Cugerone et al, () in Italy (between 2 × 10 −5 and 5 × 10 −5 ) and lower than scavenging coefficients during thunderstorm rain events (Chate, ). This result indicates that the collection of aerosol particles by raindrops was more efficient in a highly electrified thunderstorm, mainly in the fine mode (Zhao et al, ).…”

Section: Resultssupporting

confidence: 89%

Below‐cloud scavenging of fine and coarse aerosol particles by rain: The role of raindrop size

Blanco-Alegre

Castro

Calvo

et al. 2018

Quart J Royal Meteoro Soc

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Below‐cloud aerosol scavenging is an important process to remove particles from the atmosphere. In this study, both precipitation (measured with a laser disdrometer registering drops between 0.125 and 8 mm) and atmospheric aerosol particles (measured with a Passive Cavity Aerosol Spectrometer Probe registering aerosol sizes between 0.1 and 24 µm) have been sampled on a 1 min basis. Based on 6 months of outdoor measurements in León (northwest Iberian Peninsula), the scavenging coefficients were calculated for the aerosol particles measured, with a mean value of 2.6 × 10−5 ± 6.0 × 10−5 s−1 for the fine mode and 5.8 × 10−5 ± 9.6 × 10−5 s−1 for the coarse mode in 54 rain events. Likewise, the particle concentration decreased during rain by 10%, and by 18% between the time before and after the rain. In the Greenfield Gap (sizes between 0.3 and 1 µm) the scavenging is less effective, mainly between 0.6 and 1 µm, than with smaller particles. The number of drops between 0.75 and 3 mm shows statistically significant (p < 0.05) negative correlations with the number of particles between 0.16 and 1.76 µm, thus illustrating the potential of those raindrops to favour the scavenging of particles of that size. In addition, there were statistically significant negative correlations between the total volume removed by falling drops (mm3/m3) and the variation of the number of particles in channels with diameters between 0.12 and 0.19 µm.

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Section: Resultssupporting

confidence: 89%

Below‐cloud scavenging of fine and coarse aerosol particles by rain: The role of raindrop size

Blanco-Alegre

Castro

Calvo

et al. 2018

Quart J Royal Meteoro Soc

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“…The occurrence of weather events, such as precipitation or high wind speed, indirectly causes a modification of the particle concentration, which often results in a decrease in number and mass of aerosol particles suspended in the lower atmosphere (Cugerone et al, 2018). In particular, the aerosol wet removal during rain events, known as the scavenging process, is caused by the vertical movement of the falling raindrops, which intercept the suspended aerosol particles and bring them to the ground (Seinfeld and Pandis, 2006).…”

Section: Weather Variables Influencementioning

confidence: 99%

On the functional form of particle number size distributions: influence of particle source and meteorological variables

et al. 2018

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Abstract. Particle number size distributions (PNSDs) have been collected periodically in the urban area of Milan, Italy, during 2011 and 2012 in winter and summer months. Moreover, comparable PNSD measurements were carried out in the rural mountain site of Oga-San Colombano (2250 m a.s.l.), Italy, during February 2005 and August 2011. The aerosol data have been measured through the use of optical particle counters in the size range 0.3-25 µm, with a time resolution of 1 min. The comparison of the PNSDs collected in the two sites has been done in terms of total number concentration, showing higher numbers in Milan (often exceeding 10 3 cm −3 in winter season) compared to Oga-San Colombano (not greater than 2×10 2 cm −3 ), as expected. The skewness-kurtosis plane has been used in order to provide a synoptic view, and select the best distribution family describing the empirical PNSD pattern. The four-parameter Johnson system-bounded distribution (called Johnson SB or JSB) has been tested for this aim, due to its great flexibility and ability to assume different shapes. The PNSD pattern has been found to be generally invariant under site and season changes. Nevertheless, several PNSDs belonging to the Milan winter season (generally more than 30 %) clearly deviate from the standard empirical pattern. The seasonal increase in the concentration of primary aerosols due to combustion processes in winter and the influence of weather variables throughout the year, such as precipitation and wind speed, could be considered plausible explanations of PNSD dynamics.

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“…Data availability. A subset of the dataset analysed during the current study is available in the http://ecohys.blogspot.it/p/data.html (Cugerone et al, 2016) repository. The complete dataset is available from the corresponding author on request.…”

Section: Discussionmentioning

confidence: 99%

“…The aerosol concentration variation due to the increase in particle emissions in the atmosphere is not the only cause of PNSD shape changes. The occurrence of weather events, such as precipitation or high wind speed, indirectly causes a modification of the particle concentration, which often results in a decrease in number and mass of aerosol particles suspended in the lower atmosphere (Cugerone et al, 2018). In particular, the aerosol wet removal during rain events, known as the scavenging process, is caused by the vertical movement of the falling raindrops, which intercept the suspended aerosol particles and bring them to the ground (Seinfeld and Pandis, 2006).…”

Section: Weather Variables Influencementioning

confidence: 99%

“…The great flexibility and versatility of this distribution, together with its boundedness (which matches the physical limitations of the analysed aerosol particles) make the Johnson SB a good candidate for this purpose. The use of this distribution has also been inspired by (Cugerone and De Michele, 2015;D'Adderio et al, 2016); and (Cugerone and De Michele, 2017), where the authors have recently demonstrated the accuracy of this probability function in modelling the number size distribution of drops at the ground, a particular case of PNSD. Furthermore, the outcomes of this study are in accordance with the works of (Yu and Standish, 1990) and (Liu and Liu, 1994), in which JSB was firstly proposed for this aim.…”

Section: Introductionmentioning

confidence: 99%

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Cugerone¹

2017

Preprint

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Particle number size distributions (PNSDs) have been collected periodically in the urban area of Milan, Italy, during 2011 and 2012 in winter and summer months. Moreover, comparable PNSD measurements were carried out in the rural mountain site of Oga-San Colombano (2250 m a.s.l.), Italy, during February 2005 and August 2011. The aerosol data have been measured through the use of optical particle counters in the size range 0.3-25 µm, with a time resolution of 1 min. The comparison of the PNSDs collected in the two sites has been done in terms of total number concentration, showing higher numbers in Milan (often exceeding 10 3 cm −3 in winter season) compared to Oga-San Colombano (not greater than 2×10 2 cm −3), as expected. The skewness-kurtosis plane has been used in order to provide a synoptic view, and select the best distribution family describing the empirical PNSD pattern. The four-parameter Johnson system-bounded distribution (called Johnson SB or JSB) has been tested for this aim, due to its great flexibility and ability to assume different shapes. The PNSD pattern has been found to be generally invariant under site and season changes. Nevertheless, several PNSDs belonging to the Milan winter season (generally more than 30 %) clearly deviate from the standard empirical pattern. The seasonal increase in the concentration of primary aerosols due to combustion processes in winter and the influence of weather variables throughout the year, such as precipitation and wind speed, could be considered plausible explanations of PNSD dynamics.

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Aerosol removal due to precipitation and wind forcings in Milan urban area

Cited by 28 publications

References 20 publications

Below‐cloud scavenging of fine and coarse aerosol particles by rain: The role of raindrop size

Below‐cloud scavenging of fine and coarse aerosol particles by rain: The role of raindrop size

On the functional form of particle number size distributions: influence of particle source and meteorological variables

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