Air mass physiochemical characteristics over New Delhi: impacts on aerosol hygroscopicity and cloud condensation nuclei (CCN) formation

Arub, Zainab; Bhandari, Sahil; Gani, Shahzad; Apte, Joshua S.; Ruiz, Lea Hildebrandt; Habib, Gazala

doi:10.5194/acp-20-6953-2020

Cited by 35 publications

(31 citation statements)

References 80 publications

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“…This suggests the importance of aerosol particle number and size for effective CCN activation, consistent with previous studies (Dusek et al, 2006;Gunthe et al, 2009Gunthe et al, , 2011. The high CCN efficiency achieved at the highest measured S = 0.69% during both strong and weak inversion periods (70% and 74%,respectively) also verifies the high activated fractions estimated by Arub et al (2020).…”

Section: Tablesupporting

confidence: 90%

“…Studies on the influence of meteorology on aerosol properties show that under uniform and unchanged sources of emissions, the extreme lowering of the PBL below 100 m during winters builds up extreme particulate matter concentrations, driving the Air Quality Index to hazardous levels (Bhandari et al, 2020;Dumka et al, 2019;Gani et al, 2019;Mandal et al, 2014;Murthy et al, 2020;Ojha et al, 2020). The influence of air mass history has also been reported in Delhi using back trajectory analysis (Arub et al, 2020;Jaiprakash et al, 2017). A comprehensive analysis provided in this study combining remote sensing and modeling approaches with measurements of CCN activity at 11 different supersaturations is unprecedented.…”

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confidence: 93%

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Planetary Boundary Layer Height Modulates Aerosol—Water Vapor Interactions During Winter in the Megacity of Delhi

et al. 2021

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The megacity of Delhi is located within the Indo-Gangetic Plain (IGP) and is one of the major sources of anthropogenic air pollution. It is a continental metropolitan area in a large valley south of the Himalayas, which causes the air masses to be constrained within the IGP (Figure 1). The air masses are vulnerable to high levels of particulate matter emissions from the megacity all year round (Bhandari et al., 2020), since it is a fast-growing urban agglomeration (Jain et al., 2016;Paul et al., 2021). During winter, a strong radiative thermal inversion causes the megacity to be enveloped by a shallow planetary boundary layer (PBL) in the nighttime, resulting in high relative humidity (RH) and aerosol mass burden (Arun et al., 2018;Murthy et al., 2020). The cold, humid and polluted conditions coupled with low wind speeds make the landlocked atmosphere conducive to fog and haze formation (Dhangar et al., 2021;Dumka et al., 2019;Ojha et al., 2020). Moreover, the aerosols in Delhi have enhanced water uptake ability as reported in the companion study by Gunthe et al. (2021), which can facilitate multiphase processes for formation of aerosols and thereby cause drastic visibility deterioration.

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confidence: 90%

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confidence: 93%

Planetary Boundary Layer Height Modulates Aerosol—Water Vapor Interactions During Winter in the Megacity of Delhi

et al. 2021

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“…The average  values were considerably smaller than for regional or remote locations (Paramonov et al, 2015;Schmale et al, 2018). There are few hygroscopicity parameters reported specifically for urban environments, and even less for city centres (Gunthe et al, 2011;Rose et al, 2010Rose et al, , 2011Meng et al, 2014;Arub et al, 2020). The present data can also be linked to the average or effective hygroscopicity parameters found in field measurements and chamber studies for fresh soot particles of <0.01, for secondary organic aerosol of approximately 0.10 and for inorganic aerosol fraction of ca.…”

Section: Hygroscopicity Parameterssupporting

confidence: 61%

Cloud droplet activation in a continental Central European urban environment

Salma¹,

Thén²,

Vörösmarty³

et al. 2021

Preprint

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Abstract. Collocated measurements by condensation particle counter, differential mobility particle sizer and cloud condensational nuclei counter instruments were realised in parallel in central Budapest from 15 April 2019 to 14 April 2020 to gain insight into the droplet activation behaviour of urban aerosol particles. The median total particle number concentration was 10.1 × 103 cm−3. The median concentrations of cloud condensation nuclei (CCN) at water vapour supersaturations (Ss) of 0.1, 0.2, 0.3, 0.5 and 1.0 % were 0.59, 1.09, 1.39, 1.80 and 2.5 × 103 cm−3, respectively. They represented from 7 to 27 % of the total particles. The effective critical dry particle diameters (dc,eff) were derived utilising the CCN concentrations and particle number size distributions. Their medians were 207, 149, 126, 105 and 80 nm, respectively. They were all positioned within the accumulation mode of the typical particle number size distribution. Their frequency distributions revealed a single peak, which geometric standard deviation increased monotonically with S. The broadening indicated larger time variability in the activation properties of smaller particles. The frequency distributions also showed a fine structure. Its several compositional elements seemed to change in a tendentious manner with S. They were related to the size-dependent chemical composition and external mixtures of particles. The relationships between the critical S and dc,eff suggested that the urban aerosol particles in Budapest with a diameter larger than approximately 130 nm showed similar hygroscopicity than the continental aerosol in general, while the smaller particles appeared to be less hygroscopic than that. Seasonal cycling of the CCN concentrations and activation fractions implied modest alterations and for the larger Ss only. They likely reflected the changes in particle number concentrations, chemical composition and mixing state of particles. The seasonal dependencies for dc,eff were featureless, which indicated that the urban particles exhibited more or less similar droplet activation properties over the measurement year. This is different from non-urban locations. The hygroscopicity parameters (κ values) were computed without determining time-dependent chemical composition of particles. Their medians were 0.16, 0.10, 0.07, 0.04 and 0.02, respectively. The averages suggested that the larger particles exhibited considerably higher hygroscopicity than the smaller particles. The urban aerosol was characterised by substantially smaller kappa values than for regional or remote locations. All these could be virtually linked to specific source composition in cities. The relatively large variability in the hygroscopicity parameter sets for a given S emphasized that their individual values represented the CCN population in the ambient air, while the averages stood mainly for the particles with a size close to the effective critical dry particle diameters.

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“…The average κ values were considerably smaller than those in regional or remote locations (Paramonov et al, 2015;Schmale et al, 2018). Only a few hygroscopicity parameters specifically for urban environments have been reported, and even fewer for city centres (Gunthe et al, 2011;Rose et al, 2010Meng et al, 2014;Arub et al, 2020). The present data can also be linked to the average or effective hygroscopicity parameters found in field measurements and chamber studies for fresh soot particles (< 0.01), for a secondary organic aerosol (approximately 0.10) and for an inor- (Rose et al, 2011).…”

Section: Hygroscopicity Parameterssupporting

confidence: 42%

Cloud activation properties of aerosol particles in a continental Central European urban environment

Salma

Thén²,

Vörösmarty³

et al. 2021

Atmos. Chem. Phys.

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Abstract. Collocated measurements using a condensation particle counter, differential mobility particle sizer and cloud condensation nuclei counter were realised in parallel in central Budapest from 15 April 2019 to 14 April 2020 to gain insight into the cloud activation properties of urban aerosol particles. The median total particle number concentration was 10.1 × 103 cm−3. The median concentrations of cloud condensation nuclei (CCN) at water vapour supersaturation (S) values of 0.1 %, 0.2 %, 0.3 %, 0.5 % and 1.0 % were 0.59, 1.09, 1.39, 1.80 and 2.5 × 103 cm−3, respectively. The CCN concentrations represented 7–27 % of all particles. The CCN concentrations were considerably larger but the activation fractions were systematically substantially smaller than observed in regional or remote locations. The effective critical dry particle diameters (dc,eff) were derived utilising the CCN concentrations and particle number size distributions. Their median values at the five supersaturation values considered were 207, 149, 126, 105 and 80 nm, respectively; all of these diameters were positioned within the accumulation mode of the typical particle number size distribution. Their frequency distributions revealed a single peak for which the geometric standard deviation increased monotonically with S. This broadening indicated high time variability in the activating properties of smaller particles. The frequency distributions also showed fine structure, with several compositional elements that seemed to reveal a consistent or monotonical tendency with S. The relationships between the critical S and dc,eff suggest that urban aerosol particles in Budapest with diameters larger than approximately 130 nm showed similar hydroscopicity to corresponding continental aerosol particles, whereas smaller particles in Budapest were less hygroscopic than corresponding continental aerosol particles. Only modest seasonal cycling in CCN concentrations and activation fractions was seen, and only for large S values. This cycling likely reflects changes in the number concentration, chemical composition and mixing state of the particles. The seasonal dependencies of dc,eff were featureless, indicating that the droplet activation properties of the urban particles remained more or less the same throughout the year. This is again different from what is seen in non-urban locations. Hygroscopicity parameters (κ values) were computed without determining the time-dependent chemical composition of the particles. The median values for κ were 0.15, 0.10, 0.07, 0.04 and 0.02, respectively, at the five supersaturation values considered. The averages suggested that the larger particles were considerably more hygroscopic than the smaller particles. We found that the κ values for the urban aerosol were substantially smaller than those previously reported for aerosols in regional or remote locations. All of these characteristics can be linked to the specific source composition of particles in cities. The relatively large variability in the hygroscopicity parameters for a given S emphasises that the individual values represent the CCN population in ambient air while the average hygroscopicity parameter mainly corresponds to particles with sizes close to the effective critical dry particle diameter.

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Air mass physiochemical characteristics over New Delhi: impacts on aerosol hygroscopicity and cloud condensation nuclei (CCN) formation

Cited by 35 publications

References 80 publications

Planetary Boundary Layer Height Modulates Aerosol—Water Vapor Interactions During Winter in the Megacity of Delhi

Planetary Boundary Layer Height Modulates Aerosol—Water Vapor Interactions During Winter in the Megacity of Delhi

Cloud droplet activation in a continental Central European urban environment

Cloud activation properties of aerosol particles in a continental Central European urban environment

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