Cloud condensation nuclei characteristics during the Indian summer monsoon over a rain-shadow region

Abstract. Continuous aerosol and cloud condensation nuclei (CCN) measurements carried out at the ground observational facility situated in the rain-shadow region of the Indian subcontinent are illustrated. These observations were part of the Cloud Aerosol Interaction Precipitation Enhancement Experiment (CAIPEEX) during the Indian summer monsoon season (June to September) of 2018. Observations are classified as dry–continental (monsoon break) and wet–marine (monsoon active) according to the air mass history. CCN concentrations measured for a range of supersaturations (0.2 %–1.2 %) are parameterized using Twomey's empirical relationship. CCN concentrations at low (0.2 %) supersaturation (SS) were high (>1000cm-3) during continental conditions and observed together with high black carbon (BC∼2000ngm-3) and columnar aerosol loading. During the marine air mass conditions, CCN concentrations diminished to ∼350cm-3 at 0.3 % SS and low aerosol loading persisted (BC∼800ngm-3). High CCN activation fraction (AF) of ≅0.55 (at 0.3 % SS) was observed before the monsoon rainfall, which reduced to ≅0.15 during the marine air mass and enhanced to ≅0.32 after that. There was mostly monomodal aerosol number size distribution (NSD) with a mean geometric mean diameter (GMD) of ≅85 nm, with least (≅9 %) contribution from nucleation mode (<30 nm) particles persisted before the monsoon, while multimode NSD with ≅19 % of nucleation mode particles was found during the marine air mass. Critical activation diameters (dcri) for 0.3 % SS were found to be about 72, 169, and 121 nm prior to, during, and after the marine conditions, respectively. The better association of CCN with aerosol absorption, and the concurrent accumulation mode particles during continental conditions, points to the possibility of aged (oxygenated) carbonaceous aerosols enhancing the CCN activity prior to the marine conditions. An enhancement in CCN concentrations and k values during the daytime along with absorption Ångström exponent was observed during the marine conditions. Best closure obtained using measured critical diameter and ammonium sulfate composition during continental conditions emphasizes the role of aged aerosols contributing to the accumulation mode, enhancing the CCN efficiency. The overestimation of CCN and less hygroscopicity of accumulation mode aerosols during the marine air mass indicate the role of size-dependent aerosol composition in CCN activity during the period.

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CCN characteristics during the Indian Summer Monsoon over a rain-shadow region

10.5194/acp-2020-45 ◽

2020 ◽

Author(s):

Venugopalan Nair Jayachandran ◽

Mercy Varghese ◽

Palani Murugavel ◽

Kiran S. Todekar ◽

Shivdas P. Bankar ◽

...

Keyword(s):

Summer Monsoon ◽

Indian Summer Monsoon ◽

Monsoon Season ◽

Cloud Condensation Nuclei ◽

Geometric Mean ◽

Empirical Relationship ◽

Shadow Region ◽

Air Mass ◽

Aerosol Loading ◽

Marine Air

Abstract. Continuous aerosol and Cloud Condensation Nuclei (CCN) measurements carried out at the ground observational facility situated in the rain-shadow region of the Indian sub-continent are illustrated. These observations were part of the Cloud-Aerosol Interaction Precipitation Enhancement EXperiment (CAIPEEX) during the Indian Summer Monsoon season (June to September) of 2018. Observations are classified as dry-continental (monsoon break) and wet-marine (monsoon active) according to air mass history. CCN concentrations measured for a range of supersaturations (0.2–1.2 %) are parameterized using Twomey's empirical relationship. CCN concentrations even at low (0.2 %) supersaturation (SS) were high (> 1,000 cm-3) during continental conditions associated with high black carbon (BC~2,000 ng m-3) and columnar aerosol loading. During the marine air mass conditions, CCN concentrations diminished to ~ 350 cm-3 at 0.3 % SS and low aerosol loading persisted (BC~900 ng m-3). High CCN activation fraction (AF) of ~ 0.55 (at 0.3 % SS) were observed before the monsoon rainfall, which reduced to ~ 0.15 during the monsoon and enhanced to ~ 0.32 after that. Mostly mono-modal aerosol number-size distribution (NSD) with a mean geometric mean diameter (GMD) of ~ 85 nm, with least (~ 9 %) contribution from nucleation mode (

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Altitude profiles of cloud condensation nuclei characteristics across the Indo-Gangetic Plain prior to the onset of the Indian summer monsoon

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-561-2020 ◽

2020 ◽

Vol 20 (1) ◽

pp. 561-576 ◽

Cited By ~ 7

Author(s):

Venugopalan Nair Jayachandran ◽

Surendran Nair Suresh Babu ◽

Aditya Vaishya ◽

Mukunda M. Gogoi ◽

Vijayakumar S. Nair ◽

...

Keyword(s):

Optical Properties ◽

Summer Monsoon ◽

Indian Summer Monsoon ◽

Cloud Condensation Nuclei ◽

Condensation Nuclei ◽

Aerosol Optical Properties ◽

Gangetic Plain ◽

Air Mass ◽

Activation Efficiency ◽

Indo Gangetic Plain

Abstract. Concurrent measurements of the altitude profiles of the concentration of cloud condensation nuclei (CCN), as a function of supersaturation (ranging from 0.2 % to 1.0 %), and aerosol optical properties (scattering and absorption coefficients) were carried out aboard an instrumented aircraft across the Indo-Gangetic Plain (IGP) just prior to the onset of the Indian summer monsoon (ISM) of 2016. The experiment was conducted under the aegis of the combined South-West Asian Aerosol–Monsoon Interactions and Regional Aerosol Warming Experiment (SWAAMI–RAWEX) campaign. The measurements covered coastal, urban and arid environments. In general, the CCN concentration was highest in the central IGP, decreasing spatially from east to west above the planetary boundary layer (PBL), which is ∼1.5 km for the IGP during pre-monsoon period. Despite this, the CCN activation efficiency at 0.4 % supersaturation was, interestingly, the highest over the eastern IGP (∼72 %), followed by that in the west (∼61 %), and it was the least over the central IGP (∼24 %) within the PBL. In general, higher activation efficiency is noticed above the PBL than below it. The central IGP showed remarkably low CCN activation efficiency at all altitudes, which appears to be associated with high black carbon (BC) mass concentration there, indicating the role of anthropogenic sources in suppressing the CCN efficiency. These first-ever CCN measurements over the western IGP, encompassing “the Great Indian Desert” also known as “the Thar Desert”, showed high CCN efficiency, ∼61 % at 0.4 % supersaturation, indicating the hygroscopic nature of the dust. The vertical structure of CCN properties is found to be air mass dependent, with higher activation efficiency even over the central IGP during the prevalence of marine air mass. Wet scavenging associated with precipitation episodes seems to have reduced the CCN activation efficiency below cloud level. An empirical relation has emerged between the CCN concentration and the scattering aerosol index (AI), which would facilitate the prediction of CCN from aerosol optical properties.

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Cloud condensation nuclei over the Bay of Bengal during the Indian summer monsoon

Advances in Atmospheric Sciences ◽

10.1007/s00376-017-6331-z ◽

2018 ◽

Vol 35 (2) ◽

pp. 218-223

Author(s):

D. M. Chate ◽

R. T. Waghmare ◽

C. K. Jena ◽

V. Gopalakrishnan ◽

P. Murugavel ◽

...

Keyword(s):

Summer Monsoon ◽

Indian Summer Monsoon ◽

Bay Of Bengal ◽

Cloud Condensation Nuclei ◽

Condensation Nuclei

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Submicron aerosols at thirteen diversified sites in China: size distribution, new particle formation and corresponding contribution to cloud condensation nuclei production

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-15149-2014 ◽

2014 ◽

Vol 14 (10) ◽

pp. 15149-15189 ◽

Cited By ~ 2

Author(s):

J. F. Peng ◽

M. Hu ◽

Z. B. Wang ◽

X. F. Huang ◽

P. Kumar ◽

...

Keyword(s):

Size Distribution ◽

Particle Number ◽

Cloud Condensation Nuclei ◽

Particle Formation ◽

New Particle Formation ◽

Condensation Nuclei ◽

Accumulation Mode ◽

Nucleation Mode ◽

Secondary Formation ◽

Urban Sites

Abstract. Understanding the particle number size distributions in diversified atmospheric environments is important in order to design mitigation strategies related to submicron particles and their effect on regional air quality, haze and human health. In this study, we conducted 15 different field measurement campaigns, each one-month long, between 2007 and 2011 at 13 individual sites in China. These were 5 urban sites, 4 regional sites, 3 coastal/background sites and one ship cruise measurement along eastern coastline of China. Size resolved particles were measured in the 15–600 nm size range. The median particle number concentrations (PNC) were found to vary in the range of 1.1–2.2 × 104 cm−3 at urban sites, 0.8–1.5 × 104 cm−3 at regional sites, 0.4–0.6 × 104 cm−3 at coastal/background sites, and 0.5 × 104 cm−3 during cruise measurements. Peak diameters at each of these sites varied greatly from 24 nm to 115 nm. Particles in the 15–25 nm (nucleation mode), 25–100 nm (Aitken mode) and 100–600 nm (accumulation mode) range showed different characteristics at each of the studied sites, indicating the features of primary emissions and secondary formation in these diversified atmospheric environments. Diurnal variations show a build-up of accumulation mode particles belt at regional sites, suggesting the contribution of regional secondary aerosol pollution. Frequencies of new particle formation (NPF) events were much higher at urban and regional sites than at coastal sites and cruise measurement. The average growth rates (GRs) of nucleation mode particles were 8.0–10.9 nm h−1 at urban sites, 7.4–13.6 nm h−1 at regional sites and 2.8–7.5 nm h−1 at both coastal and cruise measurement sites. The high gaseous precursors and strong oxidation at urban and regional sites not only favored the formation of particles, but also accelerated the growth rate of the nucleation mode particles. No significant difference in condensation sink (CS) during NPF days were observed among different site types, suggesting that the NPF events in background area were more influenced by the pollutant transport. In addition, average contributions of NPF events to potential cloud condensation nuclei (CCN) at 0.2% super-saturation in the afternoon of all sampling days were calculated as 11% and 6% at urban sites and regional sites, respectively. On the other hand, NPF events at coastal and cruise measurement sites had little impact on potential production of CCN. This study provides a large dataset of aerosol size distribution in diversified atmosphere of China, improving our general understanding of emission, secondary formation, new particles formation and corresponding CCN activity of submicron aerosols in Chinese environments.

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Submicron aerosols at thirteen diversified sites in China: size distribution, new particle formation and corresponding contribution to cloud condensation nuclei production

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-10249-2014 ◽

2014 ◽

Vol 14 (18) ◽

pp. 10249-10265 ◽

Cited By ~ 51

Author(s):

J. F. Peng ◽

M. Hu ◽

Z. B. Wang ◽

X. F. Huang ◽

P. Kumar ◽

...

Keyword(s):

Size Distribution ◽

Particle Number ◽

Cloud Condensation Nuclei ◽

Particle Formation ◽

New Particle Formation ◽

Condensation Nuclei ◽

Accumulation Mode ◽

Nucleation Mode ◽

Secondary Formation ◽

Urban Sites

Abstract. Understanding the particle number size distributions in diversified atmospheric environments is important in order to design mitigation strategies related to submicron particles and their effects on regional air quality, haze and human health. In this study, we conducted 15 different field measurement campaigns between 2007 and 2011 at 13 individual sites in China, including five urban sites, four regional sites, three coastal/background sites and one ship cruise measurement along eastern coastline of China. Size resolved particles were measured in the 15–600 nm size range. The median particle number concentrations (PNCs) were found to vary in the range of 1.1−2.2 × 104 cm−3 at urban sites, 0.8−1.5 × 104 cm−3 at regional sites, 0.4−0.6 × 104 cm−3 at coastal/background sites, and 0.5 × 104 cm−3 during cruise measurement. Peak diameters at each of these sites varied greatly from 24 to 115 nm. Particles in the 15–25 nm (nucleation mode), 25–100 nm (Aitken mode) and 100–600 nm (accumulation mode) range showed different characteristics at each sites, indicating the features of primary emissions and secondary formation in these diversified atmospheric environments. Diurnal variations show a build-up of accumulation mode particles belt at regional sites, suggesting the contribution of regional secondary aerosol pollution. Frequencies of new particle formation (NPF) events were much higher at urban and regional sites than at coastal sites and during cruise measurement. The average growth rates (GRs) of nucleation mode particles were 8.0–10.9 nm h−1 at urban sites, 7.4–13.6 nm h−1 at regional sites and 2.8–7.5 nm h−1 at coastal sites and during cruise measurement. The high gaseous precursors and strong oxidation at urban and regional sites not only favored the formation of particles, but also accelerated the growth rate of the nucleation mode particles. No significant difference in condensation sink (CS) during NPF days were observed among different site types, suggesting that the NPF events in background areas were more influenced by the pollutant transport. In addition, average contributions of NPF events to potential cloud condensation nuclei (CCN) at 0.2% super-saturation in the afternoon of all sampling days were calculated as 11% and 6% at urban sites and regional sites, respectively. On the other hand, NPF events at coastal sites and during cruise measurement had little impact on potential production of CCN. This study provides a large data set of particle size distribution in diversified atmosphere of China, improving our general understanding of emission, secondary formation, new particle formation and corresponding CCN activity of submicron aerosols in Chinese environments.

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