The formation and growth of ultrafine particles in two contrasting environments: a case study

Abstract

Abstract. Formation of ultrafine particles and their subsequent growth have been examined during new particle formation (NPF) events in two contrasting environments under varying ambient conditions, one for a tropical semiurban coastal station, Trivandrum, and the other for a highaltitude free-tropospheric Himalayan location, Hanle. At Trivandrum, NPF bursts took place in the late evening/night hours, whereas at Hanle the burst was a daytime event. During the nucleation period, the total number concentration reached levels as high as ∼ 15 900 cm −3 at Trivandrum, whereas at Hanle, the total number concentration was ∼ 2700 cm −3 , indicating the abundant availability of precursors at Trivandrum and the pristine nature of Hanle. A sharp decrease was associated with NPF for the geometric mean diameter of the size distribution, and a large increase in the concentration of the particles in the nucleation regime (D p < 25 nm). Once formed, these (secondary) aerosols grew from nucleation (diameter D p < 25 nm) to Aitken (25 ≤ D p ≤ 100 nm) regime and beyond, to the accumulation size regimes (100 ≤ D p ≤ 1000 nm), with varying growth rates (GR) for the different size regimes at both the locations. A more rapid growth ∼ 50 nm h −1 was observed at Trivandrum, in contrast to Hanle where the growth rate ranged from 0.1 to 20 nm h −1 for the transformation from the nucleation to accumulation -a size regime that can potentially act as cloud condensation nuclei (CCN). The faster coagulation led to lifetimes of < 1 h for nucleation mode particles.

Seasonal Variation of Aerosol Size Distribution Data at the Puy de Dôme Station with Emphasis on the Boundary Layer/Free Troposphere Segregation

“…Other sources of particles in the FT can be nucleation of low-volatility gas-phase components into new particle clusters and their growth to larger sizes. As evidenced in earlier studies [16][17][18] new particle formation (NPF) may have specific characteristics at high altitudes. Once in the FT, aerosol particles have a longer residence time due to the lower frequency at which they are scavenged by clouds and precipitation, allowing them to be transported in the atmosphere for several days [19] increasing their impact on the climate.…”

Role of Aerosol Physicochemical Properties on Aerosol Hygroscopicity and Cloud Condensation Nuclei Activity in a Tropical Coastal Atmosphere

“…44−46 Among the two peaks, the first and more prominent peak (with N CN ∼ 20 720 cm −3 and N UFP ∼ 11 010 cm −3 ) occurs ∼07:00 to 08:00 h local time (LT) in the morning, about an hour after local sunrise. This peak is akin to the "fumigation peak" seen in primary pollutants such as aerosol black carbon 43 and is associated with the breaking of the nocturnal inversion by the thermals generated after sunrise, which brings pollutants to the surface from the residual mixed layer of the previous day. Subsequently, the number concentrations gradually decrease to reach the lowest values (N CN ∼ 4000 cm −3 and N UFP ∼ 1600 cm −3 ) during the afternoon/evening hours due to enhanced convective mixing and deepening of the ABL.…”

“…), is a tropical coastal station located at the south-western tip of peninsular India (Figure ). − Thumba is 10 km northwest of Thiruvananthapuram, a semi-urban location with a total population of ∼1.0 million (2011 census). The observational site, a flat coastal terrain, is located ∼500 m due east of the Arabian Sea coast within the sounding rocket launch station with no major urban and industrial activities.…”

“…Another prominent meteorological phenomenon at this coastal location is mesoscale land–sea-breeze circulation, which is more conspicuous during the dry months (December to May). The western coastal line is aligned roughly 145–325° azimuth, and the wind components arriving from 145 to 325° are considered the sea breeze (Figure a), and the offshore flow with wind components arriving from 325 to 145° constitutes the land breeze. − It may be noted that, because the city center is approximately 10 km away, the land breeze brings a considerable amount of anthropogenic aerosols during the night and the sea breeze brings comparatively cleaner marine air mass during the daytime.…”

“…The present study focuses on CCN closure over a tropical coastal station in the downwind of South Asian outflow to the south-eastern Arabian Sea, which experiences contrasting air masses within a day owing to mesoscale land–sea-breeze circulation and the atmospheric boundary layer (ABL) dynamics. , Earlier, Jayachandran et al reported CCN characteristics over this site during the southwest monsoon when the synoptic air mass is of marine origin. In the present study, CCN closure studies are carried out using nearly a month-long observations from a suite of aerosol instrumentation during the winter.…”