Fine and ultrafine particles at a near–free tropospheric environment over the high-altitude station Hanle in the Trans-Himalaya: New particle formation and size distribution

Abstract

[1] Number-size distributions of ultrafine, fine, and accumulation mode aerosols in the size range 5-1300 nm have been measured regularly from the pristine, high-altitude (for 4520 m above mean sea level) station Hanle in the Trans-Himalaya during the summer and autumn (August-November) 2009. The total number concentration ranged from 80 to 8000 cm −3 with a mean value of 1150 cm −3. Examination of the temporal variations of the size distributions indicated that formation of new ultrafine particles from the precursor gases (probably transported from the valley regions) was highly probable during the forenoon hours of the day, especially during the summer when the insolation was abundant, the process becoming increasingly less efficient as the season progressed toward winter. The time of occurrence of maximum concentration was generally during the forenoon, a few hours after sunrise, and this time shifted to later parts of the day as the season progressed toward winter, probably associated with later sunrise and low solar elevations. The number-size distributions revealed two prominent modes: a nucleation mode with mode diameter at ∼16 nm and a consistent accumulation mode with the mode diameter ranging between 115 and 150 nm. Examining the temporal features with the air mass types, it was noticed that the number concentration increased, and the accumulation mode broadened when west Asian air mass prevailed. In summer (during August) the number concentrations tended to higher values associated with air mass from the Indian origin. The ratio of the Aitken to accumulation mode concentration indicated that the aerosol particles existing over the site are aged.Citation: Moorthy, K. K., et al. (2011), Fine and ultrafine particles at a near-free tropospheric environment over the highaltitude station Hanle in the Trans-Himalaya: New particle formation and size distribution,

Spring-Time Enhancement in Aerosol Burden over a High-Altitude Location in Western Trans-Himalaya:Results from Long-Term Observations

“…This observatory is also a part of the network of observatories under Aerosol Radiative Forcing over India (ARFI) project of ISRO-GBP, which is now known as ARFINET 23,24 . Some of the findings from this observatory have been published earlier [25][26][27][28][29][30][31] . These include the role of photochemistry in the new particle formation events at the freetropospheric altitudes 25 , temporal evolution and annual cycle in BC concentration over the Himalaya 26 , dust transport and associated changes in physical and optical properties of aerosols [27][28][29][30][31] and spring-time enhancement in aerosol optical depth (AOD) and BC over Hanle 30 .…”

“…Some of the findings from this observatory have been published earlier [25][26][27][28][29][30][31] . These include the role of photochemistry in the new particle formation events at the freetropospheric altitudes 25 , temporal evolution and annual cycle in BC concentration over the Himalaya 26 , dust transport and associated changes in physical and optical properties of aerosols [27][28][29][30][31] and spring-time enhancement in aerosol optical depth (AOD) and BC over Hanle 30 . While these earlier works are focused on characterization of aerosol optical and physical properties over Hanle, this article presents the quantitative estimation of spring-time enhancement in aerosol loading, its vertical structure and possible reasons for the inter-annual variability in springtime enhancement based on long-term observations of aerosol properties over Hanle during August 2009-December 2014.…”

“…Saraswati), among which some are snow-covered throughout the year while others experience seasonal precipitation, especially during winter (December-February) and summer (JulyAugust). More details of this near-free-tropospheric background location are available in the literature [25][26][27][28][29][30][31] . Figure 2 shows the prevailing surface meteorological conditions obtained using data from a collocated automatic weather station.…”

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

“…In sharp contrast, Hanle (32.78 • N, 78.96 • E; 4520 m a.m.s.l) is an extra-tropical high-altitude, nearpristine location in the western trans-Himalayas and southwest of the Tibetan plateau (Verma et al, 2009;Moorthy et al, 2011;Babu et al, 2011). Measurements were made from a mountaintop observatory, ∼ 300 m above the surrounding sparsely populated valley region.…”

“…While high-altitude locations at free tropospheric heights, which act as reservoirs for several gaseous species, witness NPF events on the synoptic scale through gas-particle conversion under favourable conditions, such as the availability of abundant UV radiation and moisture (Weber et al, 1995(Weber et al, , 1999Weingartner et al, 1999;Shaw, 2007;Nishita et al, 2007;Moorthy et al, 2011), urban and coastal environments have been observed to be potentially important sources of highly intense but localised aerosol formation bursts (O'Dowd et al, 1998a(O'Dowd et al, , b, 1999(O'Dowd et al, , 2002bVäkevä et al, 2000;Stanier et al, 2004;Ahlm et al, 2012) where abundant availability of moisture and volatile gases (anthropogenic, biogenic, and urban activities) exists. Distinctiveness in growth dynamics for these various environmental conditions is worth investigating.…”