Black carbon aerosols variation in Kathmandu valley, Nepal

Sharma, Ram Kumar; Bhattarai, Binod; Sapkota, Balkrishna; Gewali, Mohan B.; Kjeldstad, Berit

doi:10.1016/j.atmosenv.2012.09.023

Cited by 59 publications

(40 citation statements)

References 22 publications

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“…The AOD was approximately 0.30 in the summer monsoon, post-monsoon, and winter seasons. As many studies reported, these temporal variations are closely related to distinct seasonal monsoon circulations over South Asia including the Himalayan foothills (Sapkota et al, 2002; Sharma et al, 2012). Heavy precipitation in summer months (June-September) due to warm and marine air masses advected from the Indian Ocean by southerly flows (Carrico et al, 2003) efficiently removes atmospheric aerosols through the wet scavenging process (Sharma et al, 2012).…”

Section: Methodsmentioning

confidence: 99%

“…Here, we note that the climate seasons in Nepal are divided into winter (December-February), pre-monsoon (March-May), summer monsoon (June-September), and post-monsoon (October-November) seasons (Sharma et al, 2012). The AOD (675 nm) maxima were observed in the pre-monsoon season (0.63 ± 0.12).…”

Section: Methodsmentioning

confidence: 99%

“…As many studies reported, these temporal variations are closely related to distinct seasonal monsoon circulations over South Asia including the Himalayan foothills (Sapkota et al, 2002; Sharma et al, 2012). Heavy precipitation in summer months (June-September) due to warm and marine air masses advected from the Indian Ocean by southerly flows (Carrico et al, 2003) efficiently removes atmospheric aerosols through the wet scavenging process (Sharma et al, 2012). After the end of the summer monsoon, on the other hand, atmospheric aerosol loadings gradually increase under the dry and stable atmospheric conditions in the Himalayan foothills and local emissions also increase (e.g., increase in the biomass burning in houses in cold months and use of low-grade coal and biomass in brick factories and kilns, which are operational from mid-December to mid-April).…”

Section: Methodsmentioning

confidence: 99%

“…In addition, the Kathmandu Valley is located downwind of the Indo-Gangetic Plain region that experienced rapid growth in emissions and severe air quality degradation. All of this has resulted in elevated air pollution concentrations, especially during the dry season (Sapkota and Dhaubhadel, 2002;Shrestha and Shrestha, 2005;Sharma et al, 2012;Kiros et al, 2016). In addition, the bowl-shaped structure of the Kathmandu Valley, with a bottom altitude of ∼ 1.3 km and a rim of 2 to 2.8 km, and topography-induced circulations have made the air pollution more serious by limiting the transport of air pollutants out of the valley (Regmi et al, 2003;Panday and Prinn, 2009).…”

Section: Introductionmentioning

confidence: 99%

“…Panday and Prinn (2009) described a very regular pattern of morning and evening peaks of the CO and PM 10 concentrations occurring daily in the valley bottom, interspersed with low values in the afternoons and at night. Sharma et al (2012) communicated that the black carbon (BC) concentration shows a significant temporal variation with a monthly mean concentration varying between 14.9 and 3.0 µg m −3 . Chen et al (2015) observed that the total suspended particles (TSPs) and polycyclic aromatic hydrocarbons in the TSP were relatively high in the Kathmandu Valley compared with those observed in other parts of Asia.…”

Section: Introductionmentioning

confidence: 99%

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Wintertime aerosol optical and radiative properties in the Kathmandu Valley during the SusKat-ABC field campaign

et al. 2017

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Abstract. Particulate air pollution in the Kathmandu Valley has reached severe levels that are mainly due to uncontrolled emissions and the location of the urban area in a bowl-shaped basin with associated local wind circulations. The AERONET measurements from December 2012 to August 2014 revealed a mean aerosol optical depth (AOD) of approximately 0.30 at 675 nm during winter, which is similar to that of the post-monsoon but half of that of the pre-monsoon AOD (0.63). The distinct seasonal variations are closely related to regional-scale monsoon circulations over South Asia and emissions in the Kathmandu Valley. During the SusKat-ABC campaign (December 2012-February 2013, a noticeable increase in both aerosol scattering (σ s ; 313 → 577 Mm −1 at 550 nm) and absorption (σ a ; 98 → 145 Mm −1 at 520 nm) coefficients occurred before and after 4 January 2013. This can be attributed to the increase in wood-burned fires due to a temperature drop and the start of firing at nearby brick kilns. The σ s value in the Kathmandu Valley was a factor of 0.5 lower than that in polluted cities in India. The σ a value in the Kathmandu Valley was approximately 2 times higher than that at severely polluted urban sites in India. The aerosol mass scattering efficiency of 2.6 m 2 g −1 from PM 10 measurements in the Kathmandu Valley is similar to that reported in urban areas. However, the aerosol mass absorption efficiency was determined to be 11 m 2 g −1 from PM 10 measurements, which is higher than that reported in the literature for pure soot particles (7.5 ± 1.2 m 2 g −1 ). This might be due to the fact that most of the carbonaceous aerosols in the Kathmandu Valley were thought to be mostly externally mixed with other aerosols under dry conditions due to a short travel time from their sources. The σ s and σ a values and the equivalent black carbon (EBC) mass concentration reached up to 757 Mm −1 , 224 Mm −1 , and 29 µg m −3 at 08:00 LST (local standard time), respectively but decreased dramatically during the daytime (09:00-18:00 LST), to one-quarter of the morning average (06:00-09:00 LST) due to the development of valley winds and an atmospheric bounder layer. The σ s and σ a values and the EBC concentration remained almost constant during the night at the levels of 410 Mm −1 , 130 Mm −1 , and 17 µg m −3 , respectively. The average aerosol direct radiative forcings over the intensive measurement period were estimated to be −6.9 ± 1.4 W m −2 (top of the atmosphere) and −20.8 ± 4.6 W m −2 (surface). Therefore, the high atPublished by Copernicus Publications on behalf of the European Geosciences Union. 12618 C. Cho et al.: Wintertime aerosol optical and radiative properties in the Kathmandu Valley mospheric forcing (i.e., 13.9 ± 3.6 W m −2 ) and forcing efficiency (74.8 ± 24.2 W m −2 τ −1 ) can be attributed to the high portion of light-absorbing aerosols in the Kathmandu Valley, as indicated by the high black carbon (or elemental carbon) to sulphate ratio (1.5 ± 1.1).

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