Atmospheric turbidity over Kathmandu valley

Sapkota, Balkrishna; Dhaubhadel, Rajan

doi:10.1016/s1352-2310(01)00582-9

Cited by 32 publications

(29 citation statements)

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“…Some researchers have attributed the dark haze over Kathmandu valley to the presence of soot particles (Sapkota and Dhaubhadel, 2002). Others investigated the aerosol chemical properties in Nagarkot, at the rim of the Kathmandu valley, and found that the aerosol featured a dominant contribution from carbon, likely from fuel combustion and biomass burning processes in the Kathmandu valley (Carrico et al, 2003).…”

Section: Aerosol Surface and Ground Reactive Surfacementioning

confidence: 99%

Observations of high rates of NO<sub>2</sub>-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Galle

Panday

et al. 2009

Atmos. Chem. Phys.

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Abstract. Nitrous acid (HONO) plays a significant role in the atmosphere, especially in the polluted troposphere. Its photolysis after sunrise is an important source of hydroxyl free radicals (OH). Measurements of nitrous acid and other pollutants were carried out in the Kathmandu urban atmosphere during January-February 2003, contributing to the sparse knowledge of nitrous acid in South Asia. The results showed average nocturnal levels of HONO (1.7±0.8 ppbv), NO 2 (17.9±10.2 ppbv), and PM 10 (0.18±0.11 mg m −3 ) in urban air in Kathmandu. Surprisingly high ratios of chemically formed secondary [HONO] to [NO 2 ] (up to 30%) were found, which indicates unexpectedly efficient chemical conversion of NO 2 to HONO in Kathmandu. The ratios of [HONO]/[NO 2 ] at night were found to be much higher than previously reported values from measurements in urban air in Europe, North America and Asia. The influences of aerosol surface, ground reactive surface, and relative humidity on NO 2 -HONO chemical conversion were discussed. The high humidity, strong and low inversion layer at night, and high aerosol pollution burden in Kathmandu may explain the particularly efficient conversion of NO 2 to HONO.

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Section: Aerosol Surface and Ground Reactive Surfacementioning

confidence: 99%

Observations of high rates of NO<sub>2</sub>-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Galle

Panday

et al. 2009

Atmos. Chem. Phys.

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“…The valley is located within the Middle Mountain Zone, between 27°37 0 30 00 N and 27°45 0 00 00 N, and 85°15 0 00 00 E and 85°22 0 30 00 E (Sapkota and Dhaubhadel, 2002), and has a basin-like shape with a diameter of 30 km E-W and 25 km N-S. The surrounding mountains are between 2000 and 2800 m above sea level (a.s.l.)…”

Section: Sampling Sites Sampling and Standard Analysismentioning

confidence: 99%

Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in urban soils from Kathmandu, Nepal

Aichner

Glaser

Zech

2007

Organic Geochemistry

123

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Kathmandu, the capital of Nepal, faces increasing environmental problems such as heavy air pollution and lack of proper waste management. The aim of this study was to examine if the soils are also affected by pollution, with the focus on polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The sum of 20 PAHs in surface soils ranged between 184 and 10279 lg kg À1 . The most abundant PAHs were perylene (14.6%), benzo(b+j+k)flouranthene (10.7%), naphthalene (10.7%) and phenanthrene (9.8%), with perylene concentrations varying strongly. The significantly more positive d 13 C values of perylene in samples with elevated concentrations indicate biological production, possibly by anaerobic degradation of perylene quinones. PAH ratios also indicate the influence of petrogenic PAH sources, especially at petrol stations and some street samples. The sum of 12 PCBs ranged from 356 to 44710 ng kg À1 . The most abundant were congeners 52 (19.4%), 101 (14.3%), 118 (13.4%) and 138 (11.7%). The low PCB concentrations and pattern were interpreted as a diffuse background contamination being the main PCB source in the urban soils. Indications for recent contamination were found in river sediments from the inner city, as well as in industrial and street samples. Classified by land use, the samples taken from the gutter contained the highest PAH and PCB concentrations as a result of accumulation. The lowest values were found in surface soils from Swayambunath (a park) and a garden area. A gradual decrease in concentration with depth was present for both compound classes in the profiles sampled at Swayambunath. No trend was visible in the garden profiles as a result of soil disturbance of the soil by agricultural treatment. Enhanced microbial degradation and volatilization in the warm/humid monsoon climate is probably the main cause for low pollutant concentrations. Increased photodegradation and the short accumulation period might be other important factors. Concerning its state of soil pollution, Kathmandu fits rather well into a global distribution pattern of persistent organic pollutants, with high concentrations in temperate (higher latitude) regions and very low ones in the tropics (lower latitude regions) due to global distillation.

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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: 84%

“…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%

“…Many studies reported various atmospheric compounds, mainly gases and aerosols, and associated temporal patterns with meteorological conditions in the Kathmandu Valley (Sapkota and Dhaubhadel, 2002;Shrestha and Shrestha, 2005;Stone et al, 2010;Chen et al, 2015;Kim et al, 2015;Kiros et al, 2016). 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.…”

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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Atmospheric turbidity over Kathmandu valley

Cited by 32 publications

References 10 publications

Observations of high rates of NO<sub>2</sub>-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Observations of high rates of NO<sub>2</sub>-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in urban soils from Kathmandu, Nepal

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

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Atmospheric turbidity over Kathmandu valley

Cited by 32 publications

References 10 publications

Observations of high rates of NO&lt;sub&gt;2&lt;/sub&gt;-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Observations of high rates of NO&lt;sub&gt;2&lt;/sub&gt;-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in urban soils from Kathmandu, Nepal

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

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Observations of high rates of NO<sub>2</sub>-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal

Observations of high rates of NO<sub>2</sub>-HONO conversion in the nocturnal atmospheric boundary layer in Kathmandu, Nepal