Dynamics of PM2.5 concentrations in Kathmandu Valley, Nepal

Aryal, Rupak; Lee, Byeong–Kyu; Karki, Rahul; Gurung, Anup; Baral, Bivek; Byeon, Seung-Hyeok

doi:10.1016/j.jhazmat.2009.02.086

Cited by 44 publications

(37 citation statements)

References 21 publications

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“…The diurnal cycle of multimodal distributions (number of modes ≥3) indicates two distinct aerosol peaks, one in the morning (05:00 to 10:00 LT) and the other in evening hours (17:00 to 20:00 LT) for Site B. These time periods coincide with the transition period of boundary layer growth and collapse (inferred from the vertical profile of virtual potential temperature estimated from the radiosonde sounding obtained over Besisahar (Site B) (Barros and Lang, 2003). Likewise, the composite diurnal cycle of the total number concentration over the sampling periods for Site A and Site B clearly displays these distinct peaks (Fig.…”

Section: Diurnal Cyclementioning

confidence: 74%

“…Figure 2b shows the typical diurnal wind profile at Site B. UpValley wind strengthens from 09:00 to 14:00 LT and then begins to weaken afterwards in afternoon as mountain downslope winds begin to establish (north-westerly flow). The vertical profiles of wind from radiosonde data at lower levels (850-900 mb) in Besisahar during June 1999 reported by Barros and Lang (2003) also show the presence of northwesterly mountain wind from mid-night to morning, which transitions to up-valley wind around 09:00 LT in the morning and strengthens during daytime. These observations are consistent with the descriptive models provided by Defant (1949Defant ( , 1951, Vergeiner and Dreiseitl (1987), Rampanelli et al (2004), Mcnider et al (1984) for mountain valley circulations in narrow valleys.…”

Section: Regional Influence On Aerosol Spectramentioning

confidence: 81%

“…4d). The ERA Interim data at its coarse resolution cannot resolve the detailed wind fields in the inner regions of complex terrain proper but observed surface wind profiles suggest the transport of pollutants along the river valleys of Nepal from the southern lower plains via mountain-valley wind mechanisms (Zängl et al, 2000;Barros and Lang, 2003). On the other hand, the precipitation event in the morning of 5 June (Fig.…”

Section: Regional Influence On Aerosol Spectramentioning

confidence: 99%

“…These periods also coincide with the presence of synoptic scale haze as discussed above. Aryal et al (2009) discuss these accumulation effects for PM 2.5 measured in the Kathmandu Valley during the winter months caused by stagnant wind and temperature inversions. The observations from Site A in this study indicate that such accumulation effects are also present for Site A during the premonsoon season.…”

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confidence: 94%

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Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

2010

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Abstract. Aerosol particle number size distribution and chemical composition were measured at two low altitude sites, one urban and one relatively pristine valley, in Central Nepal during the 2009 pre-monsoon season (May-June). This is the first time that aerosol size distribution and chemical composition were measured simultaneously at lower elevations in the middle Himalayan region in Nepal. The aerosol size distribution was measured using a Scanning Mobility Particle Sizer (SMPS, 14-340 nm), and the chemical composition of the filter samples collected during the field campaign was analyzed in the laboratory. Teflon membrane filters were used for ion chromatography (IC) and watersoluble organic carbon and nitrogen analysis. Quartz fiber filters were used for organic carbon and elemental carbon analysis. Multi-lognormal fits to the measured aerosol size distribution indicated a consistent larger mode around 100 nm which is usually the oldest, most processed background aerosol. The smaller mode was located around 20 nm, which is indicative of fresh but not necessarily local aerosol. The diurnal cycle of the aerosol number concentration showed the presence of two peaks (early morning and evening), during the transitional periods of boundary layer growth and collapse. The increase in number concentration during the peak periods was observed for the entire size distribution. Although the possible contribution of local emissions in size ranges similar to the larger mode cannot be completely ruled out, another plausible explanation is the mixing of aged elevated aerosol in the residual layer during the morning period as suggested by previous studies. Similarly, the evening time concentration peaks when the boundary layer becomes shalCorrespondence to: A. P. Barros (barros@duke.edu) low concurrent with increase in local activity. A decrease in aerosol number concentration was observed during the nighttime with the development of cold (downslope) mountain winds that force the low level warmer air in the valley to rise. The mountain valley wind mechanisms induced by the topography along with the valley geometry appear to have a strong control in the diurnal cycle of the aerosol size distribution. During the sampling period, the chemical composition of PM 2.5 was dominated by organic matter at both sites. Organic carbon (OC) comprised the major fraction (64-68%) of the aerosol concentration followed by ionic species (24-26%, mainly SO 2− 4 and NH + 4 ). Elemental Carbon (EC) compromised 7-10% of the total composition and 27% of OC was found to be water soluble at both sites. The day-to-day variability observed in the time series of aerosol composition could be explained by the synoptic scale haze that extended to the sampling region from the Indian Gangetic Plain (IGP), and rainfall occurrence. In the presence of regional scale haze during dry periods, the mean volume aerosol concentration was found to increase and so did the aerosol mass concentrations.

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Section: Diurnal Cyclementioning

confidence: 74%

Section: Regional Influence On Aerosol Spectramentioning

confidence: 81%

Section: Regional Influence On Aerosol Spectramentioning

confidence: 99%

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confidence: 94%

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Chemical composition and aerosol size distribution of the middle mountain range in the Nepal Himalayas during the 2009 pre-monsoon season

2010

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“…Weather change is supposed to have direct and indirect effects on urban PM which in fact depends on sampling season, air mass origin and temperature. Fransen et al (2012) observed the higher levels of PM during the winter months due to more frequent temperature inversions in winter months combined with lack of precipitation (Aryal et al, 2008(Aryal et al, , 2009 The characterizations of PM are very important to perceive the morphological features of particle and their elemental composition and it can also provide the fundamental evidence for policy decision. The data is also very useful to analyze physicochemical characteristics, variability of particles in different seasons and their origin.…”

Section: Introductionmentioning

confidence: 99%

Study of Surface Morphology, Elemental Composition and Origin of Atmospheric Aerosols (PM2.5 and PM10) over Agra, India

Pipal

Jan

Satsangi

et al. 2014

Aerosol Air Qual. Res.

109

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In situ measurements of PM (PM 2.5 and PM 10 ) particles were carried out using a medium volume air sampler (offline) and particle number concentrations of PM were measured by a Grimm aerosol spectrophotometer (online) during the study period of 2010-2011. The morphology and elemental composition analyses of PM were performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectrometry (EDS), respectively. The average mass concentrations of PM 2.5 and PM 10 were 97.2 and 242.6 µg/m 3 at roadside (RD) and 121.2 and 230.5 µg/m 3 at a semirural (SR) site, respectively. These concentrations were substantially higher than the NAAQS, WHO and USEPA standards. The highest mass and number concentrations of PM 2.5 and PM 10 were observed during winter, followed by those during the post-monsoon period and summer, with the lowest in the monsoon period. SEM and EDS analysis of PM indicated the presence of soot, mineral, tarballs, fly ash, aluminosilicates/silica, fluorine, carbon rich, and Cl-Na rich particles. Of these particles, soot, tarballs, and F-C rich particles dominate in PM 2.5 , whereas mineral, aluminosilicates, and Cl-Na rich particles dominate in PM 10 . The morphology and elemental composition of the particles varied over the seasons due to atmospheric processing. The highest carbon concentration (56%) was observed in PM 2.5 during summer at the RD, while in the monsoon, postmonsoon period and winter the carbon concentration was ~9% lower at the RD as compared to the SR. However, the concentration of carbon in PM 10 was ~38% higher at the RD as compared to SR during both summer and winter. Air mass backward trajectory cluster analysis was performed, and the results indicate that the aerosol loadings over Agra are mainly transported from the Middle East and Arabian Sea during the summer and monsoon period, while during the pre-monsoon period and winter the aerosol loadings came from the northern region, and were due to the burning of biomass and coal, as well as other local activities.

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