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  • 1
    Publication Date: 2020-03-12
    Language: English
    Type: info:eu-repo/semantics/article
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  • 2
    Publication Date: 2020-03-12
    Description: The properties and the vertical structure of the mixing layer as part of the planetary boundary layer are of key importance for local air quality. They have a substantial impact on the vertical dispersion of pollutants in the lower atmosphere and thus on their concentrations near the surface. In this study, ceilometer measurements taken within the framework of the SusKat project (Sustainable Atmosphere for the Kathmandu Valley) are used to investigate the mixing layer height in the Kathmandu Valley, Nepal. The applied method is based on the assumption that the aerosol concentration is nearly constant in the vertical and distinctly higher within the mixing layer than in the air above. Thus, the height with the steepest gradient within the ceilometer backscatter profile marks the top of the mixing layer. Ceilometer and black carbon (BC) measurements conducted from March 2013 through February 2014 provide a unique and important dataset for the analysis of the meteorological and air quality conditions in the Kathmandu Valley. In this study the mean diurnal cycle of the mixing layer height in the Kathmandu Valley for each season (pre-monsoon, monsoon, post-monsoon and winter season) and its dependency on the meteorological situation is investigated. In addition, the impact of the mixing layer height on the BC concentration is analyzed and compared to the relevance of other important processes such as emissions, horizontal advection and deposition. In all seasons the diurnal cycle is typically characterized by low mixing heights during the night, gradually increasing after sun rise reaching to maximum values in the afternoon before decreasing again. Seasonal differences can be seen particularly in the height of the mixing layer, e.g. from on average 153/1200 m (pre-monsoon) to 241/755 m (monsoon season) during the night/day, and the duration of enhanced mixing layer heights during daytime (around 12 hours (pre-monsoon season) to 8 hours (winter)). During the monsoon season, the observed diurnal cycle typically shows the lowest amplitude and the lowest mixing height during the day and the highest in the night and morning hours of all seasons. These characteristics can mainly be explained with frequently present clouds and the associated lack of incoming solar radiation and outgoing longwave radiation. In general there is a clear anti-correlation of the BC concentration and the mixing layer height although this relation is less pronounced in the monsoon season. The shape and magnitude of the BC diurnal cycle differs between the seasons (e.g., daily maximum concentration from around 6 to 50 μg/m3 depending on the season). This is partly due to the different meteorological conditions including the mixing layer height but also caused by the different (seasonal and diurnal) time profiles of the main emission sources. From late December to April, for instance, brick kilns are major emitters of black carbon. The brick kilns emit continuously throughout the day whereas in the other months sources with more pronounced diurnal cycles, such as traffic and cooking activities, are dominating the total emissions.
    Language: English
    Type: info:eu-repo/semantics/conferenceObject
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  • 3
    Publication Date: 2020-03-12
    Description: The Kathmandu Valley in south Asia is considered as one of the global "hot spots" in terms of urban air pollution. It is facing severe air quality problems as a result of rapid urbanization and land use change, socioeconomic transformation, and high population growth. In this paper, we present the first full year (February 2013–January 2014) analysis of simultaneous measurements of two short-lived climate forcers/pollutants (SLCF/P), i.e., ozone (O3) and equivalent black carbon (hereinafter noted as BC) and aerosol number concentration at Paknajol, in the city center of Kathmandu. The diurnal behavior of equivalent BC and aerosol number concentration indicated that local pollution sources represent the major contributions to air pollution in this city. In addition to photochemistry, the planetary boundary layer (PBL) and wind play important roles in determining O3 variability, as suggested by the analysis of seasonal changes of the diurnal cycles and the correlation with meteorological parameters and aerosol properties. Especially during pre-monsoon, high values of O3 were found during the afternoon/evening. This could be related to mixing and entrainment processes between upper residual layers and the PBL. The high O3 concentrations, in particular during pre-monsoon, appeared well related to the impact of major open vegetation fires occurring at the regional scale. On a synoptic-scale perspective, westerly and regional atmospheric circulations appeared to be especially conducive for the occurrence of the high BC and O3 values. The very high values of SLCF/P, detected during the whole measurement period, indicated persisting adverse air quality conditions, dangerous for the health of over 3 million residents of the Kathmandu Valley, and the environment. Consequently, all of this information may be useful for implementing control measures to mitigate the occurrence of acute pollution levels in the Kathmandu Valley and surrounding area.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 4
    Publication Date: 2020-03-12
    Description: The Kathmandu Valley in the Himalayan foothills, considered as one of the global "hot spots" for what concerns air pollution, is currently facing severe air quality problems due to rapid urbanization processes, dramatic land use changes, socioeconomic transformation and high population growth. In this work, we present the first full year (February 2013 - February 2014) analysis of simultaneous measurements of two short-lived climate forcers/pollutants (SLCF/P), i.e. ozone (O3) and equivalent black carbon (BC), and aerosol number concentration at Paknajol (27°43'4'' N, 85°18'32'' E, 1380 m a.s.l.), in the city center of Kathmandu. These observations were carried out in the framework of the SusKat-ABC (A Sustainable Atmosphere for the Kathmandu Valley - Atmospheric Brown Cloud) campaign in Nepal. The diurnal behavior of BC and aerosol number concentration indicated that local pollution sources represent the major contribution to air pollution in this city. In addition to photochemistry, the planetary boundary layer (PBL) dynamic plays an important role in determining O3 variability, as suggested by the analysis of seasonal changes of the diurnal cycles and the correlation with meteorological parameters and aerosol properties. Especially during pre-monsoon, high values of O3 were observed during the afternoon/evening. This could be related to mixing and entrainment processes between upper residual layers and the PBL. During this season, the high O3 appeared well related to the impact of major open vegetation fires occurring in Nepal. On a synoptic-scale perspective, westerly and regional atmospheric circulations appeared to be especially conducive for the occurrence of the high BC and O3 values. The very high values of the SLCF/P, detected during the whole measurement period, indicated persisting adverse air quality conditions, dangerous for the health of over 3 million residents of the Kathmandu Valley, and the environment. Consequently, all of this information may be useful for implementing control measures to mitigate the occurrence of acute pollution levels in the Kathmandu Valley and the surrounding area.
    Language: English
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  • 5
    Publication Date: 2020-03-12
    Language: English
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  • 6
    Publication Date: 2020-03-12
    Description: The Himalayas and the Tibetan Plateau region (HTP), despite being a remote and sparsely populated area, is regularly exposed to polluted air masses with significant amounts of aerosols including black carbon. These dark, light-absorbing particles are known to exert a great melting potential on mountain cryospheric reservoirs through albedo reduction and radiative forcing. This study combines ground-based and satellite remote sensing data to identify a severe aerosol pollution episode observed simultaneously in central Tibet and on the southern side of the Himalayas during 13–19 March 2009 (pre-monsoon). Trajectory calculations based on the high-resolution numerical weather prediction model COSMO are used to locate the source regions and study the mechanisms of pollution transport in the complex topography of the HTP. We detail how polluted air masses from an atmospheric brown cloud (ABC) over South Asia reach the Tibetan Plateau within a few days. Lifting and advection of polluted air masses over the great mountain range is enabled by a combination of synoptic-scale and local meteorological processes. During the days prior to the event, winds over the Indo-Gangetic Plain (IGP) are generally weak at lower levels, allowing for accumulation of pollutants and thus the formation of ABCs. The subsequent passing of synoptic-scale troughs leads to southwesterly flow in the middle troposphere over northern and central India, carrying the polluted air masses across the Himalayas. As the IGP is known to be a hotspot of ABCs, the cross-Himalayan transport of polluted air masses may have serious implications for the cryosphere in the HTP and impact climate on regional to global scales. Since the current study focuses on one particularly strong pollution episode, quantifying the frequency and magnitude of similar events in a climatological study is required to assess the total impact.
    Language: English
    Type: info:eu-repo/semantics/article
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  • 7
    Publication Date: 2020-03-12
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  • 8
    Publication Date: 2020-03-12
    Description: Our knowledge about ambient black carbon (BC) in the vast Himalayan region, a region vulnerable to impacts of global warming, is very limited due to unavailability of a long-term ambient monitoring. Here we present results from a continuous monitoring of ambient BC concentrations, with a new generation Aethalometer (AE33), over a three year period (January 2013- January 2016) at a semi-urban site in the highly polluted Kathmandu Valley in the foothills of the central Himalaya, one of the most polluted cities in the world. This is the longest time series of BC concentrations that have been monitored with AE33 (which uses the dual-spot technique for a real-time filter loading compensation) in highly polluted ambient environment. The measurements were carried out under the framework of project SusKat (Sustainable Atmosphere for the Kathmandu Valley). BC concentrations were found to be extremely high, especially in winter and the pre-monsoon period, with the hourly-averaged values often exceeding 50 μg/m3. BC concentrations showed a clear diurnal cycle with a prominent peak around 8-9 am and a second peak around 8-9 pm local time in all four seasons. Night-time BC was also fairly high. The diurnal cycle was driven by a combination of increased emissions from traffic, cooking activities, garbage burning, and lower mixing heights (˜200 m) and reduced horizontal ventilation in the mornings and evenings. BC concentrations showed significant seasonal variations - a maximum in winter season and minimum during the monsoon (rainy) season, with monthly average values in the range 5-30 μg/m3. An increase in emissions from the operation of over 100 brick kilns in winter and spring, and an increase in the use of small but numerous diesel power generators during hours with power cuts contributed significantly to ambient BC concentrations in the valley. Fractional contributions of biomass burning and fossil fuel combustion to BC was estimated based on a real-time method for loading effect compensation (using compensation parameter, k) implemented in the algorithm of the new dual-spot Aethalometer. This technique indicated that fossil fuel combustion (FF) and biomass burning (BB) contribute on average 70% and 30%, respectively, to ambient BC in the Kathmandu Valley. Relative contributions changed from season to season, e.g., BB fraction increased during November-December and March-April due to the seasonal increase in agro-residue burning and forest fires in the region, while FF fraction increased in winter due to increase in use of FF in brick factories and diesel generators. These measurements provided important information for understanding the properties of ambient BC and its impacts, especially on human health and climate, in the Kathmandu Valley and the surrounding foothills of the Himalayas.
    Language: English
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  • 9
    Publication Date: 2020-03-12
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  • 10
    Publication Date: 2020-03-12
    Description: A comprehensive regional assessment of emission sources is a major hindrance for a complete understanding of the air quality and for designing appropriate mitigation solutions in Nepal, a landlocked country in foothills of the Himalaya. This study attempts, for the first time, to develop a fine resolution (1km × 1km) present day emission inventory of Nepal with a higher tier approach using our understanding of the currently used technologies, energy consumption used in various energy sectors and its resultant emissions. We estimate present-day emissions of aerosols (BC, OC and PM2.5), trace gases (SO2, CO, NOX and VOC) and greenhouse gases (CO2, N2O and CH4) from non-open burning sources (residential, industry, transport, commercial) and open-burning sources (agriculture and municipal solid waste burning) for the base year 2013. We used methodologies published in literatures, and both primary and secondary data to estimate energy production and consumption in each sector and its sub-sector and associated emissions. Local practices and activity rates are explicitly accounted for energy consumption and dispersed often under-documented emission sources like brick manufacturing, diesel generator sets, mining, stone crushing, solid waste burning and diesel use in farms are considered. Apart from pyrogenic source of CH4 emissions, methanogenic and enteric fermentation sources are also accounted. Region-specific and newly measured country-specific emission factors are used for emission estimates. Activity based proxies are used for spatial and temporal distribution of emissions. Preliminary results suggest that 80% of national energy consumption is in residential sector followed by industry (8%) and transport (7%). More than 90% of the residential energy is supplied by biofuel which needs immediate attention to reduce emissions. Further, the emissions would be compared with other contemporary studies, regional and global datasets and used in the model simulations to understand impacts of air pollution on health and climate in Kathmandu Valley and Nepal. Future emissions are being developed based on different possible growth scenarios and policy interventions to mitigate emissions.
    Language: English
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