Observation and analysis of spatiotemporal characteristics of surface ozone and carbon monoxide at multiple sites in the Kathmandu Valley, Nepal

  • It was lower during the monsoon due to rainfall, which reduces open burning activities within the valley and in the surrounding regions and thus reduces sources of CO. The meteorology of the valley also played a key role in determining the CO mixing ratios. The wind is calm and easterly in the shallow mixing layer, with a mixing layer height (MLH) of about 250 m, during the night and early morning. The MLH slowly increases after sunrise and decreases in the afternoon. As a result, the westerly wind becomes active and reduces the mixing ratio during the daytime. Furthermore, there was evidence of an increase in the O-3 mixing ratios in the Kathmandu Valley as a result of emissions in the Indo-Gangetic Plain (IGP) region, particularly from biomass burning including agroresidue burning. A top-down estimate of the CO emission flux was made by using the CO mixing ratio and mixing layer height measured at Bode. The estimated annual CO flux at Bode was 4.9 mu g M-2 s(-1), which is 2-14 times higher than that in widely used emission inventoryIt was lower during the monsoon due to rainfall, which reduces open burning activities within the valley and in the surrounding regions and thus reduces sources of CO. The meteorology of the valley also played a key role in determining the CO mixing ratios. The wind is calm and easterly in the shallow mixing layer, with a mixing layer height (MLH) of about 250 m, during the night and early morning. The MLH slowly increases after sunrise and decreases in the afternoon. As a result, the westerly wind becomes active and reduces the mixing ratio during the daytime. Furthermore, there was evidence of an increase in the O-3 mixing ratios in the Kathmandu Valley as a result of emissions in the Indo-Gangetic Plain (IGP) region, particularly from biomass burning including agroresidue burning. A top-down estimate of the CO emission flux was made by using the CO mixing ratio and mixing layer height measured at Bode. The estimated annual CO flux at Bode was 4.9 mu g M-2 s(-1), which is 2-14 times higher than that in widely used emission inventory databases (EDGAR HTAP, REAS and INTEX-B). This difference in CO flux between Bode and other emission databases likely arises from large uncertainties in both the top-down and bottom-up approaches to estimating the emission flux. The O-3 mixing ratio was found to be highest during the premonsoon season at all sites, while the timing of the seasonal minimum varied across the sites. The daily maximum 8 h average O-3 exceeded the WHO recommended guideline of 50 ppb on more days at the hilltop station of Nagarkot (159 out of 357 days) than at the urban valley bottom sites of Paknajol (132 out of 354 days) and Bode (102 out of 353 days), presumably due to the influence of free-tropospheric air at the high-altitude site (as also indicated by Putero et al., 2015, for the Paknajol site in the Kathmandu Valley) as well as to titration of O-3 by fresh NOx emissions near the urban sites. More than 78 % of the exceedance days were during the premonsoon period at all sites. The high O-3 mixing ratio observed during the premonsoon period is of a concern for human health and ecosystems, including agroecosystems in the Kathmandu Valley and surrounding regions.show moreshow less

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Author details:Khadak Singh Mahata, Maheswar RupakhetiORCiD, Arnico Kumar Panday, Piyush Bhardwaj, Manish Naja, Ashish Singh, Andrea Mues, Paolo CristofanelliORCiD, Deepak Pudasainee, Paolo Bonasoni, Mark G. LawrenceORCiD
DOI:https://doi.org/10.5194/acp-18-14113-2018
ISSN:1680-7316
ISSN:1680-7324
Title of parent work (English):Atmosheric chemistry and physics
Publisher:Copernicus
Place of publishing:Göttingen
Publication type:Article
Language:English
Year of first publication:2018
Completion year:2018
Release date:2021/09/13
Volume:18
Issue:19
Number of pages:20
First page:14113
Last Page:14132
Funding institution:German Ministry of Education and Research (BMBF)Federal Ministry of Education & Research (BMBF); Brandenburg State Ministry of Science, Research and Culture (MWFK); ICIMOD; government of Afghanistan; government of Australia; government of Austria; government of Bangladesh; government of Bhutan; government of China; government of India; government of Myanmar; government of Nepal; government of Norway; government of Pakistan; government of Switzerland; government of United Kingdom; Government of Sweden
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Geowissenschaften
DDC classification:5 Naturwissenschaften und Mathematik / 55 Geowissenschaften, Geologie / 550 Geowissenschaften
Peer review:Referiert
Publishing method:Open Access / Gold Open-Access
DOAJ gelistet
External remark:Zweitveröffentlichung in der Schriftenreihe Postprints der Universität Potsdam : Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe ; 848