TY  - JOUR
A1  - Mahata, Khadak Singh
A1  - Rupakheti, Maheswar
A1  - Panday, Arnico Kumar
A1  - Bhardwaj, Piyush
A1  - Naja, Manish
A1  - Singh, Ashish
A1  - Mues, Andrea
A1  - Cristofanelli, Paolo
A1  - Pudasainee, Deepak
A1  - Bonasoni, Paolo
A1  - Lawrence, Mark
T1  - Observation and analysis of spatiotemporal characteristics of surface ozone and carbon monoxide at multiple sites in the Kathmandu Valley, Nepal
JF  - Atmosheric chemistry and physics
N2  - 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 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.
Y1  - 2018
U6  - https://doi.org/10.5194/acp-18-14113-2018
SN  - 1680-7316
SN  - 1680-7324
VL  - 18
IS  - 19
SP  - 14113
EP  - 14132
PB  - Copernicus
CY  - Göttingen
ER  -