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Discussion papers
https://doi.org/10.5194/acp-2019-781
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-781
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 Nov 2019

Submitted as: research article | 04 Nov 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Evaluation of nitrogen oxides sources and sinks and ozone production in Colombia and surrounding areas

Johannes G. M. Barten1, Laurens N. Ganzeveld1, Auke J. Visser1, Rodrigo Jiménez2, and Maarten C. Krol1,3 Johannes G. M. Barten et al.
  • 1Wageningen University, Meteorology and Air Quality Section, Wageningen, the Netherlands
  • 2Department of Chemical and Environmental Engineering, Air Quality Research Group, Universidad Nacional de Colombia – Bogotá, Colombia
  • 3Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, the Netherlands

Abstract. In Colombia, industrialization and a shift towards intensified agriculture have led to increased emissions of air pollutants. However, the baseline state of air quality in Colombia is relatively unknown. In this study we aim to assess the baseline state of air quality in Colombia with a focus on the spatial and temporal variability in emissions and atmospheric burden of nitrogen oxides (NOx = NO + NO2) and evaluate surface NOx, ozone (O3) and carbon monoxide (CO) mixing ratios. We quantify the magnitude and spatial distribution of the four major NOx sources (lightning, anthropogenic activities, soil biogenic emissions and biomass burning), by integrating global NOx emission inventories into the mesoscale meteorology and atmospheric chemistry model WRF-Chem. The comparison with in situ measurements is bound to urban areas whereas the use of remote sensing data allows to also evaluate air quality in remote regions. WRF-Chem was set up for a domain centered over Colombia with a similar resolution as OMI observed NO2 vertical columns as well as the EDGAR anthropogenic emission inventory, both providing information on a ~20 km resolution. However, this apparently poses a challenge regarding comparison with these urban observations. Air mass factors were recalculated based on the vertical distribution of NO2 within WRF-Chem, with respect to the coarse (1° x 1°) a priori profiles. The main reason for recalculation is a more consistent satellite-model comparison but it also reduced the mean bias. WRF-Chem was, on average, able to provide good estimates for tropospheric NO2 columns with an averaged difference of 0.02 x 1015 molecules cm-2, which is < 5 % of the mean column. However, the simulated NO2 columns are overestimated in regions with abundant modeled lightning emissions and underestimated in regions where biomass burning emissions dominate in the model. This result reflects the high contribution by lightning emissions (1258 Gg N yr-1) and the low contribution by biomass burning emissions (104 Gg N yr-1) to total NOx emissions within the WRF-Chem domain. WRF-Chem was unable to capture NOx and CO urban pollutant mixing ratios, both in timing and magnitude. Yet, WRF-Chem was able to simulate the urban diurnal cycle of O3 satisfactory but with a systematic overestimation of 10 ppb due to the equally large underestimation of NO mixing ratios and, consequently, titration. This indicates that these city environments are in the NOx saturated regime with frequent O3 titration. We also applied an online meteorology-chemistry single column model (SCM) to evaluate how enhanced emissions and different representation of advection and mixing conditions could explain an improved representation of the observed O3 and NOx diurnal cycles. The SCM appears to indeed better represent the observed diurnal cycle of urban pollutant mixing ratios. But, interestingly, this result did not require an enhancement in the emissions, indicating that the role of boundary layer dynamics and advection should be considered besides the use of high-resolution models and emissions inventories to realistically simulate urban air quality. Results obtained in this study provide insight in the magnitude, distribution and temporal evolution of different sources of pollution in Colombia and its surrounding territories. This study not only identifies different source regions, but also shows the interannual variability of these sources during the last one and a half decade using satellite data. Furthermore, this study shows that relatively coarse anthropogenic emission inventories can give reasonable results regarding the diurnal cycle of urban pollutant mixing ratios with a careful consideration of advection and mixing conditions. It serves as a base to assess scenarios of future air quality in Colombia, or similar regions with distinct contrasting emission regimes and a limited air quality monitoring network, as a function of further industrialization and land use changes.

Johannes G. M. Barten et al.
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Short summary
We present the baseline state of air quality in Colombia combining satellite and urban air pollution measurements with a meteorology/air quality model. We found four distinctly different emission regimes. The simulated pollution levels compare well with satellite data but the comparison also indicates misrepresentation of prescribed fire emissions & simulated lightning emissions. Comparison of urban measurements requires careful consideration of (nocturnal) boundary layer dynamics and advection.
We present the baseline state of air quality in Colombia combining satellite and urban air...
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