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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 22 Jun 2020

Submitted as: research article | 22 Jun 2020

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This preprint is currently under review for the journal ACP.

Retrieving tropospheric NO2 vertical column densities around the city of Beijing and estimating NOx emissions based on carMAX-DOAS measurements

Xinghong Cheng1, Jianzhong Ma1, Junli Jin2, Junrang Guo1, Yuelin Liu3, Jida Peng4, Xiaodan Ma5, Minglong Qian6, Qiang Xia6, and Peng Yan2 Xinghong Cheng et al.
  • 1State Key Lab of Severe Weather & Key Laboratory for Atmospheric Chemistry, Chinese Academy of Meteorological Sciences, Beijing 100081, China
  • 2CMA Meteorological Observation Centre, Beijing 100081, China
  • 3College of Architecture and Environment, Sichuan University, Chengdu 610065, China
  • 4Meteorological Institute of Fujian, Fuzhou 350001,China
  • 5Nanjing University of Information Science and Technology, Nanjing 210044, China
  • 6China National Huayun Technology Development Corporation, Beijing 100081, China

Abstract. We carried out 19 city-circle-around car MAX-DOAS experiments on the 6th Ring Road of Beijing in January, September, and October 2014. The tropospheric vertical column densities (VCDs) of NO2 were retrieved from measured spectra by the Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique and used to estimate the emissions of NOx (≡ NO + NO2) from urban Beijing during the experimental periods. The offline LAPS-WRF-CMAQ model system was used to simulate the wind fields by assimilation of observational data and calculate the NO2-to-NOx concentration ratios, both of which are also needed for the estimation of NOx emissions. The NOX emissions in urban Beijing for the different seasons derived from the car MAX-DOAS measurements in this study were compared to the multi-resolution emission inventory in China for 2012 (MEIC 2012). Our car MAX-DOAS measurement results showed higher NO2 VCD in January than in the other two months and typically larger NO2 VCD at the southern parts of the 6th Ring Road than at the northern parts. The wind field had obvious impacts on the spatial distribution of NO2 VCD, with the mean NO2 VCD along the 6th Ring Road typically being higher under the south wind than under the north wind. In addition to the seasonal difference, the journey-to-journey variations of estimated NOx emissions rates (ENOx) were large even within the same month, mainly due to uncertainties in the calculations of wind speed, the ratio of NO2 and NOx concentration, and the decay rate of NOx from the emission sources to the measured positions under different meteorological conditions. The ranges of ENOx during the heating and non-heating periods were 28.7 × 1025 to 60.0 × 1025 molecules s−1 and 7.7 × 1025 to 24.8 × 1025 molecules s−1, respectively. The average ENOx values in the heating and non-heating periods were 43.0 × 1025 molecules s−1 and 13.9 × 1025 molecules s−1, respectively. The uncertainty range of ENOx was 16.4–33.2 %. The monthly emission rates from MEIC 2012 are found to be lower than the estimated ENOX, particularly in January. Our results provide important information and datasets for the validation of satellite products and also show how car MAX-DOAS measurements can be used effectively for dynamic monitoring and updating of the NOx emissions from megacities such as Beijing.

Xinghong Cheng et al.

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Xinghong Cheng et al.

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Short summary
We carried out 19 city-circle-around Car MAX-DOAS experiments on the 6th Ring Road of Beijing in Jan., Sep., and Oct. 2014. The tropospheric VCDs of NO2 are retrieved and their temporal and spatial distributions are investigated. Then the NOx emission rates in urban Beijing are estimated using the measured NO2 VCDs together with the refined wind fields, NO2 to NOx ratios, and NO2 lifetimes simulated by the LAPS-WRF-CMAQ model system, and results are compared with the MEIC inventory 2012.
We carried out 19 city-circle-around Car MAX-DOAS experiments on the 6th Ring Road of Beijing in...