Abstract
A series of strict emission control measures were implemented in Beijing and surrounding regions to ensure good air quality during the 2014 Asia-Pacific Economic Cooperation (APEC) summit and 2015 Grand Military Parade (Parade), which led to blue sky days during these two events commonly referred to as “APEC Blue” and “Parade Blue”. Here we calculated Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) and Ozone Monitoring Instrument (OMI) NO2 and HCHO results based on well known DOAS trace gas fitting algorithm and WRF-Chem model (with measured climatology parameter and newest emission inventor) simulated trace gases profiles. We found the NO2 columns abruptly decreased both Parade (43%) and APEC (21%) compared with the periods before these two events. The back-trajectory cluster analysis and the potential source contribution function (PSCF) proved regional transport from southern peripheral cities plays a key role in pollutants observed at Beijing. The diminishing transport contribution from southern air mass during Parade manifests the real effect of emission control measures on NO2 pollution. Based on the ratios of HCHO over NO2 we found there were not only limited the NO2 pollutant but also suppress the O3 contaminant during Parade, while O3 increased during the APEC.
Highlights
Atmospheric pollution has become a serious menace to public health all over the world, especially in China[1,2]
To explicitly probe the impact of emission and transmission perturbation on altering the air quality, we propose to use the MAX-DOAS and Ozone Monitoring Instrument (OMI) satellite observations to retrieve the NO2 vertical column densities (VCDs), and combine potential source contribution function (PSCF) method to analyze the NO2 potential source at Beijing urban area (Fig. S1, 40°N, 116°22ʹ4 8′′E) during Parade and Asia-Pacific Economic Cooperation (APEC) periods in this study
In order to evaluate the impact of emission control policy on air quality during Parade and APEC, three episodes are separately defined in this study: 1st episodes is defined as the period of Parade, in which the strict air quality policies were implemented at a regional scale; 2nd and 3rd episodes are defined as the “pre-Parade” from August 5th to 19th and the “post-Parade” from September 4th to 21st
Summary
Atmospheric pollution has become a serious menace to public health all over the world, especially in China[1,2]. The previous study had demonstrated that HCHO and NO2 from the OMI serve as appropriate proxies for in situ observations of total reactive nitrogen (NOy) and VOC in polluted environments, just like Beijing, and their ratio is an appropriate indicator to examine the chemical sensitivity of local ozone production (PO3)[20,21,22]. They found that OMI tropospheric HCHO/NO2 Ratio (hereafter refer to as “Ratio”) 2 represents NOx-limited conditions. When ratio is between 1 and 2 indicates that a transition regime (mixed VOC-NOx-limited regime) where the instantaneous PO3 can be changed by both VOC and NOx emissions[21]
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