Measurements of traffic dominated pollutant emissions in a Chinese megacity

Abstract

Abstract. Direct measurements of NOx, CO and aromatic VOC (benzene, toluene, C2-benzenes and C3-benzenes) flux were made for a central area of Beijing using the eddy covariance technique. Measurements were made during two intensive field campaigns in central Beijing as part of the Air Pollution and Human Health (APHH) project, the first in November–December 2016 and the second during May–June 2017, to contrast winter and summertime emission rates. There was little difference in the magnitude of NOx flux between the two seasons (mean NOx flux was 4.41 mg m−2 h−1 in the winter compared to 3.55 mg m−2 h−1 in the summer). CO showed greater seasonal variation with mean CO flux in the winter campaign (34.7 mg m−2 h−1) being over twice that of the summer campaign (15.2 mg m−2 h−1). Larger emissions of aromatic VOCs in summer were attributed to increased evaporation due to higher temperatures. The largest fluxes in NOx and CO generally occurred during the morning and evening rush hour periods indicating a major traffic source with high midday emissions of CO indicating an additional influence from cooking fuel. Measured NOx and CO fluxes were then compared to the MEIC 2013 emissions inventory which was found to significantly overestimate emissions for this region, providing evidence that proxy-based emissions inventories have positive biases in urban centres. This first set of pollutant fluxes measured in Beijing provides an important benchmark of emissions from the city which can help to inform and evaluate current emissions inventories.

Evaluating the sensitivity of radical chemistry and ozone formation to ambient VOCs and NO<sub>x</sub> in Beijing

“…Despite the close proximity of the measurement site to the heavily trafficked Jingzang highway in Beijing, mixing ratios of NO, which were elevated during the morning hours, often dropped below 500 pptv during the afternoon. The daytime emissions of NOx that were recorded during the project displayed a rapid increase at 05:00 and then remained reasonably constant throughout the day, with a mean flux value of 4.6 mg m -2 hr -1 , before dropping again at 17:00 (Squires et al, 2020).…”

Sources of non-methane hydrocarbons in surface air in Delhi, India

“…The setup and calibration procedures were identical to those described by Squires et al (2020). 49 PTR-QiTOF-MS (Ionicon Analytik, Innsbruck) measurements were made from 26/05/2018 to 09/06/2018 in the premonsoon campaign and from 04/10/2018 to 23/11/2018 in the post-monsoon campaign. For the pre-monsoon and post-monsoon campaign up until 05/11/2018 the sample inlet was positioned 5 m above the ground adjacent to the inlet used for GC measurements.…”

Review of ‘The promotion effect of nitrous acid on aerosol formation in wintertime Beijing: possible contribution of traffic-related emission’ by Liu et al

“…Why wasn't hourly EI used, and did you consider your measured NOx concentrations, as the diurnal variation in NOx would be important? Please clarify in more detail how the Evehicle was calculated Especially as emission inventories can have significant bias (See for example very recent work for Beijing by Squires et al, 2020).…”