Oxidant (O₃ + NO₂) production processes and formation regimes in Beijing

Abstract

[1] For CareBeijing-2006, two sites were established in urban and suburban regions of Beijing in summer 2006. Observations of O 3 and its precursors together with meteorological parameters at both sites are presented. Gross ozone production rate P(O 3 ) and sensitivity to nitric oxides (NO x ) and volatile organic compounds (VOCs) were investigated using an observation-based photochemical box model (OBM). P(O 3 ) varied from nearly zero to 120 and 50 ppb h −1 for urban and suburban sites, respectively. These rates were greater than the accumulation rates of the observed oxidant (O 3 + NO 2 ) concentrations. The O 3 episodes typically appeared under southerly wind conditions with high P(O 3 ), especially at the urban site. Sensitivity studies with and without measured nitrous acid (HONO) as a model constraint suggested that the estimated P(O 3 ) at both sites was strongly enhanced by radical production from HONO photolysis. Both NO x -and VOC-sensitive chemistries existed over time scales from hours to days at the two sites. The variation in O 3 -sensitive chemistry was relatively well explained by the ratio of the average daytime total VOC reactivity (k TVOC ) to NO, with the transition chemistry corresponding to a k TVOC /NO value of 2-4 s. Pronounced diurnal variations in the O 3 production regime were found. In the morning, conditions were always strongly VOC-limited, while in the afternoon, conditions were variable for different days and different sites. The model-calculated results were tested by measurements of H 2 O 2 , HNO 3 , total OH reactivity, and HO x radicals. The OBM was generally capable of correctly simulating the levels of P(O 3 ), although it might tend to overpredict the VOC-sensitive chemistry.

PM1 Chemical Characterization during the ACU15 Campaign, South of Mexico City

“…NO and BC seems to peak one hour before, which probably is explained by the public transport station located approximately 300 m from the site, where activities start earlier. On the other hand, the SV-OOA factor has a maximum similar to the "total oxidant" Ox (Ox = O3 + NO2), which is a proxy for the "real" photochemical production of O3 because it takes into account the rapid interconversion between NO2 and O3 [41]. This similarity is indicative of fresh production of secondary organic aerosol.…”

Nighttime observation and chemistry of HO<sub>x</sub> in the Pearl River Delta and Beijing in summer 2006

“…In PRD, the measurement site Backgarden (BG) was located in a rural environment influenced by pollution from the megacity of Guangzhou, while the other site was in the suburban area Yufa (YF) in the vicinity of Beijing. Almost identical instrumentation was used at the two sites to characterize the processes of trace gas removal, photochemical ozone production and aerosol formation Lu et al, 2013Lu et al, , 2012Lu et al, , 2010aLi et al, 2012;Lou et al, 2010;Xiao et al, 2009). Trace gases (HO x ,O 3 , NO x , CO, C 2 -C 12 hydrocarbons, HONO), photolysis frequencies, and meteorological parameters (temperature, pressure, relative humdity) were measured.…”

Ozone production in summer in the megacities of Tianjin and Shanghai, China: a comparative study

“…In the NCP region, most observations and analysis were performed at regional background sites or in the megacity of Beijing (e.g. Gao et al, 2005;Lin et al, 2008Lin et al, , 2009Lin et al, , 2011Tang et al, 2010;Lu et al, 2010;Xu et al, 2011a). In preparation for the 2008 Olympics, the relocation of old industrial facilities away from Beijing and other stringent emission restrictions were implemented to mitigate local air pollution.…”