Spatial and temporal variability of ozone sensitivity over China observed from the Ozone Monitoring Instrument

Abstract

Surface ozone (O 3 ) air pollution in populated regions has been attributed to emissions of nitrogen oxides (NO + NO 2 = NO x ) and reactive volatile organic compounds (VOCs). These constituents react with hydrogen oxide radicals (OH + HO 2 = HO x ) in the presence of sunlight and heat to produce O 3 . The question of whether to reduce NO x emissions, VOC emissions, or both is complicated by spatially and temporally heterogeneous ozone-NO x -VOC sensitivity. This study characterizes spatial and temporal variations in O 3 sensitivity by analyzing the ratio of formaldehyde (HCHO, a marker of VOCs) to nitrogen dioxide (NO 2 ), a metric known as the formaldehyde nitrogen ratio (FNR). Level 3 gridded retrievals from the Ozone Monitoring Instrument (OMI) aboard the NASA Aura satellite were used to calculate FNR, with our analysis focusing on China. Based on previous studies, we take FNR < 1.0 as indicating VOC-limited regimes, FNR > 2.0 as indicating NO x -limited regime, and FNR between 1.0 and 2.0 as indicating transitional regime (where either NO x reductions or VOC reductions would be expected to reduce O 3 ). We find that the transitional regime is widespread over the North China Plain (NCP), the Yangtze River Delta, and the Pearl River Delta during the ozone season (defined as having near-surface air temperatures >20°C at the early afternoon OMI overpass time). Outside of these regions, the NO x -limited regime is dominant. Because HCHO and NO 2 have distinct seasonal patterns, FNR also has a pronounced seasonality, consistent with the seasonal cycle of surface O 3 . Examining trends from 2005 to 2013 indicates rapid growth in NO 2 , especially over less-developed areas where O 3 photochemistry is NO x limited. Over this time period, HCHO decreased in southern China, where VOC emissions are dominated by biogenic sources, but increased slightly over the NCP, where VOC emissions are dominated by anthropogenic sources. A linear regression approach suggests that most of China (70% of grid cells) will be characterized by a transitional regime during the O 3 season by 2030. However, in megacities such as Guangzhou, Shanghai, and Beijing, NO 2 has decreased such that the chemical regime has shifted from VOC limited in 2005 to transitional in 2013.

The Ozone Monitoring Instrument: overview of 14 years in space

“…Duncan et al (2010) used the ratio of OMI HCHO to NO 2 columns to show that the chemical sensitivity of ozone formation was becoming more sensitive to NO x levels in US cities, even cities that were typically considered to be more sensitive to VOCs (e.g., Los Angeles), as a result of substantial reductions in NO x emissions. Over China, Jin and Holloway (2015) found a complex result owing to significant spatial heterogeneity of NO x and VOC emission changes during the OMI record.…”

Spatiotemporal Variations in Satellite-Based Formaldehyde (HCHO) in the Beijing-Tianjin-Hebei Region in China from 2005 to 2015

“…Anthropogenic emissions are a major source of VOCs in China, and Beijing-Tianjin-Hebei is an important industrial zone in the north. Thus, the observed HCHO VCDs could have possibly originated from anthropogenic sources [6]. Meanwhile, HCHO is mainly concentrated within the more densely populated parts of Beijing-Tianjin-Hebei, in which emissions from industries and vehicles cannot be neglected.…”

“…Fu et al proposed a linear function relating HCHO and VOCs and analyzed the distribution of HCHO in South and East China through a continuous 6-year record (1996)(1997)(1998)(1999)(2000)(2001) of GOME satellite measurements [4]. Jin et al and Souri et al also studied the distribution of HCHO throughout China, but only as a component of a larger research experiment [6,20]. However, more thorough investigations focused on Beijing-Tianjin-Hebei are still required urgently.…”

Urban Emissions and Regional Air Quality in India

“…Many studies on Indian air quality rely on satellite observations as a result of these biases and limited availability of ground-based monitor data across India, including NO 2 from OMI aboard the Aura satellite [Lamsal et al, 2010;Ghude et al, 2013]. Satellite observations from OMI and other instruments have been previously used to evaluate emissions and surface concentrations [Lamsal et al, 2010;Lu and Streets, 2012;Lu et al, 2013;Streets et al, 2013], observe trends in air quality [Lamsal et al, 2013[Lamsal et al, , 2015Duncan et al, 2015;Krotkov et al, 2015], evaluate AOD for dust or anthropogenic pollution [King et al, 2003;Isakov et al, 2007;Zhao et al, 2010], and estimate NO X to VOC ratios in assessing O 3 regimes [Jin and Holloway, 2015]. Limitations of satellite observations include temporal availability (i.e.…”