Elevated ground-level ozone (O3), which is an important aspect of air quality related to public health, has been causing increasing concern. This study investigated the spatiotemporal distribution of ground-level O3 concentrations in China using a dataset from the Chinese national air quality monitoring network during 2013–2015. This research analyzed the diurnal, monthly and yearly variation of O3 concentrations in both sparsely and densely populated regions. In particular, 6 major Chinese cities were selected to allow a discussion of variations in O3 levels in detail, Beijing, Chengdu, Guangzhou, Lanzhou, Shanghai, and Urumchi, located on both sides of the Heihe-Tengchong line. Data showed that the nationwide 3-year MDA8 of ground-level O3 was 80.26 μg/m3. Ground-level O3 concentrations exhibited monthly variability peaking in summer and reaching the lowest levels in winter. The diurnal cycle reached a minimum in morning and peaked in the afternoon. Yearly average O3 MDA8 concentrations in Beijing, Chengdu, Lanzhou, and Shanghai in 2015 increased 12%, 25%, 34%, 22%, respectively, when compared with those in 2013. Compared with World Health Organization O3 guidelines, Beijing, Chengdu, Guangzhou, and Shanghai suffered O3 pollution in excess of the 8-hour O3 standard for more than 30% of the days in 2013 to 2015.
Abstract. Ground-level ozone (O3) pollution has been steadily
getting worse in most parts of eastern China during the past 5 years. The
non-linearity of O3 formation with its precursors like nitrogen oxides
(NOx= NO + NO2) and volatile organic compounds (VOCs) are
complicating effective O3 abatement plans. The diagnosis from
space-based observations, i.e. the ratio of formaldehyde (HCHO) columns to
tropospheric NO2 columns (HCHO / NO2), has previously been proved to
be highly consistent with our current understanding of surface O3
chemistry. HCHO / NO2 ratio thresholds distinguishing O3 formation
sensitivity depend on regions and O3 chemistry interactions with
aerosol. To shed more light on the current O3 formation sensitivity
over China, we have derived HCHO / NO2 ratio thresholds by directly
connecting satellite-based HCHO / NO2 observations and ground-based
O3 measurements over the major Chinese cities in this study. We find
that a VOC-limited regime occurs for HCHO / NO2 < 2.3, and
a NOx-limited regime occurs for HCHO / NO2 > 4.2. The
HCHO / NO2 between 2.3 and 4.2 reflects the transition between the two
regimes. Our method shows that the O3 formation sensitivity tends to be
VOC-limited over urban areas and NOx-limited over rural and remote
areas in China. We find that there is a shift in some cities from the
VOC-limited regime to the transitional regime that is associated with a rapid drop
in anthropogenic NOx emissions, owing to the widely applied rigorous
emission control strategies between 2016 and 2019. This detected spatial
expansion of the transitional regime is supported by rising surface O3
concentrations. The enhanced O3 concentrations in urban areas during
the COVID-19 lockdown in China indicate that a protocol with simultaneous
anthropogenic NOx emissions and VOC emissions controls is essential for
O3 abatement plans.
Air pollution has aroused significant public concern in China, therefore, long-term air-quality data with high temporal and spatial resolution are needed to understand the variations of air pollution in China. However, the yearly variations with high spatial resolution of air quality and six air pollutants are still unknown for China until now. Therefore, in this paper, we analyze the spatial and temporal variations of air quality and six air pollutants in 366 cities across mainland China during 2015–2017 for the first time to the best of our knowledge. The results indicate that the annual mean mass concentrations of PM2.5, PM10, SO2, and CO all decreased year by year during 2015–2017. However, the annual mean NO2 concentrations were almost unchanged, while the annual mean O3 concentrations increased year by year. Anthropogenic factors were mainly responsible for the variations of air quality. Further analysis suggested that PM2.5 and PM10 were the main factors influencing air quality, while NO2 played an important role in the formation of PM2.5 and O3. These findings can provide a theoretical basis for the formulation of future air-pollution control policy in China.
Abstract. Ground-level ozone (O3) pollution has been steadily getting worse in most part of eastern China during the past five years. The non-linearity of O3 formation with its precursors like nitrogen oxides (NOx = NO + NO2) and volatile organic compounds (VOCs) are complicating effective O3 abatement plans. The diagnosis from space-based observations, the ratio of formaldehyde (HCHO) columns to tropospheric NO2 columns (HCHO / NO2), has previously been proved to be highly consistent with our current understanding of surface O3 chemistry. HCHO / NO2 ratio thresholds distinguishing O3 formation sensitivity depend on regions and O3 chemistry interactions with aerosol. To shed more light on current the O3 formation sensitivity over China, we have derived HCHO / NO2 ratio thresholds by directly connecting satellite-based HCHO / NO2 observations and ground-based O3 measurements over the major Chinese cities in this study. We find that a VOC-limited regime occurs for HCHO / NO2 4.2. The HCHO / NO2 between 2.3 and 4.2 reflects the transition between the two regimes. Our method shows that the O3 formation sensitivity tends to be VOC-limited over urban areas and NOx-limited over rural and remote areas in China. We find that there is a shift in some cities from the VOC-limited to the transitional regime that is associated with a rapid drop of anthropogenic NOx emissions owing to the widely-applied rigorous emission control strategies between 2016 and 2019. This detected spatial expansion of the transitional regime is supported by rising surface O3 concentrations. The enhanced O3 concentrations in urban areas during the COVID-19 lockdown in China indicate that a protocol with simultaneous anthropogenic NOx emissions and VOC emissions controls is essential for O3 abatement plans.
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