Ozone pollution in China: A review of concentrations, meteorological influences, chemical precursors, and effects

This overview paper highlights the successes of the Ozone Monitoring Instrument (OMI) on board the Aura satellite spanning a period of nearly 14 years. Data from OMI has been used in a wide range of applications and research resulting in many new findings. Due to its unprecedented spatial resolution, in combination with daily global coverage, OMI plays a unique role in measuring trace gases important for the ozone layer, air quality, and climate change. With the operational very fast delivery (VFD; direct readout) and near real-time (NRT) availability of the data, OMI also plays an important role in the development of operational services in the atmospheric chemistry domain.

/pdf/the-ozone-monitoring-instrument-overview-of-14-years-in-2ei1xxgz6l.pdf

The Ozone Monitoring Instrument: overview of 14 years in space

. Surface ozone data from the Chinese Ministry of Ecology
and Environment (MEE) network show sustained increases across the country
over the 2013–2019 period. Despite Phase 2 of the Clean Air Action Plan targeting
ozone pollution, ozone was higher in 2018–2019 than in previous years. The
mean summer 2013–2019 trend in maximum 8 h average (MDA8) ozone was 1.9 ppb a −1 ( p ) across China and 3.3 ppb a −1 ( p ) over the North China Plain (NCP). Fitting ozone to meteorological
variables with a multiple linear regression model shows that meteorology
played a significant but not dominant role in the 2013–2019 ozone trend,
contributing 0.70 ppb a −1 ( p ) across China and 1.4 ppb a −1 ( p=0.02 ) over the NCP. Rising June–July temperatures over the NCP
were the main meteorological driver, particularly in recent years
(2017–2019), and were associated with increased foehn winds. NCP data for
2017–2019 show a 15 % decrease in fine particulate matter (PM 2.5 )
that may be driving the continued anthropogenic increase in ozone, as well as
unmitigated emissions of volatile organic compounds (VOCs). VOC emission
reductions, as targeted by Phase 2 of the Chinese Clean Air Action Plan, are
needed to reverse the increase in ozone.

/pdf/increases-in-surface-ozone-pollution-in-china-from-2013-to-yvgy3z98sx.pdf

Increases in surface ozone pollution in China from 2013 to 2019: anthropogenic and meteorological influences

Changes in air quality related to the control of coronavirus in China: Implications for traffic and industrial emissions.

Determining effective strategies for mitigating surface ozone (O3) pollution requires knowledge of the relative ambient concentrations of its precursors, NOx, and VOCs. The space-based tropospheric column ratio of formaldehyde to NO2 (FNR) has been used as an indicator to identify NOx-limited versus NOx-saturated O3 formation regimes. Quantitative use of this indicator ratio is subject to three major uncertainties: (1) the split between NOx-limited and NOx-saturated conditions may shift in space and time, (2) the ratio of the vertically integrated column may not represent the near-surface environment, and (3) satellite products contain errors. We use the GEOS-Chem global chemical transport model to evaluate the quantitative utility of FNR observed from the Ozone Monitoring Instrument over three northern midlatitude source regions. We find that FNR in the model surface layer is a robust predictor of the simulated near-surface O3 production regime. Extending this surface-based predictor to a column-based FNR requires accounting for differences in the HCHO and NO2 vertical profiles. We compare four combinations of two OMI HCHO and NO2 retrievals with modeled FNR. The spatial and temporal correlations between the modeled and satellite-derived FNR vary with the choice of NO2 product, while the mean offset depends on the choice of HCHO product. Space-based FNR indicates that the spring transition to NOx-limited regimes has shifted at least a month earlier over major cities (e.g., New York, London, and Seoul) between 2005 and 2015. This increase in NOx sensitivity implies that NOx emission controls will improve O3 air quality more now than it would have a decade ago.

/pdf/evaluating-a-space-based-indicator-of-surface-ozone-no-x-voc-gtcffuee0h.pdf

Evaluating a Space-Based Indicator of Surface Ozone-NO x -VOC Sensitivity Over Midlatitude Source Regions and Application to Decadal Trends

. We present the new version (v14) of the BIRA-IASB algorithm for the retrieval of formaldehyde (H2CO) columns from spaceborne UV–visible sensors. Applied to OMI measurements from Aura and to GOME-2 measurements from MetOp-A and MetOp-B, this algorithm is used to produce global distributions of H2CO representative of mid-morning and early afternoon conditions. Its main features include (1) a new iterative DOAS scheme involving three fitting intervals to better account for the O2–O2 absorption, (2) the use of earthshine radiances averaged in the equatorial Pacific as reference spectra, and (3) a destriping correction and background normalisation resolved in the across-swath position. For the air mass factor calculation, a priori vertical profiles calculated by the IMAGES chemistry transport model at 09:30 and 13:30 LT are used. Although the resulting GOME-2 and OMI H2CO vertical columns are found to be highly correlated, some systematic differences are observed. Afternoon columns are generally larger than morning ones, especially in mid-latitude regions. In contrast, over tropical rainforests, morning H2CO columns significantly exceed those observed in the afternoon. These differences are discussed in terms of the H2CO column variation between mid-morning and early afternoon, using ground-based MAX-DOAS measurements available from seven stations in Europe, China and Africa. Validation results confirm the capacity of the combined satellite measurements to resolve diurnal variations in H2CO columns. Furthermore, vertical profiles derived from MAX-DOAS measurements in the Beijing area and in Bujumbura are used for a more detailed validation exercise. In both regions, we find an agreement better than 15 % when MAX-DOAS profiles are used as a priori for the satellite retrievals. Finally, regional trends in H2CO columns are estimated for the 2004–2014 period using SCIAMACHY and GOME-2 data for morning conditions, and OMI for early afternoon conditions. Consistent features are observed, such as an increase of the columns in India and central–eastern China, and a decrease in the eastern US and Europe. We find that the higher horizontal resolution of OMI combined with a better sampling and a more favourable illumination at midday allow for more significant trend estimates, especially over Europe and North America. Importantly, in some parts of the Amazonian forest, we observe with both time series a significant downward trend in H2CO columns, spatially correlated with areas affected by deforestation.

/pdf/diurnal-seasonal-and-long-term-variations-of-global-153n941wps.pdf

T. Vlemmix

Papers

Diurnal, seasonal and long-term variations of global formaldehyde columns inferred from combined OMI and GOME-2 observations