Maite Bauwens

Substantial Underestimation of Post-Harvest Burning Emissions in the North China Plain Revealed by Multi-Species Space Observations

The large-scale burning of crop residues in the North China Plain (NCP), one of the most densely populated world regions, was recently recognized to cause severe air pollution and harmful health effects. A reliable quantification of the magnitude of these fires is needed to assess regional air quality. Here, we use an eight-year record (2005–2012) of formaldehyde measurements from space to constrain the emissions of volatile organic compounds (VOCs) in this region. Using inverse modelling, we derive that satellite-based post-harvest burning fluxes are, on average, at least a factor of 2 higher than state-of-the-art bottom-up statistical estimates, although with significant interannual variability. Crop burning is calculated to cause important increases in surface ozone (+7%) and fine aerosol concentrations (+18%) in the North China Plain in June. The impact of crop fires is also found in satellite observations of other species, glyoxal, nitrogen dioxide and methanol, and we show that those measurements validate the magnitude of the top-down fluxes. Our study indicates that the top-down crop burning fluxes of VOCs in June exceed by almost a factor of 2 the combined emissions from other anthropogenic activities in this region, underscoring the need for targeted actions towards changes in agricultural management practices.

Top‐Down CO Emissions Based On IASI Observations and Hemispheric Constraints on OH Levels

Assessments of carbon monoxide emissions through inverse modeling are dependent on the modeled abundance of the hydroxyl radical (OH) which controls both the primary sink of CO and its photochemical source through hydrocarbon oxidation. However, most chemistry transport models (CTMs) fall short of reproducing constraints on hemispherically averaged OH levels derived from methylchloroform (MCF) observations. Here we construct five different OH fields compatible with MCF-based analyses, and we prescribe those fields in a global CTM to infer CO fluxes based on Infrared Atmospheric Sounding Interferometer (IASI) CO columns. Each OH field leads to a different set of optimized emissions. Comparisons with independent data (surface, ground-based remotely sensed, aircraft) indicate that the inversion adopting the lowest average OH level in the Northern Hemisphere (7.8 × 105 molec cm−3, ∼18% lower than the best estimate based on MCF measurements) provides the best overall agreement with all tested observation data sets.

Sources and Long-Term Trends of Ozone Precursors to Asian Pollution

Due to its fast economic development, China’s emissions are in the spotlight of efforts to mitigate climate change and improve regional and city-scale air quality. Despite growing efforts to better quantify China’s emissions, the current estimates are often poor or inadequate. Bottom-up inventories are generally based on sectoral statistical information and therefore rely strongly on the accuracy of the input data. Complementary to bottom-up methodologies, inverse modeling of fluxes has the potential to improve those estimates through the use of atmospheric observations of trace gas compounds. Here we present comparisons of key pollutant emissions from different bottom-up inventories, and perform 20-year model simulations of the atmospheric composition over China using either the EDGARv4.2 or the MACCity bottom-up emission databases. The skill of the model to capture the observed variability and trends is assessed through comparisons with satellite NO2 observations retrieved from GOME, SCIAMACHY and OMI sensors through 1997–2008 and HCHO columns observed by OMI over 2005–2010. Next, we use a decade (2005–2014) of OMI HCHO columns to constrain the VOC emissions over China in a flux inversion framework built on the IMAGESv2 chemistry-transport model, and adjust the emissions of VOC precursors of HCHO in the model in order to reduce the discrepancy between the model predictions and the HCHO observations. The interannual and seasonal variability of the resulting top-down VOC fluxes (anthropogenic, pyrogenic and biogenic) is presented and confronted to past studies.

Impact of Short‐Term Climate Variability on Volatile Organic Compounds Emissions Assessed Using OMI Satellite Formaldehyde Observations

A major feedback between climate and atmospheric chemistry lies in the meteorological dependence of the emissions of biogenic volatile organic compounds (BVOCs), precursors of important climate forcers, aerosols, and ozone. Whereas the short‐term response of BVOC emissions to meteorological drivers is fairly well simulated by current emission models, it is yet unclear whether models can faithfully predict their response to climate change, given the scarcity of long observation records of BVOC fluxes. Here we take advantage of the high yield of formaldehyde (HCHO) in the oxidation of VOCs and use a long‐term spaceborne record of HCHO observations in combination with model simulations to show that (i) HCHO interannual variability is primarily driven by climate through its impacts on photochemistry, vegetation fire occurrence, and above all, biogenic emissions and (ii) the HCHO record validates the interannual variability of biogenic emissions calculated by the state‐of‐the‐art Model of Emissions of Gases and Aerosols from Nature (MEGAN) emission model in vegetated regions.