Abstract
Abstract. Global surface emissions of nitrogen oxides (NOx) over a 10-year period (2005–2014) are estimated from an assimilation of multiple satellite data sets: tropospheric NO2 columns from Ozone Monitoring Instrument (OMI), Global Ozone Monitoring Experiment-2 (GOME-2), and Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY), O3 profiles from Tropospheric Emission Spectrometer (TES), CO profiles from Measurement of Pollution in the Troposphere (MOPITT), and O3 and HNO3 profiles from Microwave Limb Sounder (MLS) using an ensemble Kalman filter technique. Chemical concentrations of various species and emission sources of several precursors are simultaneously optimized. This is expected to improve the emission inversion because the emission estimates are influenced by biases in the modelled tropospheric chemistry, which can be partly corrected by also optimizing the concentrations. We present detailed distributions of the estimated emission distributions for all major regions, the diurnal and seasonal variability, and the evolution of these emissions over the 10-year period. The estimated regional total emissions show a strong positive trend over India (+29 % decade−1), China (+26 % decade−1), and the Middle East (+20 % decade−1), and a negative trend over the USA (−38 % decade−1), southern Africa (−8.2 % decade−1), and western Europe (−8.8 % decade−1). The negative trends in the USA and western Europe are larger during 2005–2010 relative to 2011–2014, whereas the trend in China becomes negative after 2011. The data assimilation also suggests a large uncertainty in anthropogenic and fire-related emission factors and an important underestimation of soil NOx sources in the emission inventories. Despite the large trends observed for individual regions, the global total emission is almost constant between 2005 (47.9 Tg N yr−1) and 2014 (47.5 Tg N yr−1).
Highlights
Nitrogen oxides (NOx = NO + NO2) play an important role in air quality, tropospheric chemistry, and climate
The optimized surface nitrogen oxides (NOx) emissions from the multiple-species assimilation improved agreements with Tropospheric Emission Spectrometer (TES) O3 ver. 6 special observations during 2011–2014 for most locations (Table S1 in the Supplement). These results indicate that multiple-species measurements provide important information for improving surface NOx source estimations and improve the chemical consistency including the relation between concentrations and the estimated emissions
Global surface nitrogen oxides (NOx) emissions are estimated for the 10-year period between 2005–2014 from the assimilation of multiple satellite data sets: tropospheric NO2 www.atmos-chem-phys.net/17/807/2017/
Summary
Nitrogen oxides (NOx = NO + NO2) play an important role in air quality, tropospheric chemistry, and climate. Tropospheric NOx concentrations are highly variable in both space and time, reflecting its short chemical lifetime in the atmosphere and the heterogeneous distribution of its sources and sinks. Emission sources are important in determining the amount and distribution of NOx. Natural NOx sources include biogenic emissions from bacteria in soils, biomass burning, and lightning. Anthropogenic NOx sources include fossil fuel and biofuel combustion, emissions from vehicle transport, and industrial emissions. Bottom-up inventories from different sources and regions contain large uncertainties, which result from inaccurate emission factors and activity rates for each source category. Examples include traffic rush hours, economic activity, biomass-burning activity, wintertime heating of buildings, and rain-induced emission pulses of NOx
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