Jun-ichi Kurokawa

Key chemical NOx sink uncertainties and how they influence top-down emissions of nitrogen oxides

Triggered by recent developments from laboratory and field studies regarding major NO x sink pathways in the troposphere, this study evaluates the influence of chemical uncertainties in NOx sinks for global NOx distributions calculated by the IMAGESv2 chemistry-transport model, and quantifies their significance for top-down NO x emission estimates. Our study focuses on five key chemical parameters believed to be of primary importance, more specifically, the rate of the reaction of NO2 with OH radicals, the newly identified HNO3-forming channel in the reaction of NO with HO 2, the reactive uptake of N2O5 and HO2 by aerosols, and the regeneration of OH in the oxidation of isoprene. Sensitivity simulations are performed to estimate the impact of each source of uncertainty. The model calculations show that, although the NO2+OH reaction is the largest NO x sink globally accounting for ca. 60 % of the total sink, the reactions contributing the most to the overall uncertainty are the formation of HNO 3 in NO+HO2, leading to NOx column changes exceeding a factor of two over tropical regions, and the uptake of HO 2 by aqueous aerosols, in particular over East and South Asia. Emission inversion experiments are carried out using model settings which either minimise (MINLOSS) or maximise (MAXLOSS) the total NOx sink, both constrained by one year of OMI NO2 column data from the DOMINO v2 KNMI algorithm. The choice of the model setup is found to have a major impact on the top-down flux estimates, with 75 % higher emissions for MAXLOSS compared to the MINLOSS inversion globally. Even larger departures are found for soil NO (factor of 2) and lightning (1.8). The global anthropogenic source is better constrained (factor of 1.57) than the natural sources, except over Sou h Asia where the combined uncertainty primarily associated to the NO+HO 2 reaction in summer and HO2 uptake by aerosol in winter lead to top-down emission differences exceeding a factor of 2. Evaluation of the emission optimisation is performed against independent satellite observations from the SCIAMACHY sensor, with airborne NO2 measurements of the INTEX-A and INTEX-B campaigns, as well as with two new bottom-up inventories of anthropogenic emissions in Asia (REASv2) and China (MEIC). Neither the MINLOSS nor the MAXLOSS setup succeeds in providing the best possible match with all independent datasets. Whereas the minimum sink assumption leads to better agreement with aircraft NO2 profile measurements, consistent with the results of a previous analysis ( Henderson et al. , 2012), the same assumption leads to unrealistic features in the inferred distribution of emissions over China. Clearly, although our study addresses an important issue which was largely overlooked in previous inversion exercises, and demonstrates the strong influence of NOx loss uncertainties on top-down emission fluxes, additional processes need to be considered which could also influence the inferred source. Published by Copernicus Publications on behalf of the European Geosciences Union. 9058 T. Stavrakou et al.: Impact of NOx sink uncertainties on top-down NOx emissions

Emission and atmospheric transport of particulate PAHs in Northeast Asia.

The emission, concentration levels, and transboundary transport of particulate polycyclic aromatic hydrocarbons (PAHs) in Northeast Asia were investigated using particulate PAH measurements, the newly developed emission inventory (Regional Emission inventory in ASia for Persistent Organic Pollutants version, REAS-POP), and the chemical transport model (Regional Air Quality Model ver2 for POPs version, RAQM2-POP). The simulated concentrations of the nine particulate PAHs agreed well with the measured concentrations, and the results firmly established the efficacy of REAS/RAQM2-POP. It was found that the PAH concentrations in Beijing (China, source region), which were emitted predominantly from domestic coal, domestic biofuel, and other transformations of coal (including coke production), were approximately 2 orders of magnitude greater than those monitored at Noto (Japan, leeward region). In Noto, the PAH concentrations showed seasonal variations; the PAH concentrations were high from winter to spring due to contributions from domestic coal, domestic biofuel, and other transformations of coal, and low in summer. In summer, these contribution were decrease, instead, other sources, such as the on-road mobile source, were relatively increased compared with those in winter. These seasonal variations were due to seasonal variations in emissions from China, as well as transboundary transport across the Asian continent associated with meteorological conditions.

Remote sensing evidence of decadal changes in major tropospheric ozone precursors over East Asia

Recent regulatory policies in East Asia reduce ozone precursors, but these changes are spatially and temporally nonuniform. This study investigates variations in the long-term trends of tropospheric NO2, HCHO, and HCHO/NO2 ratios to diagnose ozone sensitivity to changes in NOx and volatile organic compound using the Ozone Monitoring Instrument (OMI). Using an adaptive-degree polynomial filter, we identify extremums of time series of NO2 to determine when and how NO2 change. Due to the regulations in China, trends which were predominantly upward turned downward. The years undergoing these changes primarily happened in 2011 and 2012. OMI column densities, however, suggest that NOx sources in South Korea, the Pearl River Delta (PRD), Taiwan, and Japan have not consistently decreased. Specifically, as Chinese exports of NO2 started subsiding, increasing trends in NO2 columns over several Korean cities, including Seoul, become evident. To quantify the changes in NOx emissions from summertime 2010 to 2014, we conduct a 3D-Var inverse modeling using a regional model with MIX-Asia inventory and estimate NOx emissions (in 2010 and 2014) for the PRD (1.6 and 1.5 Gg/d), the Yangtze River Delta (3.9 and 3.0 Gg/d), north China (15.6 and 14.3 Gg/d), South Korea (1.6 and 1.5 Gg/d), and Japan (2.7 and 2.6 Gg/d). OMI HCHO shows upward trends in East Asia resulting from anthropogenic effects; however, the magnitudes are negative in the PRD, Japan, North Korea, and Taiwan. OMI HCHO/NO2 ratios reveal that while South Korea, Japan, and the south of China have undergone toward more NOx-sensitive regime, areas around the Bohai Sea have become more NOx saturated.

Long-Term Simulations of Surface Ozone in East Asia During 1980 – 2020 with CMAQ and REAS Inventory

Long-term simulations of surface ozone (O3) over East Asia during 1980–2020 were conducted using the regional scale chemical transport model (CMAQ) and the newly developed year-by-year emission inventory in Asia (REAS). The CMAQ with the REAS could reproduce the spatial and seasonal variations of the observed surface O3 concentrations in 2000 and 2001. The historical simulation from 1980 to 2003 demonstrates that an annually-averaged concentration of surface O3 over the Central East China (CEC) and Japan increases about 12 ppbv (1% year−1) and 5 ppbv (0.4% year−1) during a quarter century, respectively. This simulated trend in Japan generally agrees with the observed trend measured at monitoring stations and is correlated with the trend of Chinese NOx and NMVOC emissions. The future emissions up to 2020 were projected based on three emission scenarios (PSC, REF, and PFC). In 2020, the Chinese NOx emissions in each scenario are expected to increase by −1% (PSC), +40% (REF), and +128% (PFC) from 2000, respectively. The worst scenario (PFC) shows that the East Asian NOx emissions almost double between 2000 and 2020. We find that the surface O3 concentrations in East Asia will increase significantly in the near future due to projected increases in NOx emissions.

Source contribution analysis of surface particulate polycyclic aromatic hydrocarbon concentrations in northeastern Asia by source-receptor relationships.

We analyzed the source-receptor relationships for particulate polycyclic aromatic hydrocarbon (PAH) concentrations in northeastern Asia using an aerosol chemical transport model. The model successfully simulated the observed concentrations. In Beijing (China) benzo[a]pyren (BaP) concentrations are due to emissions from its own domain. In Noto, Oki and Tsushima (Japan), transboundary transport from northern China (>40 °N, 40-60%) and central China (30-40 °N, 10-40%) largely influences BaP concentrations from winter to spring, whereas the relative contribution from central China is dominant (90%) in Hedo. In the summer, the contribution from Japanese domestic sources increases (40-80%) at the 4 sites. Contributions from Japan and Russia are additional source of BaP over the northwestern Pacific Ocean in summer. The contribution rates for the concentrations from each domain are different among PAH species depending on their particulate phase oxidation rates. Reaction with O3 on particulate surfaces may be an important component of the PAH oxidation processes.

Verification of NOx emission inventories over North Korea.

In this study, the top-down NOx emissions estimated from satellite observations of NO2 vertical column densities over North Korea from 1996 to 2009 were analyzed. Also, a bottom-up NOx emission inventory from REAS 1.1 from 1980 to 2005 was analyzed with several statistics. REAS 1.1 was in good agreement with the top-down approach for both trend and amount. The characteristics of NOx emissions in North Korea were quite different from other developed countries including South Korea. In North Korea, emissions from industry sector was the highest followed by transportation sector in the 1980s. However, after 1990, the NOx emissions from other sector, mainly agriculture, became the 2nd highest. Also, no emission centers such as urban areas or industrial areas were distinctively observed. Finally, the monthly NOx emissions were high during the warm season.

Algorithm improvement and validation of National Institute for Environmental studies ozone differential absorption lidar at the Tsukuba Network for Detection of Stratospheric Change complementary station

Recently, a data processing and retrieval algorithm (version 2) for ozone, aerosol, and temperature lidar measurements was developed for an ozone lidar system at the National Institute for Environmental Studies (NIES) in Tsukuba (36 degrees N,140 degrees E), Japan. A method for obtaining the aerosol boundary altitude and the aerosol extinction-to-backscatter ratio in the version 2 algorithm enables a more accurate determination of the vertical profiles of aerosols and a more accurate correction of the systematic errors caused by aerosols in the vertical profile of ozone. Improvements in signal processing are incorporated for the correction of systematic errors such as the signal-induced noise and the dead-time effect. The mean vertical ozone profiles of the NIES ozone lidar were compared with those of the Stratospheric Aerosol and Gas Experiment II (SAGE II); they agreed well within a 5% relative difference in the 20-40 km altitude range and within 10% up to 45 km. The long-term variations in the NIES ozone lidar also showed good coincidence with the ozonesonde and SAGE II at 20, 25, 30, and 35 km. The temperatures retrieved from the NIES ozone lidar and those given by the National Center for Environmental Prediction agreed within 7 K in the 35-50 km range.

Impacts of Biomass Burning Emissions on Tropospheric NO 2 Vertical Column Density over Continental Southeast Asia

The behavior of tropospheric NO2 vertical column density (VCD) over continental Southeast Asia (Cambodia, Laos, Myanmar, Thailand, and Vietnam) was systematically analyzed using observations from the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) and a regional chemical transport model (CTM) during 2003–2008. NO2 VCD over continental Southeast Asia showed a distinctive large peak from winter (December) to early spring (April). The regional CTM was configured with anthropogenic emissions taken from the Regional Emission inventory in Asia (REAS) version 2.1 and biomass burning emissions taken from the Global Fire Emissions Database (GFED) version 3.1. Overall, the model could reproduce the NO2 VCD observed by space-borne sensors. A mismatch between satellite observations and the regional CTM was found only in January over Cambodia. A likely reason for this mismatch was diurnal variation in biomass burning emissions. During the analysis period, the largest biomass burning event was reported from December 2003 to April 2004, and a sensitivity analysis was conducted by omitting the biomass burning emissions in the CTM. It was found that the seasonal variations of NO2 VCD, with the peak during winter to early spring, were caused by biomass burning emissions in all countries in continental Southeast Asia. The contribution of biomass burning emissions to NO2 VCD over continental Southeast Asia was an average of 28% during this period and a maximum of 58% in March 2004.

Source–Receptor Relationship Analysis of the Atmospheric Deposition of PAHs Subject to Long-Range Transport in Northeast Asia

The source-receptor relationship analysis of PAH deposition in Northeast Asia was investigated using an Eulerian regional-scale aerosol chemical transport model. Dry deposition (DD) of PAH was controlled by wind flow patterns, whereas wet deposition (WD) depended on precipitation in addition to wind flow patterns. The contribution of WD was approximately 50-90% of the total deposition, except during winter in Northern China (NCHN) and Eastern Russia (ERUS) because of the low amount of precipitation. The amount of PAH deposition showed clear seasonal variation and was high in winter and low in summer in downwind (South Korea, Japan) and oceanic-receptor regions. In the downwind region, the contributions from NCHN (WD 28-52%; DD 54-55%) and Central China (CCHN) (WD 43-65%; DD 33-38%) were large in winter, whereas self-contributions (WD 20-51%; DD 79-81%) were relatively high in summer. In the oceanic-receptor region, the deposition amount decreased with distance from the Asian continent. The amount of DD was strongly influenced by emissions from neighboring domains. The contributions of WD from NCHN (16-20%) and CCHN (28-35%) were large. The large contributions from China in summer to the downwind region were linked to vertical transport of PAHs over the Asian continent associated with convection.