Effectiveness of inter-regional collaborative emission reduction for ozone mitigation under local-dominated and transport-affected synoptic patterns.

Abstract. Currently, mitigating severe particle pollution in autumn and winter is the key to further improving the air quality of China. The source contributions and transboundary transport of fine particles (PM2.5) in pollution episodes are closely related to large-scale or synoptic-scale atmospheric circulation. How to effectively reduce emissions to control haze pollution under different synoptic conditions is rarely reported. In this study, we classify the synoptic conditions over central China from 2013 to 2018 by using Lamb–Jenkinson method and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Final (FNL) operational global analysis data. The effectiveness of emission control to reduce PM2.5 pollution during winter haze episodes under potential synoptic controls is simulated by GEOS-Chem model. Among the 10 identified synoptic patterns, four types account for 87 % of the total pollution days. Two typical synoptic modes are characterized by low surface wind speed and stable weather conditions or high relative humidity (A or C type) over central China due to a high-pressure system or a southwest trough and low-pressure system, blocking pollutants dispersion. Sensitivity simulations show that these two heavy pollution processes are mainly contributed by local emission sources with ∼82 % for A type and ∼85 % for C type, respectively. The other two patterns lead to pollution of transport characteristics affected by northerly or southerly winds (NW or SW type), carrying air pollution from northern or southern China to central China. The contribution of pollution transmission from northern and southern China is 36.9 % and 7.6 %, respectively of PM2.5, and local emission sources contribute 41 % and 69 %, respectively. We also estimate the effectiveness of emission reduction in these four typical severe pollution synoptic processes. By only reducing SO2 and NOx emission and not controlling NH3, the enhanced nitrate counteracts the effect of sulfate reduction on PM2.5 mitigation, with a less than 4 % decrease in PM2.5. In addition, to effectively mitigate haze pollution of NW- and SW-type synoptic-controlled episodes, local emission control actions should be in coordination with regional collaborative actions.

<p><strong>Title:</strong> One million feet view of Level-2 Processing Facility managed at European Centre for Medium-Range Weather Forecasts (ECMWF)</p><p><strong>Authors:</strong> Rakesh Prithiviraj, Ioannis Mallas, Cristiano Zanna </p><p><strong>Affiliation of authors:</strong> European Centre for Medium-Range Weather Forecasts (ECMWF)</p><p><strong>Abstract text</strong><br>Launched in August 2018, European Space Agency’s Aeolus satellite mission measures Earth's wind profile from space. The Aeolus ground segment mainly comprises of:<br>• Flight Operations Segment (FOS) to monitor and control Aeolus satellite and the instrument onboard, <br>• Payload Data Ground Segment (PDGS) for the acquisition and systematic generation of Level-1A and Level-1B products and <br>• Level-2 Processing Facility (L2PF) at ECMWF for the generation and dissemination of Level-2B and Level-2C products. </p><p>ECMWF is both a research institute and a 24/7 operational service, producing global numerical weather predictions and other data for our Member and Co-operating States and the broader community. ECMWF relies on its atmospheric model and data assimilation system which is called the Integrated Forecasting System (IFS) to make weather predictions. ECMWF has one of the largest supercomputer facilities and meteorological data archives in the world.</p><p>This talk focusses on the Aeolus L2PF facility at ECMWF providing an overview of the processing infrastructure, relevant dataflows, monitoring system and presents the technical/system perspective of Aeolus L2PF in the context of weather forecast. The L2PF facility receives L1B data from Aeolus PDGS and systematically generates and disseminates L2B products and L2C products. The centre is also responsible for the generation of meteorological auxiliary data which is one of the critical inputs for the L2B generation.  The talk also shows various components at ECMWF that work together to achieve more than 99% L2B completeness. The components include ECMWF Production Data Store (ECPDS), ECMWF's High Performance Computing Facility (HPCF) and L2PF cluster. </p><p>The talk concludes with references to tests carried out at ECMWF that have demonstrated that new wind profile observations from Aeolus satellite significantly improve weather forecasts, particularly in the southern hemisphere and the tropics. Because the positive impact of Aeolus on the weather predictions, Aeolus data is expected to be part of the operational weather forecast system at ECMWF in January 2020.</p>

The US global model lags the performance of two European competitors in predicting weather up to two weeks ahead.

Abstract. Ground-level observations, reanalyzed meteorological fields and a 3-D global chemical and transport model (GEOS-Chem) were applied in this study to investigate ozone (O3) pollution events (OPEs) in North China (36.5–40.5∘ N, 114.5–119.5∘ E) during 2014–2017. Ozone pollution days (OPDs) were defined as days with maximum daily averaged 8 h (MDA8) concentrations over North China larger than 160 µg m−3, and OPEs were defined as periods with 3 or more consecutive OPDs. Observations showed that there were 167 OPDs and 27 OPEs in North China during 2014–2017, in which 123 OPDs and 21 OPEs occurred from May to July. We found that OPEs in North China occurred under a typical weather pattern with high daily maximum temperature (Tmax), low relative humidity (RH), anomalous southerlies and divergence in the lower troposphere, an anomalous high-pressure system at 500 hPa, and an anomalous downward air flow from 500 hPa to the surface. Under such a weather pattern, chemical production of O3 was high between 800 and 900 hPa, which was then transported downward to enhance O3 pollution at the surface. A standardized index I_OPE was defined by applying four key meteorological parameters, including Tmax, RH, meridional winds at 850 hPa (V850) and zonal winds at 500 hPa (U500). I_OPE can capture approximately 80 % of the observed OPDs and OPEs, which has implications for forecasting OPEs in North China.

Sensitivities of ozone to its precursors during heavy ozone pollution events in the Yangtze River Delta using the adjoint method

The available literature on morbidity risk of cardiovascular diseases associated with ambient ozone pollution is still limited. This study examined the potential acute effects of exposure to ambient ozone pollution on hospital admissions of cardiovascular events in China. A two-stage multi-city time-series study approach was used to explore the associations of exposure to ambient ozone with daily hospital admissions (n = 6 444 441) for cardiovascular events in 70 Chinese cities of prefecture-level or above during 2015-17. A 10 μg/m3 increment in 2-day average daily 8 h maximum ozone concentrations was associated with admission risk increases of 0.46% [95% confidence interval (CI): 0.28%, 0.64%] in coronary heart disease, 0.45% (95% CI: 0.13%, 0.77%) in angina pectoris, 0.75% (95% CI: 0.38%, 1.13%) in acute myocardial infarction (AMI), 0.70% (95% CI: 0.41%, 1.00%) in acute coronary syndrome, 0.50% (95% CI: 0.24%, 0.77%) in heart failure, 0.40% (95% CI: 0.23%, 0.58%) in stroke and 0.41% (95% CI: 0.22%, 0.60%) in ischemic stroke, respectively. The excess admission risks for these cardiovascular events associated with high ozone pollution days (with 2-day average 8-h maximum concentrations ≥100 µg/m3 vs. < 70 µg/m3) ranged from 3.38% (95% CI: 1.73%, 5.06%) for stroke to 6.52% (95% CI: 2.92%, 10.24%) for AMI. Ambient ozone was associated with increased hospital admission risk for cardiovascular events. Greater admission risks for cardiovascular events were observed under high ozone pollution days. These results provide evidence for the harmful cardiovascular effects of ambient ozone and call for special attention on the control of high ozone pollution.

Understanding ozone pollution in the Yangtze River Delta of eastern China from the perspective of diurnal cycles

The European Centre for Medium-Range Weather Forecasts (ECMWF), as one of the leading centres in numerical weather prediction, has been an active user of observations for model evaluation for many years. Many examples exist where detailed experimental studies have inspired model improvement. To establish a link between the Atmospheric Radiation Measurement (ARM) research and ECMWF's model development, funding was provided for an “ARM fellow” at ECMWF. Furthermore, ECMWF has been working closely with ARM related projects for many years. ECMWF provides operational analysis data for the ARM stations (permanent and mobile) as background meteorological information and ECMWF has implemented the Rapid Radiative Transport Model long wave and short wave schemes as radiation codes in the operational system. These codes were developed at Atmospheric and Environmental Research Inc. with ARM support and were extensively evaluated using detailed ARM observations. This short report describes the history of the ARM-fellowship at ECMWF and summarizes the achievements over the last 3 years. The emphasis of the ARM funded work over the last 3 years has been on further development and evaluation of a new shallow convection scheme in the context of ECMWF's Numerical Weather Prediction (NWP) system. The shallow convection scheme is based on the DualM approach which combines Eddy Diffusion with a Dual Mass flux concept. One of the mass fluxes describes the dry updraughts, whereas the second updraught saturates at cloud base and penetrates into the cloud. The new scheme was optimized using single column cases from a wide range of climatological regimes. Further evaluation of the 3-dimensional model using Lidar data from space (CALIPSO) clearly indicates that the resulting cloud structures are much more realistic than the ones produced by the control model (Tiedtke mass flux scheme). Additionally, data from the ARM mobile facility in 2006 in Niamey has been used to evaluate the surface energy balance in the ECMWF model. It turns out that substantial errors exist in the radiative and turbulent fluxes in the Sahel. These energy budget errors are believed to be detrimental to the simulated flow over West Africa. This was the first time that such verification was possible. It is obvious that the radiative impact of aerosols needs further investigation.

Based on ozone monitoring and meteorological data from 2000 to 2015 in Hong Kong, the characteristics of ozone pollution and the influence of meteorological factors on the ozone pollution were analyzed. The results show that:① A seasonal variation of the ozone concentration in Hong Kong is notable:autumn > spring > winter > summer. Days of ozone exceeding the standard value are concentrated in summer and autumn and rarely occur in winter and spring. ② The annual mean ozone concentration of the maximum daily 8-h average (MDA8) in Hong Kong increases from 2000 to 2015, with an average growth rate of 0.77 μg·(m3·a)-1. The 90th percentile concentration of the ozone MDA8 also increases, with an average rate of 1.49 μg·(m3·a)-1. ③ Higher temperatures are necessary for ozone pollution in Hong Kong. The higher the temperature is, the more ozone pollution likely occurs. ④ In most cases, the ozone concentration is negatively correlated with the relative humidity. The higher the relative humidity is, the lower are the ozone and 90th percentile concentrations in Hong Kong. ⑤ When ozone pollution occurs in Hong Kong, prevailing winds tend to shift from northerly or easterly to westerly. In addition, with the increase of the wind speed, the average ozone concentration changes little, but the 90th percentile ozone concentration significantly decreases. ⑥ Precipitation and cloud cover are important factors affecting the ozone concentration. Weather conditions without or with little rain for many consecutive days are necessary for the occurrence of ozone pollution events. However, with the increase of the cloud cover, the average ozone and 90th percentile concentrations continue to decrease. ⑦ In the case of a total solar radiation ≤ 20 MJ·m-2 or sunshine duration ≤ 10 h, the ozone concentration is positively correlated with the solar radiation and sunshine duration. However, in the case of intense solar radiation (total solar radiation>20 MJ·m-2 or duration of sunshine>10 h), the ozone concentrations decrease with increasing solar radiation or duration because strong solar radiation often occurs in the background of sunny weather after rain. At the same time, southerly winds from the sea often prevail, making it difficult for ozone pollution to occur in Hong Kong. ⑧ Ozone excess days in Hong Kong are often accompanied by changes of a series of meteorological conditions including less rain on sunny days, stronger radiation, higher boundary layer height, lower relative humidity, smaller wind speeds, and higher temperatures. The end of the pollution process is accompanied by the opposite weather changes.

: Monthly wind stresses are computed from the European Centre for Medium-Range Weather Forecasts (ECMWF) operational 12 hrly global wind analyses. These are compared with wind stresses derived from the Florida State University (FSU) monthly pseudo stresses (observational data) over the tropical Pacific Ocean domain from 1981-1993. The FSU product is used as the standard for comparison because it was derived using the same procedures and data type. During 1982-1985, ECMWF equatorial trade winds are 25-55% weaker than those from FSU and the wind stress curl is more diffuse in the northern tropical gyre. Stronger topographically-induced wind features occur in the ECMWF product around the Hawaiian Islands and Central American coast. During 1990-1993, equatorial trade wind magnitudes agree to within 20%, primarily due to uncorroborated strengthening of the ECMWF trade winds (a result of ECMWF product modifications). The ECMWF wind stress curl in the northern tropical gyre is more concentrated. The topographically-induced wind features in the ECMWF product around the Hawaiian Islands and along the Central American coast are smaller in size and stronger. The strengthening in these regions is not corroborated by the FSU product.

This study was based on the observation of volatile organic compounds (VOCs), conventional gaseous air pollutants, and meteorological parameters observed at the Xinxiang Municipal Party School site from June to August 2021. The ozone (O3) characteristics and sensitivity of O3 pollution days and the control strategy of its precursors were studied using an observation-based model (OBM). It was found that the meteorological conditions were characterized by high temperature, low humidity, and low pressure in O3-pollution days. The concentrations of O3 and its precursors all increased in the O3 pollution days. Oxygenated volatile organic compounds (OVOCs) and alkanes were the highest-concentration components of VOCs on O3 pollution days in Xinxiang, and OVOCs had the highest ozone formation potential (OFP) and hydroxyl (·OH) reactivity. According to the relative incremental reactivity (RIR) analysis, during the O3 pollution days in Xinxiang, O3sensitivity was in the VOCs-limited regime in June and in the transitional regime in July and August. Ozone production was more sensitive to alkenes and OVOCs. The RIR values of the precursors in June changed throughout the day, but O3 sensitivity remained the VOCs-limited regime. In July and August, O3 sensitivity was the VOCs-limited regime in the morning, transitional regime at noon, transitional and NOx-limited regime, respectively in the afternoon. By simulating different precursor-reduction scenarios, the results showed that the reduction of VOCs was always beneficial to the control of O3, whereas the reduction of NOx had little effect on the control of O3 and a risk of increasing O3.

Abstract. Temperature and ozone data from the sub-millimetre radiometer (SMR) installed aboard the Odin satellite have been examined to study the relationship between temperature and ozone concentration in the lower and upper stratosphere in winter time. The retrieved ozone and temperature profiles have been considered between the range of 24–46 km during the Northern Hemisphere (NH) winter of December 2002 to March 2003 and January to March 2005. A comparison between the ozone mixing ratio and temperature fields has been made for the zonal means, wavenumber one variations and 5-day planetary waves. The amplitude values in temperature variations are ~5 K in the wavenumber one and 0.5–1 K in the 5-day wave. In ozone mixing ratio, the amplitudes reach ~0.5 ppmv in the wavenumber one and 0.05–0.1 ppmv in the 5-day wave. Several stratospheric warming events were observed during the NH winters of 2002/2003 and early 2005. Along with these warming events, amplification of the amplitude has been detected in wavenumber one (up to 30 K in temperature and 1.25 ppmv in ozone) and partly in the 5-day perturbation (up to 2 K in temperature and 0.2 ppmv in ozone). In general, the results show the expected in-phase behavior between the temperature and ozone fields in the lower stratosphere due to dynamic effects, and an out-of-phase pattern in the upper stratosphere, which is expected as a result of photochemical effects. However, these relationships are not valid for zonal means and wavenumber one components when the wave amplitudes are changing dramatically during the strongest stratospheric warming event (at the end of December 2002/beginning of January 2003). Also, for several shorter intervals, the 5-day perturbations in ozone and temperature are not well-correlated at lower heights, particularly when conditions change rapidly. Odin's basic observation schedule provides stratosphere mode data every third day and to validate the reliability of the 5-day waves extracted from the Odin measurements, additional independent data have been analysed in this study: temperature assimilation data by the European Centre for Medium-range Weather Forecasts (ECMWF) for the NH winter of 2002/2003, and satellite measurements of temperature and ozone by the Microwave Limb Sounder (MLS) on board the Aura satellite for the NH winter in early 2005. Good agreement between the temperature fields from Odin and ECMWF data is found at middle latitude where, in general, the 5-day perturbations from the two data sets coincide in both phase and amplitude throughout the examined interval. Analysis of the wavenumber one and the 5-day wave perturbations in temperature and ozone fields from Odin and from Aura demonstrates that, for the largest part of the examined period, quite similar characteristics are found in the spatial and temporal domain, with slightly larger amplitude values seen by Aura. Hence, the comparison between the Odin data, sampled each third day, and daily data from Aura and the ECMWF shows that the Odin data are sufficiently reliable to estimate the properties of the 5-day oscillations, at least for the locations and time intervals with strong wave activity.

Monthly mean, 2.5 deg - x 2.5 deg-resolution, 10-m height wind speeds from the Special Sensor Microwave Imager (SSMI) instrument and the European Center for Medium-Range Weather Forecasts (ECMWF) forecast-analysis system are compared between 60 deg S and 60 deg N during 1988-1991. The SSMI data were uniformly processed while numerous changes were made to the ECMWF forecast-analysis system. The SSMI measurements, which were compared with moored-buoy wind observations, were considered to be a reference data set to evaluate the influence of the changes made to the ECMWF system upon the ECMWF surface wind speed over the ocean. A demonstrable yearly decrease of the difference between SSMI and ECMWF wind speeds occurred in the 10 deg S - 10 deg N region, including the 5 deg S - 5 deg N zone of the Pacific Ocean, where nearly all of the variations occurred in the 160 deg E - 160 deg W region. The apparent improvement of the ECMWF wind speed occurred at the same time as the yearly decrease of the equatorial Pacific SSMI wind speed, which was associated with the natural transition from La Nina to El Nino conditions. In the 10 deg S - 10 deg N tropical Atlantic, the ECMWF wind speed had a 4-year trend, which was not expected nor was it duplicated with the SSMI data. No yearly trend was found in the difference between SSMI and ECMWF surface wind speeds in middle latitudes of the northern and southern hemispheres. The magnitude of the differences between SSMI and ECMWF was 0.4 m s^(-1) or 100 percent larger in the northern than in the southern hemisphere extratropics. In two areas (Arabian Sea and North Atlantic Ocean) where ECMWF and SSMI wind speeds were compared to ship measurements, the ship data had much better agreement with the ECMWF analyses compared to SSMI data. In the 10 deg S - 10 deg N area the difference between monthly standard deviations of the daily wind speeds dropped significantly from 1988 to 1989, but remained constant at about 30 percent for the remaining years. y.

This paper evaluates the extratropical cyclones within three operational global ensembles [the 20-member Canadian Meteorological Centre (CMC), 20-member National Centers for Environmental Prediction (NCEP), and 50-member European Centre for Medium-Range Weather Forecasts (ECMWF)]. The day-0–6 forecasts were evaluated over the eastern United States and western Atlantic for the 2007–15 cool seasons (October–March) using the ECMWF’s ERA-Interim dataset as the verifying analysis. The Hodges cyclone-tracking scheme was used to track cyclones using 6-h mean sea level pressure (MSLP) data. For lead times less than 72 h, the NCEP and ECMWF ensembles have comparable mean absolute errors in cyclone intensity and track, while the CMC errors are larger. For days 4–6 ECMWF has 12–18 and 24–30 h more accuracy for cyclone intensity than NCEP and CMC, respectively. All ensembles underpredict relatively deep cyclones in the medium range, with one area near the Gulf Stream. CMC, NCEP, and ECMWF all have a slow along-track bias that is significant from 24 to 90 h, and they have a left-of-track bias from 120 to 144 h. ECMWF has greater probabilistic skill for intensity and track than CMC and NCEP, while the 90-member multimodel ensemble (NCEP + CMC + ECMWF) has more probabilistic skill than any single ensemble. During the medium range, the ECMWF + NCEP + CMC multimodel ensemble has the fewest cases (1.9%, 1.8%, and 1.0%) outside the envelope compared to ECMWF (5.6%, 5.2%, and 4.1%) and NCEP (13.7%, 10.6%, and 11.0%) for cyclone intensity and along- and cross-track positions.

During the eruption of COVID-19, a citywide lockdown was executed from 26 January to 23 March 2020, in Shenyang, in which the ozone pollution has recorded significant variations. This paper mainly anatomized the comprehensive characteristics and evolution trends of ozone pollution based on the lockdown period in the first half of 2020. Using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and cluster analysis method to establish backward trajectories and channels, the spatial transport process of ozone in the preset period and the causation of typical ozone pollution events were investigated in depth. The results demonstrated that: The ozone concentration pollution in the first half of 2020 was increased than last year. During the lockdown period, the basic pollutants levels were lower than that in pre-lockdown under different proportions, except O3 maximum 8-h moving average (MDA8) was increased by 69.7%, accompanied by the delay of daily peak value, increased pollution days and longer pollution cycle. The typical pollution events were highly consistent with the evolution path of fine aerosol compelled by extreme weather. The ozone concentration and the atmospheric oxidation capacity can be stably maintained at a low level when NO2 concentration remained at 50–70 μg/m3, no matter how much the AQI was. Meanwhile, ozone concentration in the downwind suburban was as low as the central city and soared in few stations amid post-lockdown, simultaneous the correlation between ozone and other pollutants converted from negative to positive. The trajectory indicated that the pollution sources during the lockdown and pre-lockdown were basically Southern Russia, Inner Mongolia, and the three provinces of Northeast China, the pollution from the Bohai Sea provoked ozone pollutants in Shenyang to rebound briskly amid post-lockdown, the pollution of neighboring countries and areas would have a stronger impact on air quality under the effect of lockdown.