Items

Advanced search

NOx emission estimates during the 2014 Youth Olympic Games in Nanjing

The Nanjing Government applied temporary environmental regulations to guarantee good air quality during the Youth Olympic Games (YOG) in 2014. We study the effect of those regulations by applying the emission estimate algorithm DECSO (Daily Emission estimates Constrained by Satellite Observations) to measurements of the Ozone Monitoring Instrument (OMI). We improved DECSO by updating the chemical transport model CHIMERE from v2006 to v2013 and by adding an Observation minus Forecast (OmF) criterion to filter outlying satellite retrievals due to high aerosol concentrations. The comparison of model results with both ground and satellite observations indicates that CHIMERE v2013 is better performing than CHIMERE v2006. After filtering the satellite observations with high aerosol loads that were leading to large OmF values, unrealistic jumps in the emission estimates are removed. Despite the cloudy conditions during the YOG we could still see a decrease of tropospheric NO2 column concentrations of about 32 % in the OMI observations when compared to the average NO2 columns from 2005 to 2012. The results of the improved DECSO algorithm for NOx emissions show a reduction of at least 25 % during the YOG period and afterwards. This indicates that air quality regulations taken by the local government have an effect in reducing NOx emissions. The algorithm is also able to detect an emission reduction of 10 % during the Chinese Spring Festival. This study demonstrates the capacity of the DECSO algorithm to capture the change of NOx emissions on a monthly scale. We also show that the observed NO2 columns and the derived emissions show different patterns that provide complimentary information. For example, the Nanjing smog episode in December 2013 led to a strong increase in NO2 concentrations without an increase in NOx emissions. Furthermore, DECSO gives us important information on the non-trivial seasonal relation between NOx emissions and NO2 concentrations on a local scale.
Observations of atmospheric mercury in China: a critical review

China presently contributes the largest amount of anthropogenic mercury (Hg) emission into the atmosphere in the world. Over the past decade, numerous studies have been conducted to characterize the concentration and forms of atmospheric Hg in China, which provide insights into the spatial and temporal distributions of atmospheric Hg through ground-based measurements at widely diverse geographical locations and during cruise and flight campaigns. In this paper, we present a comprehensive review of the state of understanding in atmospheric Hg in China. Gaseous elemental mercury (GEM) and particulate-bound mercury (PBM) measured at the remote sites in China are substantially elevated compared to the background values in the Northern Hemisphere. In Chinese urban areas, the highly elevated GEM, PBM and gaseous oxidized mercury (GOM) were mainly derived from local anthropogenic Hg emissions, whereas regional anthropogenic emissions and long-range transport from domestic source regions are the primary causes of the elevated GEM and PBM concentrations at remote sites. Using 7–9 years of continuous observations at a remote site and an urban site, a slight increase in atmospheric GEM (2.4–2.5 % yr−1) was identified (paired samples test: p < 0.01), which is in agreement with the increasing domestic anthropogenic emissions. Anthropogenic GEM emission quantity in China estimated through the observed GEM / CO concentration ratios ranged from 632 to 1138 t annually over the past decade, 2–3 times larger than published values using emission activity data. Modeling results and filed measurements show dry deposition is the predominant process for removing Hg from the atmosphere, 2.5–9.0 times larger than wet deposition, due to the elevated atmospheric GEM and PBM concentrations that facilitate dry deposition to terrestrial landscapes. Further studies to reconcile the observed and simulated Hg concentrations, to understand the impact of domestic emission reduction on Hg concentration and deposition and to delineate the role of Hg emission and deposition of China in the global Hg biogeochemical cycle, are needed.
Observation of a tidal effect on the Polar Jet Stream

Variations in the Polar Jet Stream directly affect weather across Europe and North America (Francis et al., 2012). Jet Stream dynamics are governed by the development of planetary Rossby waves (Dickinson, 1978) driven by variation of the Coriolis force with latitude. Here we show that increasing atmospheric tides induce the development of Rossby waves, especially during winter months. This changes the flow and direction of the Jet Stream, as measured by the Arctic Oscillation (AO). Although horizontal tidal forces are tiny (107 smaller than gravity), they act over huge areas dragging the Jet Stream flow southwards in regular pulses as the earth rotates. This induces a changing Coriolis torque, which then distorts the Jet Stream flow. The data from eight recent winters are studied indicating that the AO is anti-correlated to the horizontal "tractional" component of tides acting between latitude 45 and 60° N. The observed 28 day cycle in Jet Stream flow and extent has a statistical significance > 99 %. A cross-correlation between all daily AO data since 1950 and the tractional tidal strength shows a significant anti-correlation with a lag time of ~ 5 days. The strongest correlation and largest excursions of the AO are observed during winter 2005/2006 – a maximum lunar standstill year. This declination dependence of tidal forces at high latitudes is the proposed cause of many previous reports of an 18.6 year dependence of continental rainfall and drought.
Modelled and observed changes in aerosols and surface solar radiation over Europe between 1960 and 2009

Substantial changes in anthropogenic aerosols and precursor gas emissions have occurred over recent decades due to the implementation of air pollution control legislation and economic growth. The response of atmospheric aerosols to these changes and the impact on climate are poorly constrained, particularly in studies using detailed aerosol chemistry–climate models. Here we compare the HadGEM3-UKCA (Hadley Centre Global Environment Model-United Kingdom Chemistry and Aerosols) coupled chemistry–climate model for the period 1960–2009 against extensive ground-based observations of sulfate aerosol mass (1978–2009), total suspended particle matter (SPM, 1978–1998), PM10 (1997–2009), aerosol optical depth (AOD, 2000–2009), aerosol size distributions (2008–2009) and surface solar radiation (SSR, 1960–2009) over Europe. The model underestimates observed sulfate aerosol mass (normalised mean bias factor (NMBF) = −0.4), SPM (NMBF = −0.9), PM10 (NMBF = −0.2), aerosol number concentrations (N30 NMBF = −0.85; N50 NMBF = −0.65; and N100 NMBF = −0.96) and AOD (NMBF = −0.01) but slightly overpredicts SSR (NMBF = 0.02). Trends in aerosol over the observational period are well simulated by the model, with observed (simulated) changes in sulfate of −68 % (−78 %), SPM of −42 % (−20 %), PM10 of −9 % (−8 %) and AOD of −11 % (−14 %). Discrepancies in the magnitude of simulated aerosol mass do not affect the ability of the model to reproduce the observed SSR trends. The positive change in observed European SSR (5 %) during 1990–2009 ("brightening") is better reproduced by the model when aerosol radiative effects (ARE) are included (3 %), compared to simulations where ARE are excluded (0.2 %). The simulated top-of-the-atmosphere aerosol radiative forcing over Europe under all-sky conditions increased by > 3.0 W m−2 during the period 1970–2009 in response to changes in anthropogenic emissions and aerosol concentrations.
Investigation of error sources in regional inverse estimates of greenhouse gas emissions in Canada

Inversion models can use atmospheric concentration measurements to estimate surface fluxes. This study is an evaluation of the errors in a regional flux inversion model for different provinces of Canada, Alberta (AB), Saskatchewan (SK) and Ontario (ON). Using CarbonTracker model results as the target, the synthetic data experiment analyses examined the impacts of the errors from the Bayesian optimisation method, prior flux distribution and the atmospheric transport model, as well as their interactions. The scaling factors for different sub-regions were estimated by the Markov chain Monte Carlo (MCMC) simulation and cost function minimization (CFM) methods. The CFM method results are sensitive to the relative size of the assumed model-observation mismatch and prior flux error variances. Experiment results show that the estimation error increases with the number of sub-regions using the CFM method. For the region definitions that lead to realistic flux estimates, the numbers of sub-regions for the western region of AB/SK combined and the eastern region of ON are 11 and 4 respectively. The corresponding annual flux estimation errors for the western and eastern regions using the MCMC (CFM) method are -7 and -3 % (0 and 8 %) respectively, when there is only prior flux error. The estimation errors increase to 36 and 94 % (40 and 232 %) resulting from transport model error alone. When prior and transport model errors co-exist in the inversions, the estimation errors become 5 and 85 % (29 and 201 %). This result indicates that estimation errors are dominated by the transport model error and can in fact cancel each other and propagate to the flux estimates non-linearly. In addition, it is possible for the posterior flux estimates having larger differences than the prior compared to the target fluxes, and the posterior uncertainty estimates could be unrealistically small that do not cover the target. The systematic evaluation of the different components of the inversion model can help in the understanding of the posterior estimates and percentage errors. Stable and realistic sub-regional and monthly flux estimates for western region of AB/SK can be obtained, but not for the eastern region of ON. This indicates that it is likely a real observation-based inversion for the annual provincial emissions will work for the western region whereas; improvements are needed with the current inversion setup before real inversion is performed for the eastern region.
Quantifying the contribution of long-range transport to particulate matter (PM) mass loadings at a suburban site in the north-western Indo-Gangetic Plain (NW-IGP)

Many sites in the densely populated Indo-Gangetic Plain (IGP) frequently exceed the national ambient air quality standard (NAAQS) of 100 μg m−3 for 24 h average PM10 and 60 μg m−3 for 24 h average PM2.5 mass loadings, exposing residents to hazardous levels of particulate matter (PM) throughout the year. We quantify the contribution of long-range transport to elevated PM levels and the number of exceedance events through a back-trajectory climatology analysis of air masses arriving at the IISER Mohali Atmospheric Chemistry facility (30.667° N, 76.729° E; 310 m a.m.s.l.) for the period August 2011–June 2013. Air masses arriving at the receptor site were classified into six clusters, which represent synoptic-scale air-mass transport patterns. Long-range transport from the west leads to significant enhancements in the average fine- and coarse-mode PM mass loadings during all seasons. The contribution of long-range transport from the west and south-west (source regions: Arabia, Thar Desert, Middle East and Afghanistan) to coarse-mode PM varied between 9 and 57 % of the total PM10–2.5 mass. Local pollution episodes (wind speed < 1 m s−1) contributed to enhanced PM2.5 mass loadings during both the winter and summer seasons and to enhanced coarse-mode PM only during the winter season. South-easterly air masses (source region: eastern IGP) were associated with significantly lower fine- and coarse-mode PM mass loadings during all seasons. The fraction of days in each season during which the PM mass loadings exceeded the national ambient air quality standard was controlled by long-range transport to a much lesser degree. For the local cluster, which represents regional air masses (source region: NW-IGP), the fraction of days during which the national ambient air quality standard (NAAQS) of 60 μg m−3 for 24 h average PM2.5 was exceeded varied between 36 % of the days associated with this synoptic-scale transport during the monsoon, and 95 % during post-monsoon and winter seasons; the fraction of days during which the NAAQS of 100 μg m−3 for the 24 h average PM10 was exceeded, varied between 48 % during the monsoon and 98 % during the post-monsoon season. Long-range transport was responsible for both, bringing air masses with a significantly lower fraction of exceedance days from the eastern IGP and air masses with a moderate increase in the fraction of exceedance days from the west (source regions: Arabia, Thar Desert, Middle East and Afghanistan). In order to bring PM mass loadings into compliance with the NAAQS and to reduce the number of exceedance days, mitigation of regional combustion sources in the NW-IGP needs to be given highest priority.
Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO2, H2O and dimethyl sulfide

Isoprene is the dominant global biogenic volatile organic compound (VOC) emission. Reactions of isoprene with ozone are known to form stabilised Criegee intermediates (SCIs), which have recently been shown to be potentially important oxidants for SO2 and NO2 in the atmosphere; however the significance of this chemistry for SO2 processing (affecting sulfate aerosol) and NO2 processing (affecting NOx levels) depends critically upon the fate of the SCIs with respect to reaction with water and decomposition. Here, we have investigated the removal of SO2 in the presence of isoprene and ozone, as a function of humidity, under atmospheric boundary layer conditions. The SO2 removal displays a clear dependence on relative humidity, confirming a significant reaction for isoprene-derived SCIs with H2O. Under excess SO2 conditions, the total isoprene ozonolysis SCI yield was calculated to be 0.56 (±0.03). The observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + H2O) / k(SCI + SO2), of 3.1 (±0.5) × 10−5 for isoprene-derived SCIs. The relative rate constant for k(SCI decomposition) / k(SCI+SO2) is 3.0 (±3.2) × 1011 cm−3. Uncertainties are ±2σ and represent combined systematic and precision components. These kinetic parameters are based on the simplification that a single SCI species is formed in isoprene ozonolysis, an approximation which describes the results well across the full range of experimental conditions. Our data indicate that isoprene-derived SCIs are unlikely to make a substantial contribution to gas-phase SO2 oxidation in the troposphere. We also present results from an analogous set of experiments, which show a clear dependence of SO2 removal in the isoprene–ozone system as a function of dimethyl sulfide concentration. We propose that this behaviour arises from a rapid reaction between isoprene-derived SCIs and dimethyl sulfide (DMS); the observed SO2 removal kinetics are consistent with a relative rate constant, k(SCI + DMS) / k(SCI + SO2), of 3.5 (±1.8). This result suggests that SCIs may contribute to the oxidation of DMS in the atmosphere and that this process could therefore influence new particle formation in regions impacted by emissions of unsaturated hydrocarbons and DMS.
Spatial, temporal and vertical distribution of ammonia concentrations over Europe – comparing a static and dynamic approach with WRF-Chem

The study focuses on the application of a dynamic ammonia emission into the Weather Research and Forecasting Chemistry model (WRF-Chem) and the influence on the simulated ammonia concentrations and the overall model performance. We have focused on agricultural ammonia sources and have analysed both hourly and daily patterns of ammonia emissions and concentrations at measurement sites located in agricultural areas or influenced by this activity. For selected episodes, we have also investigated the 3-D patterns of the ammonia concentrations in the atmosphere. The application of the dynamic ammonia emission into the WRF-Chem model (the "DYNAMIC" simulation) results in an improvement of the modelled daily ammonia concentrations in comparison to a static approach (the "BASE" simulation), which is currently widely used in chemical transport models. In the case of hourly resolution, we have observed an improvement for the DYNAMIC approach for the winter and autumn seasons, but for the entire year the modelled hourly ammonia peaks are shifted toward the afternoon hours if compared with measurements. This study indicates that the current description of the diurnal cycle of the ammonia concentration from fields is not accurate and more research is needed in order to improve the processes that describe the emission from fertilised fields. The results suggest that the governing processes in relation to the diurnal cycle are the atmospheric mixing and the emission strength. Therefore, an improved description of the diurnal profile of ammonia concentrations within atmospheric models requires a better description of the planetary boundary layer height and a stronger daily pattern of ammonia emission, e.g. through increased evaporation or increased fluxes from the surface.
Continental pollution in the western Mediterranean basin: vertical profiles of aerosol and trace gases measured over the sea during TRAQA 2012 and SAFMED 2013

In this study we present airborne observations of aerosol and trace gases obtained over the sea in the western Mediterranean basin during the TRAQA (TRansport and Air QuAlity) and SAFMED (Secondary Aerosol Formation in the MEDiterranean) campaigns in summer 2012 and 2013. A total of 23 vertical profiles were measured up to 5000 m above sea level over an extended area (40–45° N and 2° W–12° E) including the Gulf of Genoa, southern France, the Gulf of Lion, and the Spanish coast. During TRAQA and SAFMED the study area experienced a wide range of meteorological conditions which favoured pollution export from different sources located around the basin. Also, several events of dust outflows were measured during the campaigns. Observations from the present study show that continental pollution largely affects the western Mediterranean both close to coastal regions and in the open sea as far as ~ 250 km from the coastline. The measured aerosol scattering coefficient varies between ~ 20 and 120 Mm−1, while carbon monoxide (CO) and ozone (O3) mixing ratios are in the range of 60–165 and 30–85 ppbv, respectively. Pollution reaches 3000–4000 m in altitude and presents a very complex and highly stratified structure characterized by fresh and aged layers both in the boundary layer and in the free troposphere. Within pollution plumes the measured particle concentration in the Aitken (0.004–0.1 μm) and accumulation (0.1–1.0 μm) modes is between ~ 30 and 5000–6000 scm−3 (standard cm−3), which is comparable to the aerosol concentration measured in continental areas under pollution conditions. Additionally, our measurements indicate the presence of highly concentrated Aitken layers (10 000–15 000 scm−3) observed both close to the surface and in the free troposphere, possibly linked to the influence of new particle formation (NPF) episodes over the basin.
Climate extremes in multi-model simulations of stratospheric aerosol and marine cloud brightening climate engineering

Simulations from a multi-model ensemble for the RCP4.5 climate change scenario for the 21st century, and for two solar radiation management (SRM) schemes (stratospheric sulfate injection (G3), SULF and marine cloud brightening by sea salt emission SALT) have been analysed in terms of changes in the mean and extremes of surface air temperature and precipitation. The climate engineering and termination periods are investigated. During the climate engineering period, both schemes, as intended, offset temperature increases by about 60 % globally, but are more effective in the low latitudes and exhibit some residual warming in the Arctic (especially in the case of SALT which is only applied in the low latitudes). In both climate engineering scenarios, extreme temperature changes are similar to the mean temperature changes over much of the globe. The exceptions are the mid- and high latitudes in the Northern Hemisphere, where high temperatures (90th percentile of the distribution) of the climate engineering period compared to RCP4.5 control period rise less than the mean, and cold temperatures (10th percentile), much more than the mean. This aspect of the SRM schemes is also reflected in simulated reduction in the frost day frequency of occurrence for both schemes. However, summer day frequency of occurrence increases less in the SALT experiment than the SULF experiment, especially over the tropics. Precipitation extremes in the two SRM scenarios act differently – the SULF experiment more effectively mitigates extreme precipitation increases over land compared to the SALT experiment. A reduction in dry spell occurrence over land is observed in the SALT experiment. The SULF experiment has a slight increase in the length of dry spells. A strong termination effect is found for the two climate engineering schemes, with large temperature increases especially in the Arctic. Globally, SULF is more effective in reducing extreme temperature increases over land than SALT. Extreme precipitation increases over land is also more reduced in SULF than the SALT experiment. However, globally SALT decreases the frequency of dry spell length and reduces the occurrence of hot days compared to SULF.