Camilla Geels

TransCom model simulations of hourly atmospheric CO2: Analysis of synoptic-scale variations for the period 2002-2003

The ability to reliably estimate CO2 fluxes from current in situ atmospheric CO2 measurements and future satellite CO2 measurements is dependent on transport model performance at synoptic and shorter timescales. The TransCom continuous experiment was designed to evaluate the performance of forward transport model simulations at hourly, daily, and synoptic timescales, and we focus on the latter two in this paper. Twenty-five transport models or model variants submitted hourly time series of nine predetermined tracers (seven for CO2) at 280 locations. We extracted synoptic-scale variability from daily averaged CO2 time series using a digital filter and analyzed the results by comparing them to atmospheric measurements at 35 locations. The correlations between modeled and observed synoptic CO2 variabilities were almost always largest with zero time lag and statistically significant for most models and most locations. Generally, the model results using diurnally varying land fluxes were closer to the observations compared to those obtained using monthly mean or daily average fluxes, and winter was often better simulated than summer. Model results at higher spatial resolution compared better with observations, mostly because these models were able to sample closer to the measurement site location. The amplitude and correlation of model-data variability is strongly model and season dependent. Overall similarity in modeled synoptic CO2 variability suggests that the first-order transport mechanisms are fairly well parameterized in the models, and no clear distinction was found between the meteorological analyses in capturing the synoptic-scale dynamics.

TransCom model simulations of hourly atmospheric CO2 : experimental overview and diurnal cycle results for 2002

[1] A forward atmospheric transport modeling experiment has been coordinated by the TransCom group to investigate synoptic and diurnal variations in CO2. Model simulations were run for biospheric, fossil, and air-sea exchange of CO2 and for SF6 and radon for 2000-2003. Twenty-five models or model variants participated in the comparison. Hourly concentration time series were submitted for 280 sites along with vertical profiles, fluxes, and meteorological variables at 100 sites. The submitted results have been analyzed for diurnal variations and are compared with observed CO2 in 2002. Mean summer diurnal cycles vary widely in amplitude across models. The choice of sampling location and model level account for part of the spread suggesting that representation errors in these types of models are potentially large. Despite the model spread, most models simulate the relative variation in diurnal amplitude between sites reasonably well. The modeled diurnal amplitude only shows a weak relationship with vertical resolution across models; differences in near-surface transport simulation appear to play a major role. Examples are also presented where there is evidence that the models show useful skill in simulating seasonal and synoptic changes in diurnal amplitude.

Towards a climate-dependent paradigm of ammonia emission and deposition

Existing descriptions of bi-directional ammonia (NH3) land–atmosphere exchange incorporate temperature and moisture controls, and are beginning to be used in regional chemical transport models. However, such models have typically applied simpler emission factors to upscale the main NH3 emission terms. While this approach has successfully simulated the main spatial patterns on local to global scales, it fails to address the environment- and climate-dependence of emissions. To handle these issues, we outline the basis for a new modelling paradigm where both NH3 emissions and deposition are calculated online according to diurnal, seasonal and spatial differences in meteorology. We show how measurements reveal a strong, but complex pattern of climatic dependence, which is increasingly being characterized using ground-based NH3 monitoring and satellite observations, while advances in process-based modelling are illustrated for agricultural and natural sources, including a global application for seabird colonies. A future architecture for NH3 emission–deposition modelling is proposed that integrates the spatio-temporal interactions, and provides the necessary foundation to assess the consequences of climate change. Based on available measurements, a first empirical estimate suggests that 5°C warming would increase emissions by 42 per cent (28–67%). Together with increased anthropogenic activity, global NH3 emissions may increase from 65 (45–85) Tg N in 2008 to reach 132 (89–179) Tg by 2100.

Investigating the sources of synoptic variability in atmospheric CO2 measurements over the Northern Hemisphere continents: a regional model study

Continuous measurements of atmospheric CO2 over the continents are potentially powerful tools for understanding regional carbon budgets, but our limited understanding of the processes driving the high-frequency variability in these measurements makes interpretation difficult. In this paper we examine the synoptic variability (⊼days) of surface CO2 concentrations in four continental records from Europe and North America. Three source functions corresponding to the ocean, land biosphere and anthropogenic sources and sinks for CO2 have been implemented in a regional atmospheric transport model. In previous carbon studies, monthly biospheric fluxes have typically been used, but here high spatiotemporal (daily, 1¼×1¼) resolution biospheric fluxes are obtained from the NCAR Land Surface Model (lsm). A high-pass filter is used to remove atmospheric variability on time scales longer than 2 months, and the resulting simulated concentration fields replicates reasonably well the magnitude and seasonality of the synoptic variability across the four observation sites. The phasing of many of the individual events are also captured, indicating that the physical and biogeochemical dynamics driving the model variability likely resemble those in nature.The observations and model results show pronounced summer maxima in the synoptic CO2 concentration variability at the two stations located in North America, while a slightly different seasonality with high variability throughout fall and winter is observed at the European sites. The mechanisms driving these patterns are studied and discussed based on correlations between the concentration anomalies and the driving atmospheric physical variables and surfaces fluxes in the simulations. During the summer, the synoptic variability over the continents has a significant contribution from variations in regional net primary production, which in turn is modulated by regional, synoptic temperature variability. In winter the synoptic variability is partitioned about equally between biospheric and anthropogenic CO2 and is mainly driven by local vertical mixing and synoptic variations in atmospheric circulation working on the large-scale atmospheric gradient. This study highlights the importance for future modeling work of improved high temporal resolution (at least daily) surface biosphere, oceanic and anthropogenic flux estimates as well as high vertical and horizontal spatiotemporal resolution of the driving meteorology.

Modelling Nitrogen Deposition on a Local Scale—A Review of the Current State of the Art

Abstract. Local ammonia emissions from agricultural activities are often associated with high nitrogen deposition in the close vicinity of the sources. High nitrogen (N) inputs may significantly affect the local ecosystems. Over a longer term, high loads may change the composition of the ecosystems, leading to a general decrease in local biodiversity. In Europe there is currently a significant focus on the impact of atmospheric N load on local ecosystems among environmental managers and policy makers. Model tools designed for application in N deposition assessment and aimed for use in the regulation of anthropogenic nitrogen emissions are, therefore, under development in many European countries. The aim of this paper is to present a review of the current understanding and modelling parameterizations of atmospheric N deposition. A special focus is on the development of operational tools for use in environmental assessment and regulation related to agricultural ammonia emissions. For the often large number of environmental impact assessments needed to be carried out by local environmental managers there is, furthermore, a need for simple and fast model systems. These systems must capture the most important aspects of dispersion and deposition of N in the nearby environment of farms with animal production. The paper includes a discussion on the demands on the models applied in environmental assessment and regulation and how these demands are fulfilled in current state-of-the-art models.

Integrated air-quality monitoring - combined use of measurements and models in monitoring programmes

Environmental context. Optimisation of allocated resources, improved quality, and better understanding of processes – these are the main advantages of applying integrated monitoring (IM). The paper describes IM as a combination of air pollution measuring and modelling, and describes how it is implemented in air-quality management in Denmark. However, the IM concept may also be applied to follow air-quality levels in other countries that currently do not have a corresponding system. It may also be applied to the environmental monitoring of other compartments. Abstract. Integrated air-quality monitoring (IM) is here defined as monitoring based on the combination of results of atmospheric measurements from usually fixed site stations, and results obtained from calculations with air-quality models. This paper outlines experience from the use of IM at the National Environmental Research Institute (NERI) within the two nationwide air-quality monitoring programmes for the Danish urban and rural environments, respectively. The measurements in these Danish monitoring programmes are used to determine actual levels and trends in pollutant concentrations and depositions of pollutants. The measurements are further used for process understanding, and for the development and validation of air-quality models. The results from the air-quality models are used in the interpretation of measurements, but they are also used to provide information about, for example, source apportionment. The model calculations are used to extend the geographical coverage of the monitoring, and to provide information about pollution loads at locations or regions that are not well covered by the limited number of measurement stations in the monitoring programmes. Finally, the air-quality models are applied to carry out scenario studies of future pollution loads, e.g. assessment of the effects of various emission reduction strategies. NERI operates and holds the overall responsibility for the Danish air-quality monitoring programmes. These monitoring programmes are designed to fulfil the Danish obligations in relation to the EU directives on air quality, as well as the Danish obligations in relation to the reporting of data to international organisations (EMEP, HELCOM, OSPARCOM, and WHO). The obtained results from the use of IM form the basis for the national assessment of the air pollution loads in relation to protection of the aquatic and terrestrial environment; in these assessments the use of IM plays a central role.

Future Premature Mortality Due to O3, Secondary Inorganic Aerosols and Primary PM in Europe — Sensitivity to Changes in Climate, Anthropogenic Emissions, Population and Building Stock

Air pollution is an important environmental factor associated with health impacts in Europe and considerable resources are used to reduce exposure to air pollution through emission reductions. These reductions will have non-linear effects on exposure due, e.g., to interactions between climate and atmospheric chemistry. By using an integrated assessment model, we quantify the effect of changes in climate, emissions and population demography on exposure and health impacts in Europe. The sensitivity to the changes is assessed by investigating the differences between the decades 2000–2009, 2050–2059 and 2080–2089. We focus on the number of premature deaths related to atmospheric ozone, Secondary Inorganic Aerosols and primary PM. For the Nordic region we furthermore include a projection on how population exposure might develop due to changes in building stock with increased energy efficiency. Reductions in emissions cause a large significant decrease in mortality, while climate effects on chemistry and emissions only affects premature mortality by a few percent. Changes in population demography lead to a larger relative increase in chronic mortality than the relative increase in population. Finally, the projected changes in building stock and infiltration rates in the Nordic indicate that this factor may be very important for assessments of population exposure in the future.

Modelling of the Atmospheric Transport and Deposition of Ammonia at a National and Regional Scale

Modelling of the Atmospheric Transport and Deposition of Ammonia at a National and Regional Scale

Is the ozone climate penalty robust in Europe

Ozone air pollution is identified as one of the main threats bearing upon human health and ecosystems, with 25 000 deaths in 2005 attributed to surface ozone in Europe (IIASA 2013 TSAP Report #10). In addition, there is a concern that climate change could negate ozone pollution mitigation strategies, making them insufficient over the long run and jeopardising chances to meet the long term objective set by the European Union Directive of 2008 (Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008) (60 ppbv, daily maximum). This effect has been termed the ozone climate penalty. One way of assessing this climate penalty is by driving chemistry-transport models with future climate projections while holding the ozone precursor emissions constant (although the climate penalty may also be influenced by changes in emission of precursors). Here we present an analysis of the robustness of the climate penalty in Europe across time periods and scenarios by analysing the databases underlying 11 articles published on the topic since 2007, i.e. a total of 25 model projections. This substantial body of literature has never been explored to assess the uncertainty and robustness of the climate ozone penalty because of the use of different scenarios, time periods and ozone metrics. Despite the variability of model design and setup in this database of 25 model projection, the present meta-analysis demonstrates the significance and robustness of the impact of climate change on European surface ozone with a latitudinal gradient from a penalty bearing upon large parts of continental Europe and a benefit over the North Atlantic region of the domain. Future climate scenarios present a penalty for summertime (JJA) surface ozone by the end of the century (2071–2100) of at most 5 ppbv. Over European land surfaces, the 95% confidence interval of JJA ozone change is [0.44; 0.64] and [0.99; 1.50] ppbv for the 2041–2070 and 2071–2100 time windows, respectively.

Long-Term Calculations with a Comprehensive Nested Hemispheric Air Pollution Transport Model

The Danish Eulerian Hemispheric Model (DEHM) developed at the National Environmental Research Institute (NERI) in Denmark has been applied for numerous studies of air pollution. DEHM was originally developed with the main purpose of investigating the atmospheric transport of pollutants to the Arctic region, but is now also applied for more local scale environmental problems. The DEHM model has therefore recently been developed with nesting capabilities, which allows for a large mother domain (the Northern Hemisphere) as well as one or two nested domains each with a three times higher horizontal resolution over a limited area. The chemistry version of the model (DEHM-REGINA) has recently been run for a period of 14 years with a nested domain covering Europe and driven by meteorological data from the nested MM5 model. A chemical scheme with 60 species is included and the long-term calculations were made possible due to the application of a new low-cost Linux cluster system recently implemented at NERI. Examples from the validation of the model show that the observed variations and tendencies on both daily to seasonal and longer time scales are well captured for both primary and secondary air pollution components.