Virginie Marécal

Formaldehyde in the Tropical Western Pacific: Chemical Sources and Sinks, Convective Transport, and Representation in CAM-Chem and the CCMI Models

Formaldehyde (HCHO) directly affects the atmospheric oxidative capacity through its effects on HOx. In remote marine environments, such as the Tropical Western Pacific (TWP), it is particularly important to understand the processes controlling the abundance of HCHO because model output from these regions is used to correct satellite retrievals of HCHO. Here, we have used observations from the CONTRAST field campaign, conducted during January and February 2014, to evaluate our understanding of the processes controlling the distribution of HCHO in the TWP as well as its representation in chemical transport/climate models. Observed HCHO mixing ratios varied from ~500 pptv near the surface to ~75 pptv in the upper troposphere. Recent convective transport of near surface HCHO and its precursors, acetaldehyde and possibly methyl hydroperoxide, increased upper tropospheric HCHO mixing ratios by ~33% (22 pptv); this air contained roughly 60% less NO than more aged air. Output from the CAM-Chem chemistry transport model (2014 meteorology) as well as nine chemistry climate models from the Chemistry-Climate Model Initiative (free-running meteorology) are found to uniformly underestimate HCHO columns derived from in situ observations by between 4 and 50%. This underestimate of HCHO likely results from a near factor of two underestimate of NO in most models, which strongly suggests errors in NOx emissions inventories and/or in the model chemical mechanisms. Likewise, the lack of oceanic acetaldehyde emissions and potential errors in the model acetaldehyde chemistry lead to additional underestimates in modeled HCHO of up to 75 pptv (~15%) in the lower troposphere.

Comparison of tropospheric NO 2 columns from MAX-DOAS retrievals and regional air quality model simulations

Multi-axis differential optical absorption spectroscopy (MAX-DOAS) tropospheric NO2 column retrievals from four European measurement stations are compared to simulations from five regional air quality models which contribute to the European regional ensemble forecasts and reanalyses of the operational Copernicus Atmosphere Monitoring Service (CAMS). Compared to other observational data usually applied for regional model evaluation, MAX-DOAS data are closer to the regional model data in terms of horizontal and vertical resolution, and multiple measurements are available during daylight, so that, for example, diurnal cycles of trace gases can be investigated. In general, there is good agreement between simulated and retrieved NO2 column values for individual MAX-DOAS measurements with correlations between 35 % and 70 % for individual models and 45 % to 75 % for the ensemble median for tropospheric NO2 vertical column densities (VCDs), indicating that emissions, transport and tropospheric chemistry of NOx are on average well simulated. However, large differences are found for individual pollution plumes observed by MAX-DOAS. Most of the models overestimate seasonal cycles for the majority of MAX-DOAS sites investigated. At the urban stations, weekly cycles are reproduced well, but the decrease towards the weekend is underestimated and diurnal cycles are overall not well represented. In particular, simulated morning rush hour peaks are not confirmed by MAX-DOAS retrievals, and models fail to reproduce observed changes in diurnal cycles for weekdays versus weekends. The results of this study show that future model development needs to concentrate on improving representation of diurnal cycles and associated temporal scalings. Published by Copernicus Publications on behalf of the European Geosciences Union. 2796 A.-M. Blechschmidt et al.: Comparison of NO2 columns from MAX-DOAS and regional air quality models

Modeling the TTL at Continental Scale for a Wet Season: An Evaluation of the BRAMS Mesoscale Model Using TRO‐Pico Campaign, and Measurements From Airborne and Spaceborne Sensors

In order to better understand the water vapor (WV) intrusion into the tropical stratosphere, a mesoscale simulation of the tropical tropopause layer (TTL) using the BRAMS (Brazilian version of RAMS) model is evaluated for a wet season. This simulation with a horizontal grid-point resolution of 20 km × 20 km cannot resolve the stratospheric overshooting convection (SOC). Its ability to reproduce other key parameters playing a role in the stratospheric WV abundance is investigated using the balloon-borne TRO-Pico campaign measurements, the upper-air soundings over Brazil, and the satellite observations by Aura MLS (Microwave Limb Sounder), MHS (Microwave Humidity Sounder) and GOES-12. The BRAMS exhibits a good ability in simulating temperature, cold-point, WV variability around the tropopause. However, the simulation is typically observed to be warmer by ∼2.0°C and wetter by ∼0.4 ppmv at the hygropause, which can be partly affiliated with the grid-boundary nudging of the model by ECMWF operational analyses. The modeled cloud tops show a good correlation (maximum cross-correlation of ∼0.7) with GOES-12. Furthermore, the overshooting cells detected by MHS are observed at the locations, where 75% of the modeled cloud tops are higher than 11 km. Finally, the modeled inertia-gravity wave periodicity and wavelength are comparable with those deduced from the radio sounding measurements during TRO-Pico campaign. The good behavior of BRAMS confirms the SOC contribution in the WV abundance and variability is of lesser importance than the large-scale processes. This simulation can be used as a reference run for upscaling the impact of SOC at a continental scale for future studies.

A new method (M 3 Fusion-v1) for combining observations and multiple model output for an improved estimate of the global surface ozone distribution

We have developed a new statistical approach (M3Fusion) for combining surface ozone observations from thousands of monitoring sites around the world with the output from multiple atmospheric chemistry models to produce a global surface ozone distribution with greater accuracy than can be provided by any individual model. The ozone observations from 4766 monitoring sites were provided by the Tropospheric Ozone Assessment Report (TOAR) surface ozone database which contains the world’s largest collection of surface ozone metrics. Output from six models was provided by the participants of 5 the Chemistry-Climate Model Initiative (CCMI) and NASA’s Global Modeling and Assimilation Office (GMAO). We analyze the 6-month maximum of the maximum daily 8-hour average ozone value (DMA8) for relevance to ozone health impacts. We interpolate the irregularly-spaced observations onto a fine resolution grid by using integrated nested Laplace approximations, and compare the ozone field to each model in each world region. This method allows us to produce a global surface ozone field based on TOAR observations, which we then use to select the combination of global models with the greatest skill in 10 each of 8 world regions; models with greater skill in a particular region are given higher weight. This blended model product is bias-corrected within two degrees of observation locations to produce the final fused surface ozone product. We show that our fused product has an improved mean squared error compared to the simple multi-model ensemble mean. 1 Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-183 Manuscript under review for journal Geosci. Model Dev. Discussion started: 5 September 2018 c

Impact of Temporal Resolution of Dry Deposition Velocities on Air Quality Modeling

In the framework of global atmospheric composition and air quality forecasting, accurate modeling of atmospheric chemical species redistribution and evolutions in numerical weather and air quality prediction models has become an important challenge in terms of research and developments. Such model developments are a part of the MACCII and MACCIII projects (EU-FP7) done to extend ECMWF’s integrated forecast system (IFS) by adding modules for chemistry, deposition and emission of reactive gases. It is now well known that deposition of chemical species, and especially dry deposition, is a major sink of pollutant in the atmospheric boundary layer. Several parameterizations have been developed in the last decades, while the resistances approach proposed by Wesely (1989) is the most commonly used. However, modeling of dry deposition is confronted to a lack of validation data. Indeed, this kind of parameterization is highly sensible to physical inputs like meteorological and surface fields. Currently, most of models use monthly-means values for dry deposition. It is thus impossible to take into account rapid transitions that can be observed on this inputs and can maybe leads to large biases on the short term forecasts. To investigate impacts of temporal resolution of dry deposition fields on air quality modeling, long simulations were done with the MOCAGE CTM developed at Meteo-France, four type of temporal resolution (monthly-means, daily-means, mean daily-cycle, dynamic velocities) have been used, and results have been evaluated at regional and global scale. They shows important impacts in low-levels atmospheric composition locally, but also at global scale.

European Air Quality Simulations in the Context of IMPACT2C, Focus on Aerosol Concentrations

In the context of the IMPACT2C project, one of the objectives is to estimate the pan-European impacts of a global 2-degree increase in temperature on human health, including change in air pollution. Climate change will affect atmospheric dispersion, biogenic and fire emissions, chemistry, and the frequency of extreme weather situations such as heat waves. These changes will have an impact on air quality with subsequent health consequences that must be evaluated. In order to evaluate how climate change will potentially affect the efficiency of emission abatement policies and how this will potentially affect health, several simulations have been conducted using different chemistry-transport models (CTMs): CHIMERE (IPSL), EMEP MSC-W (MET.NO), MATCH (SMHI), and MOCAGE (Meteo-France). The use of four CTMs provide an estimate of the uncertainty in projections with the spread between models and driving meteorological data. To compare with future climate, the first step is to perform air quality simulations for the current climate: HINDCAST (CTMs forced by reanalysis boundary forcing ERA Interim) and HISTORICAL (global climate model boundary forcings). The comparisons between HINDCAST and HISTORICAL simulations allow to evaluate how global climate models modify climate hindcasts by boundary conditions inputs. In this study, we focus on particulate matter (PM10 and PM2.5) and its chemical composition. We first analyze whether the chemical composition of PM is affected by the use of climate models. We then investigate the contributions of the changes in meteorological parameters (frequency of precipitation, 2-m temperature, etc.) as well as emissions and depositions processes on surface PM. These results are the basis for analyzing future 2° warming climates. Under the RCP4.5 scenario, simulations have been performed in order to calculate the effect of climate change on emission reduction scenarios, the climate penalty, as well as the effect of emission mitigation. This analysis also provide uncertainties associated to future AQ projections.

Impact of Climate on Air Quality in the Mediterranean Basin: Present Climate

Atmospheric pollution is an environmental problem our modern societies have to face with. The Mediterranean basin is a sensible region to atmospheric pollution, especially for air quality issues.