Permafrost thaw driven changes in hydrology and vegetation cover increase trace gas emissions and climate forcing in Stordalen Mire from 1970 to 2014

Permafrost thaw increases active layer thickness, changes landscape hydrology and influences vegetation species composition. These changes alter belowground microbial and geochemical processes, affecting production, consumption and net emission rates of climate forcing trace gases. Net carbon dioxide (CO 2 ) and methane (CH 4 ) fluxes determine the radiative forcing contribution from these climate-sensitive ecosystems. Permafrost peatlands may be a mosaic of dry frozen hummocks, semi-thawed or perched sphagnum dominated areas, wet permafrost-free sedge dominated sites and open water ponds. We revisited estimates of climate forcing made for 1970 and 2000 for Stordalen Mire in northern Sweden and found the trend of increasing forcing continued into 2014. The Mire continued to transition from dry permafrost to sedge and open water areas, increasing by 100% and 35%, respectively, over the 45-year period, causing the net radiative forcing of Stordalen Mire to shift from negative to positive. This trend is driven by transitioning vegetation community composition, improved estimates of annual CO 2 and CH 4 exchange and a 22% increase in the IPCC's 100-year global warming potential (GWP_100) value for CH 4 . These results indicate that discontinuous permafrost ecosystems, while still remaining a net overall sink of C, can become a positive feedback to climate change on decadal timescales. This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 2)’.

Air Quality over China

The strong economic growth in China in recent decades, together with meteorological factors, has resulted in serious air pollution problems, in particular over large industrialized areas with high population density. To reduce the concentrations of pollutants, air pollution control policies have been successfully implemented, resulting in the gradual decrease of air pollution in China during the last decade, as evidenced from both satellite and ground-based measurements. The aims of the Dragon 4 project “Air quality over China” were the determination of trends in the concentrations of aerosols and trace gases, quantification of emissions using a top-down approach and gain a better understanding of the sources, transport and underlying processes contributing to air pollution. This was achieved through (a) satellite observations of trace gases and aerosols to study the temporal and spatial variability of air pollutants; (b) derivation of trace gas emissions from satellite observations to study sources of air pollution and improve air quality modeling; and (c) study effects of haze on air quality. In these studies, the satellite observations are complemented with ground-based observations and modeling.

Error assessment of traffic emission estimates using novel mobility datasets.

<p><span>The COVID-19 pandemic led to widespread reductions in mobility and induced observable changes in the atmosphere. Recent work has employed novel mobility datasets as a proxy for trace gas emissions from traffic, yet there has been little work evaluating these emission numbers. </span></p><p><span>We systematically compare mobility datasets from TomTom and Apple to traffic data from local governments in seven diverse urban and rural regions to characterize the magnitude of errors in emissions that result from using those mobility datasets as a proxy for traffic. We observe differences in excess of 60% between these mobility datasets and local traffic data, which result in large errors in emission estimates. These differences are in part driven by the usage of different baselines and the neglect of seasonality, but mainly they are caused by the individual representations of the datasets. The relationship varies strongly depending on time and region and therefore no general functional relationship between mobility data and traffic flow over all regions can be determined. Future work should be cautious when using these mobility metrics for emission estimates. Further, we use the local government data to identify actual emission reductions from traffic in the range of 7-22% in 2020 compared to 2019 for our study regions. Our full analysis is summarized in Gensheimer et al. (2020).</span></p><p><span>Gensheimer, J., Turner, A., Shekhar, A., Wenzel, A., & Chen, J. (2020). What are different measures of mobility changes telling us about emissions during the COVID-19 pandemic? Earth and Space Science Open Archive, 11. Retrieved from doi: 10.1002/essoar.10504783.1</span></p>

Evidence of secondary organic aerosols formation by non-methane hydrocarbons condensation in cold Pyro-cumulonimbus (pyroCb) outflows

<p>Particle and trace gas emissions can undergo rapid changes in the atmosphere as a result of evaporation, condensation, and coagulation processes that are driven by dynamics and photochemistry.  Here we analyze the fate of non-methane hydrocarbons (NMHCs) gases emitted by intense fires associated with pyroCbs towers that rise and cool rapidly and undergo relatively little dilution as they loft smoke into the upper troposphere and lower stratosphere.  We use airborne observations of plumes from the Williams Flats Fire over the continental United States taken during 2019 FIREX-AQ campaign.  Trace gas data from both fresh boundary smoke and PyroCb-lofted smoke from this fire are compared to that from smoke plumes that stayed at lower altitudes to constrain the roles of condensation, cloud processing and photochemistry in the outflow of pyroCbs.  In the pyroCb outflows we observe lower CO normalized NMHCs mixing ratios with low vapor pressure compared to the boundary layer samples while for high vapor pressure compounds there is little difference between the CO normalized NMHC mixing ratios observed in the different fresh smoke plumes.  Associated with this decrease in condensable NMHCs we find an increase in particle concentrations, specifically at large sizes (~350nm). These multiple observational facts are used to estimate the secondary organic aerosol production by NMHC condensation in pyroCb.  Further analysis of FIREX-AQ data will be used to elucidate the roles of solubility and photochemistry on SOA formation in pyroCbs. These FIREX-AQ results will be used to inform cloud resolving large eddy simulation (LES, HIGRAD) to examine deep convective fire impacts on long range smoke impacts on climate and air quality.</p>

Global NWP Modeling of urban environments at ~1km resolution

<p>Urban areas make up only a small fraction of the Earth’s surface; however, they are home to over 50% of the global population. Accurate numerical weather prediction (NWP) forecasts in these areas offer clear societal benefits; however, land-atmosphere interactions are significantly different between urban and non-urban environments. Forecasting urban weather requires higher model resolution than the size of the urban domain, which is often achievable by regional but not global NWP models. Here we present the preliminary implementation of an urban scheme within the land surface component of the global Integrated Forecasting System (IFS), at recently developed ~1km horizontal resolution. We evaluate the representation error of fluxes and NWP variables at coarser resolutions (~9 km and ~31 km), using the high resolution as truth. We evaluate the feasibility of the scheme and its urban representation at ~1km scales. Availability of urban mapping data limit the affordable complexity of the global scheme; however, using generalisations model performance is improved over urban sites, even adopting simple schemes, and the modelled Urban Heat Island effects show broad agreement with observations. Several directions for future work are explored including a more complex urban representation, restructuring of the urban tiling and the introduction of an urban emissions model for trace gas emissions.<strong> </strong></p>

Precise multispecies agricultural gas flux determined using broadband open-path dual-comb spectroscopy

Advances in spectroscopy have the potential to improve our understanding of agricultural processes and associated trace gas emissions. We implement field-deployed, open-path dual-comb spectroscopy (DCS) for precise multispecies emissions estimation from livestock. With broad atmospheric dual-comb spectra, we interrogate upwind and downwind paths from pens containing approximately 300 head of cattle, providing time-resolved concentration enhancements and fluxes of CH4, NH3, CO2, and H2O. The methane fluxes determined from DCS data and fluxes obtained with a colocated closed-path cavity ring-down spectroscopy gas analyzer agree to within 6%. The NH3 concentration retrievals have sensitivity of 10 parts per billion and yield corresponding NH3 fluxes with a statistical precision of 8% and low systematic uncertainty. Open-path DCS offers accurate multispecies agricultural gas flux quantification without external calibration and is easily extended to larger agricultural systems where point-sampling-based approaches are insufficient, presenting opportunities for field-scale biogeochemical studies and ecological monitoring.

Satellite Monitoring of Anomalous Wildfires in Australia

Here we present the results of satellite monitoring of wildfires in Australia for the period of 2001–2020. Annual and monthly dynamics of wildfire areas and CO and CO2 carbon-bearing trace gas emissions from wildfires have been analyzed for the whole territory of Australia based on satellite data. It was found that anomalous fires occurred in the territory of New South Wales during the 2019–2020 fire season. Values of burned-out areas exceeded the values of previous years 3.5–25.8-fold. Annual mean volumes of carbon-bearing gas emissions in this region exceeded the values of previous years 4–59-fold for carbon monoxide CO and 4.6–50-fold for carbon dioxide CO2. The spatial distribution of the excess concentrations of CO from wildfires in New South Wales was recorded according to the monthly mean data of the AIRS instrument (Aqua satellite). At the same time, the excess of CO2 concentration in the atmosphere was estimated using the TANSO-FTS (GOSAT satellite) data. It was demonstrated that an anomalously high number of fires in this state of Australia was caused by extreme drought associated with abnormally high surface temperatures, low rainfall and humidity which created conditions for intense fires and emissions of carbon-bearing gases associated with the combustion of eucalyptus and tropical rain forests prevailing in this region.