nasa-gesdisc/es-publications-researchareas huggingface dataset:
Spatiotemporal patterns of N2 fixation in coastal waters derived from rate measurements and remote sensing (2020)

Abstract. Coastal lagoons are important sites for nitrogen (N) removal via sediment burial and denitrification. Blooms of heterocystous cyanobacteria may diminish N retention as dinitrogen (N2) fixation offsets atmospheric losses via denitrification. We measured N2 fixation in the Curonian Lagoon, Europe's largest coastal lagoon, to better understand the factors controlling N2 fixation in the context of seasonal changes in phytoplankton community composition and external N inputs. Temporal patterns in N2 fixation were primarily determined by the abundance of heterocystous cyanobacteria, mainly Aphanizomenon flosaquae, which became abundant after the decline in riverine nitrate inputs associated with snowmelt. Heterocystous cyanobacteria dominated the summer phytoplankton community resulting in strong correlations between chlorophyll-a (Chl-a) and N2 fixation. We used regression models relating N2 fixation to Chl-a, along with remote sensing-based estimates of Chl-a to derive lagoon-scale estimates of N2 fixation. N2 fixation by pelagic cyanobacteria was found to be a significant component of the lagoon's N budget based on comparisons to previously derived fluxes associated with riverine inputs, sediment-water exchange and losses via denitrification. To our knowledge, this is the first study to derive ecosystem-scale estimates of N2 fixation by combining remote sensing of Chl-a with empirical models relating N2 fixation rates to Chl-a.

Research areas: Ecosystems
In Situ Observations of Light-Absorbing Carbonaceous Aerosols at Himalaya: Analysis of the South Asian Sources and Trans-Himalayan Valleys Transport Pathways (2020)

The mountain-valleys along the south margin of the Himalaya-Tibetan Plateau (HTP), referred to as trans-Himalayan valleys, are transport pathways of atmospheric pollutants from the South Asia lifting to the HTP based on atmospheric models and satellite detections. However, few field studies can be conducted to confirm the aerosol transport along these valleys due to the harsh environment and limited power supply. Individual particle collection instruments offer the unique advantage of collecting samples and tracing particle sources in remote areas due to their portability and efficiency. In this study, transmission electron microscopy was used to study individual particles collected in two trans-Himalayan valleys. We found that 4970% of thousands of particles were light-absorbing carbonaceous aerosols including soot-bearing and tarball-bearing particles in December of 2017. The dominant sizes of soot-bearing and tarball-bearing particles were 151370 and 198255 nm, respectively. The WRF-Chem model and wind field analyses show that the intense regional air pollution with high mass concentrations of light-absorbing carbonaceous aerosol occurred in the South Asia and southwest wind normally prevailed along the trans-Himalayan valleys in the afternoon of each day during wintertime. Backward trajectory and CALIPSO data further confirm that these light-absorbing carbonaceous aerosols from the South Asia were transported to the southern HTP. These carbonaceous aerosols exhibited significantly internally mixing with secondary sulfates. Here individual particle analysis coupled with the WRF-Chem model, the meteorological observation data, and satellite data confirm the trans-Himalayan valleys as the direct channels for abundant carbonaceous aerosols lifting from the South Asia to the HTP.

Research areas: Air Quality
Analysis of the ETNA 2015 Eruption Using WRFChem Model and Satellite Observations (2020)

The aim of the present work is to utilize a new functionality within the Weather Research and Forecasting model coupled with Chemistry (WRFChem) that allows simulating emission, transport, and settling of pollutants released during the Etna 2015 volcanic activities. This study constitutes the first systematic application of the WRFChem online-based approach to a specific Etna volcanic eruption, with possible effects involving the whole Mediterranean area. In this context, the attention has been focused on the eruption event, recorded from 37 December 2015, which led to the closure of the nearby Catania International Airport. Quantitative meteorological forecasts, analyses of Etna volcanic ash transport, and estimates of the ash ground deposition have been performed. In order to test the performance of the proposed approach, the model outputs have been compared with data provided by satellite sensors and Doppler radars. As a result, it emerges that, as far as the selected eruption event is concerned, the WRFChem model reasonably reproduces the distribution of SO2 and of volcanic ash. In addition, this modeling system may provide valuable support both to airport management and to local stakeholders including public administrations.

Research areas: Volcanic Eruptions
Black carbon pollution simulations: a RegCM4 model projection and assessment during the boreal winter and summer over West Africa region (2020)

The increasing sources of black carbon (BC) emission into the atmosphere have made BC a major air pollutant that could contribute significantly and alter the global atmospheric radiation budget. A perturbed global radiation budget will have profound effect on rainfall cycle and dependent socioeconomic activities. In this paper, RegCM version 4.7, a regional climate model, has been used to simulate back carbon (BC) pollution over West Africa. Pollution-radiation feedback option in the model was activated to determine the effect of radiative properties of BC on climate parameters (rainfall, temperature and wind speed). The study attempted to capture the effect of radiative properties of BC on those climate parameters by activating and de-activating radiation feedback option (RFB) of the model under two RCP2.6 and 8.5. When RFB was turned off, both scenarios showed a decrease in the mean monthly rainfall of up to 2 mm/month in the north and 1.2 mm/month in the south of the West African region. Temperature increased by a factor of 2 K/month in the north and south of the region. For the entire region, the temperature projection in the near future (at the end of twenty-first century) showed an increase of about 3 K/month wind speed and slows down generally in the north and south up to a factor of 0.6 ms1/month under both RCPs. However, when RFB was turned on, rainfall decreases by a factor 0.9 mm/month in the south and 0.8 mm/month in the north under RCP2.6 and 8.5, respectively. In summary, results show that elevated BC concentration in the atmosphere will lead to increase in temperature and decrease in rainfall in the near future relative to historical records and these changes could be exacerbated through BC interactive radiation feedback with the atmospheric variables.

Research areas: Atmospheric/Ocean Indicators
Arctic sea-ice loss intensifies aerosol transport to the Tibetan Plateau (2020)

The Tibetan Plateau (TP) has recently been polluted by anthropogenic emissions transported from South Asia, but the mechanisms conducive to this aerosol delivery are poorly understood. Here we show that winter loss of Arctic sea ice over the subpolar North Atlantic boosts aerosol transport toward the TP in April, when the aerosol loading is at its climatological maximum and preceding the Indian summer monsoon onset. Low sea ice in February weakens the polar jet, causing decreased Ural snowpack via reduced transport of warm, moist oceanic air into the high-latitude Eurasian interior. This diminished snowpack persists through April, reinforcing the Ural pressure ridge and East Asian trough, segments of a quasi-stationary Rossby wave train extending across Eurasia. These conditions facilitate an enhanced subtropical westerly jet at the southern edge of the TP, invigorating upslope winds that combine with mesoscale updrafts to waft emissions over the Himalayas onto the TP.

Research areas: Cryospheric Indicators, Atmospheric/Ocean Indicators
Spatiotemporal patterns of N2 fixation in coastal waters derived from rate measurements and remote sensing (2021)

Abstract. Coastal lagoons are important sites for nitrogen (N) removal via sediment burial and denitrification. Blooms of heterocystous cyanobacteria may diminish N retention as dinitrogen (N2) fixation offsets atmospheric losses via denitrification. We measured N2 fixation in the Curonian Lagoon, Europe's largest coastal lagoon, to better understand the factors controlling N2 fixation in the context of seasonal changes in phytoplankton community composition and external N inputs. Temporal patterns in N2 fixation were primarily determined by the abundance of heterocystous cyanobacteria, mainly Aphanizomenon flos-aquae, which became abundant after the decline in riverine nitrate inputs associated with snowmelt. Heterocystous cyanobacteria dominated the summer phytoplankton community resulting in strong correlations between chlorophyll a (Chl a) and N2 fixation. We used regression models relating N2 fixation to Chl a, along with remote-sensing-based estimates of Chl a to derive lagoon-scale estimates of N2 fixation. N2 fixation by pelagic cyanobacteria was found to be a significant component of the lagoon's N budget based on comparisons to previously derived fluxes associated with riverine inputs, sedimentwater exchange, and losses via denitrification. To our knowledge, this is the first study to derive ecosystem-scale estimates of N2 fixation by combining remote sensing of Chl a with empirical models relating N2 fixation rates to Chl a.

Research areas: Ecosystems
Spatial and temporal variability in dust storms in the Middle East, 20022018: three case studies in July 2009 (2021)

The Middle East is one of the most vulnerable regions to climate change and severe droughts. Climate change is associated with an increase of extreme weather frequency events across the globe. Climate change and droughts cause both severity and persistence dust storms in this area. In this study, the spatial and temporal variability of dust storms were characterized in the Middle East using satellite data (NDVI, TRMM, and AOD Aqua MODIS), synoptic station observation in Iran, and a numerical Weather Prediction for one dust event. The investigations of NDVI, precipitation rate, surface temperature, and AOD time series have shown that a significant increase in both surface temperature and AOD characterize this area from 2002 until 2018. While the rate of precipitation significantly declined, NDVI does not show specific trends because of its large variability and human influences. However, the study also showed a sharp decline in precipitation and consequently in vegetation cover in 2008, which caused a significant increase in both AOD and frequency of dust days in 2009. More than 100 dust days in five synoptic weather stations in the study area were observed in 2009. Also, this study shows that the number of dust storms has increased due to changes in governing atmospheric patterns over the area. The results (more than 100 dust days in five synoptic weather stations in the study area were observed for 1 year) showed both the effects of the earth surface respectively vegetation pattern changes (based on NDVI) and the atmospheric reasons (decline in precipitation) are the first time investigated in the study area. A numerical model simulation of three severe dust storms in July 2009 shows that dust emissions cover vast parts of the study area including east parts of Syria, Central Iraq, and northern and southern coasts of the Persian Gulf.

Research areas: Land Surface/Agriculture Indicators, Atmospheric/Ocean Indicators
Integrated Hydrologic and Hydraulic Analysis of Torrential Flood Hazard in Arequipa, Peru (2020)

Seated at the foot of the Misti volcano in an area prone to intense seasonal rains and earthquakes, the city of Arequipa is highly vulnerable to natural disasters. During the rainy season, intense storms create large volumes of runoff that rush through the city's ephemeral streams, known locally as torrenteras. Episodic flows in these torrenteras have caused flooding, damage to bridges, homes, and other infrastructure, and caused many deaths. In recent years, while unprecedented rain events have caused extreme disasters, the city's population has continued to expand into these channels by creating informal or illegal settlements. Currently, detailed hazard maps of flood-prone areas surrounding the torrenteras are not available to stakeholders in Arequipa. In this study, hydrologic and hydraulic models were combined to assess flash flood hazards, including inundation, velocity hazards, and slope instability hazards. Hydrologic models were created using satellite precipitation data and terrain-sensitive, gridded climate maps to characterize flow within six torrenteras in Arequipa. These flows were used in conjunction with elevation data and data collected in the field using an online mobile application system to develop a hydraulic model of these flood events. Hydraulic model outputs were used to determine flood hazards related to inundation, velocity affecting human stability, and slope instability in case study areas of the torrenteras. We then discuss how this information can be used by disaster risk management groups, water authorities, planners and municipalities, and community groups.

Research areas: Floods
Brown carbon light absorption over an urban environment in northern peninsular Southeast Asia (2021)

Light-absorbing organic carbon (or brown carbon, BrC) has been recognized as a critical driver in regional-to-global climate change on account of its significant contribution to light absorption. BrC sources vary from primary combustion processes (burning of biomass, biofuel, and fossil fuel) to secondary formation in the atmosphere. This paper investigated the light-absorbing properties of BrC such as site-specific mass absorption cross-section (MACBrC), absorption Angstrom exponent (AAEBrC), and the absorbing component of the refractive index (kBrC) by using light absorption measurements from a 7-wavelength aethalometer over an urban environment of Chiang Mai, Thailand in northern peninsular Southeast Asia (PSEA), from March to April 2016. The contribution of BrC to total aerosol absorption (mean  SD) was 46  9%, 29  7%, 24  6%, 20  4%, and 15  3% at 370, 470, 520, 590, and 660 nm, respectively, highlighting the significant influence of BrC absorption on the radiative imbalance over northern PSEA. Strong and significant associations between BrC light absorption and biomass-burning (BB) organic tracers highlighted the influence of primary BB emissions. The median MACBrC and kBrC values at 370 nm were 2.4 m2 g1 and 0.12, respectively. The fractional contribution of solar radiation absorbed by BrC relative to BC (mean  SD) in the 370950 nm range was estimated to be 34  7%, which can significantly influence the regional radiation budget and consequently atmospheric photochemistry. This study provides valuable information to understand BrC absorption over northern PSEA and can be used in model simulations to reassess the regional climatic impact with greater accuracy.

Research areas: Sun-Earth Interactions, Energy Production/Use, Environmental Impacts
Spatial-temporal variation characteristics of air pollution and apportionment of contributions by different sources in Shanxi province of China (2021)

With the implementation of the Air Pollution Prevention and Control Action Plan (APPCAP) since 2013, significant declines in pollutants concentrations have achieved in nationwide of China. However, as one of the major coal-production bases and intensive energy-consuming provinces in China, Shanxi has still been suffering from severe air quality problems in recent years. In this study, by combining a detailed bottom-up emission inventory and the weather research and forecasting (WRF) model/comprehensive air quality model with extensions (CAMx) model, the evolution of pollutant concentrations, source apportionment, and migration potentials from 2012 to 2015 in Shanxi are investigated. Estimated primary air pollutants emission declined significantly during 20122015. Compared with 2012, the simulated concentrations of PM2.5, PM10, SO2 and NO2 in January of 2015 are reduced by 24.7%, 24.1%, 23.0% and 18.0%, respectively. In contrast, heavy contaminated areas have shown negligible variations, which are highly concentrated in Taiyuan, Linfen, Jincheng, Changzhi, Lvliang, Yangquan and Jinzhong cities. In terms of contribution by source categories, the other industries and residential sources are identified as the most significant local contributors for PM2.5 and PM10, while SO2 and NO2 are mainly emitted by other industries and power plants. Scenarios analysis of 50% emission mitigation suggests that the emission reduction measures are generally more effective in summer than in winter. Moreover, the mitigation potential for each city varies from each other. These results indicate that more appropriate seasonal-specific emission reduction measures in each prefecture-level city should be implemented to further improve regional air quality and thus better protect public health.

Research areas: Air Quality, Energy Production/Use
Evaluation of black carbon estimations in global aerosol models (2009)

Abstract. We evaluate black carbon (BC) model predictions from the AeroCom model intercomparison project by considering the diversity among year 2000 model simulations and comparing model predictions with available measurements. These model-measurement intercomparisons include BC surface and aircraft concentrations, aerosol absorption optical depth (AAOD) retrievals from AERONET and Ozone Monitoring Instrument (OMI) and BC column estimations based on AERONET. In regions other than Asia, most models are biased high compared to surface concentration measurements. However compared with (column) AAOD or BC burden retreivals, the models are generally biased low. The average ratio of model to retrieved AAOD is less than 0.7 in South American and 0.6 in African biomass burning regions; both of these regions lack surface concentration measurements. In Asia the average model to observed ratio is 0.7 for AAOD and 0.5 for BC surface concentrations. Compared with aircraft measurements over the Americas at latitudes between 0 and 50N, the average model is a factor of 8 larger than observed, and most models exceed the measured BC standard deviation in the mid to upper troposphere. At higher latitudes the average model to aircraft BC ratio is 0.4 and models underestimate the observed BC loading in the lower and middle troposphere associated with springtime Arctic haze. Low model bias for AAOD but overestimation of surface and upper atmospheric BC concentrations at lower latitudes suggests that most models are underestimating BC absorption and should improve estimates for refractive index, particle size, and optical effects of BC coating. Retrieval uncertainties and/or differences with model diagnostic treatment may also contribute to the model-measurement disparity. Largest AeroCom model diversity occurred in northern Eurasia and the remote Arctic, regions influenced by anthropogenic sources. Changing emissions, aging, removal, or optical properties within a single model generated a smaller change in model predictions than the range represented by the full set of AeroCom models. Upper tropospheric concentrations of BC mass from the aircraft measurements are suggested to provide a unique new benchmark to test scavenging and vertical dispersion of BC in global models.

Research areas: Air Quality, Environmental Impacts
Spatiotemporal characteristics of aerosols and their trends over mainland China with the recent Collection 6 MODIS and OMI satellite datasets (2018)

With the rapid development of Chinas economy and high rate of industrialization, environmental pollution has become a major challenge for the country. The present study is aimed at analyzing spatiotemporal heterogeneities and changes in trends of different aerosol optical properties observed over China. To achieve this, Collection 6 Level 3 data retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS; 20022016) and Ozone Monitoring Instrument (OMI; 20052016) sensors were used to investigate aerosol optical depth (AOD550), Angstrm exponent (AE470660), and Absorption Aerosol Index (AAI). The spatial distribution of annual mean AOD550 was noticed to be high over economically and industrialized regions of the east, south, and northeast of China, while low aerosol loadings were located over rural and less-developed areas of the west and northeast of China. High AE470660 (> 1.0) values were characterized by the abundance of fine-mode particles and vice versa, likely attributed to large anthropogenic activities. Similarly, high AOD with corresponding high AE and low AAI was characterized over the urban-industrialized regions of the central, east, and south of China during most of the months, being more pronounced in June and July. On seasonal scale, AOD values were found to be high during spring, followed by the summer and autumn, and low during the winter season. It is also evident that all aerosol parameters showed a single-peak frequency distribution in all seasons over entire China. Further, the annual, monthly, and seasonal spatial trends revealed a decreasing trend in AOD over most regions of China, except in the southwest of China, which showed a positive increasing trend. Significant increasing trends were noted in AAI for all the seasons, particularly during autumn and winter, resulting in a large amount of the absorbing type of aerosols produced from biomass burning and desert dust.

Research areas: Air Quality, Environmental Impacts
A review of biomass burning: Emissions and impacts on air quality, health and climate in China (2017)

Biomass burning (BB) is a significant air pollution source, with global, regional and local impacts on air quality, public health and climate. Worldwide an extensive range of studies has been conducted on almost all the aspects of BB, including its specific types, on quantification of emissions and on assessing its various impacts. China is one of the countries where the significance of BB has been recognized, and a lot of research efforts devoted to investigate it, however, so far no systematic reviews were conducted to synthesize the information which has been emerging. Therefore the aim of this work was to comprehensively review most of the studies published on this topic in China, including literature concerning field measurements, laboratory studies and the impacts of BB indoors and outdoors in China. In addition, this review provides insights into the role of wildfire and anthropogenic BB on air quality and health globally. Further, we attempted to provide a basis for formulation of policies and regulations by policy makers in China.

Research areas: Environmental Impacts, Air Quality, Public Health