201 research outputs found
Ammonia emissions from beech forest after leaf fall – measurements and modelling
Get PDFAbstract. The understanding of biochemical feed-back mechanisms in the climate system is lacking knowledge in relation to bi-directional ammonia (NH3) exchange between natural ecosystems and the atmosphere. We therefore study the atmospheric NH3 fluxes during a 25 days period during autumn 2010 (21 October–15 November) for the Danish beech forest, Lille Bøgeskov, to address the hypothesis that NH3 emissions occur from deciduous forests in relation to leaf fall. This is accomplished by using observations of vegetation status, NH3 fluxes and model calculations. Vegetation status was observed using plant area index (PAI) and leaf area index (LAI). NH3 fluxes were measured using the relaxed eddy accumulation (REA) method. The REA based NH3 concentrations were compared to NH3 denuder measurements. Model calculations were obtained with the Danish Ammonia MOdelling System (DAMOS). 57.7% of the fluxes measured showed emission and 19.5% showed deposition. The mean NH3 flux was 0.087 ± 0.19 μg NH3-N m−2 s−1. A clear tendency of the flux going from negative (deposition) to positive (emission) fluxes of up to 0.96 ± 0.40 μg NH3-N m−2 s−1 throughout the measurement period was found. In the leaf fall period (23 October–8 November), an increase in the atmospheric NH3 concentrations was related to the increasing forest NH3 flux. The modelled concentration from DAMOS fits well the measured concentrations before leaf fall. During and after leaf fall, the modelled concentrations are too low. The results indicate that the missing contribution to atmospheric NH3 concentration from vegetative surfaces related to leaf fall are of a relatively large magnitude. We therefore conclude that emissions from deciduous forests are important to include in model calculations of atmospheric NH3 for forest ecosystems. Finally, diurnal variations in the measured NH3 concentrations were related to meteorological conditions, forest phenology and the spatial distribution of local anthropogenic NH3 sources. This suggests that an accurate description of ammonia fluxes over forest ecosystems requires a dynamic description of atmospheric and vegetation processes.
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The Effect of Seasonal Priming on Specific Inhalation Challenges With Birch and Grass Allergen Among Persons With Allergic Rhinitis
Get PDFUrban vertical air pollution gradient and dynamics investigated with low-cost sensors and large-eddy simulations
Get PDFA network of five low-cost air pollution sensor (LCS) nodes was deployed vertically on the exterior of the H. C. Ørsted Institute at the University of Copenhagen, Denmark, to investigate the transport of pollution from the road below. All LCS nodes measured PM2.5, NO2, and O3 at 1-min time resolution, and one of them also measured noise. Traffic was monitored with a webcam, where traffic type and levels were derived using a machine-learning algorithm. We investigated how well traffic-related air pollution, noise, and real-time traffic counts serve as proxies for one another. The correlations between NO2, noise, and traffic count exhibited relatively low values when considering all the data. However, these correlations significantly increased under southwesterly wind direction and low wind speed, reaching R2 = 0.40 for NO2 and noise, R2 = 0.51 for NO2 and traffic volume, and R2 = 0.70 for noise and traffic volume. These results indicate a common source, namely traffic, for all three parameters. The five LCS nodes spanning 25 m vertically had extremely low intervariability with minimum R2-values of 0.98 for PM2.5, 0.89 for NO2, and 0.97 for O3. The system could not detect a vertical gradient in pollution levels. Large-eddy simulation model runs using the PALM model system generally supported the lack of gradient observed in measured observations. Under slightly unstable stratification, concentration remained relatively constant with height for southwesterly and southerly winds. Conversely, winds from the north, west, and northwest showed an increase in concentration with height. For other wind directions, the concentration decreased with height by approximately 40 % to 50 %, which is not as strong as for neutral stratification, attributed to enhanced vertical mixing under unstable stratification. Based on the measurements and modeling, we conclude that the vertical concentration profile is very sensitive to stratification, and under these conditions, the concentration outside the window of a fifth-floor office is almost the same as for an office on the ground floor
Betydningen af partikelfiltre for luftkvalitet og sundhedseffekter
Get PDFKonsekvenser for emission, luftkvalitet, befolkningseksponering og sundhedseffekter af montering af partikelfiltre med en effektivitet på 80% på alle tunge dieselkøretøjer i Danmark er vurderet pba. eksisterende data. Sundhedsmæssige vurderinger er baseret på en metode udviklet af WHO, som tager udgangspunkt i PM10 i bybaggrundsluften. Beregningerne, der er behæftet med meget stor usikkerhed, viser at forureningen med PM10 kun reduceres lidt (skønsmæssigt omkring 2%) i byernes baggrunds- luft. Den beskedne reduktion skyldes, at en meget stor del af denne forurening er regional, d.v.s fra hele Europa, samt at dieselpartikler hovedsageligt er ultrafine med meget lav masse. De sundhedsmæssige gevinster bliver derfor tilsyneladende beskedne. Beregningerne med WHO’s metode resulterer således kun i en reduktion på 22 for tidligere dødsfald, som kunne spares ved montering af filtre. Imidlertid mistænkes de ultrafine partikler i dieselemission for at være ansvarlige for en væsentlig del af de partikelrelaterede helbredseffekter, og de ultrafine partikler reduceres med omkring 1/3 ved montering af filtre. Derfor må helbredseffekten antages at underestimeres ved den anvendte WHO metode
Measuring and modelling dry deposition of ammonia to deciduous forest using high temporal and spatial resolution techniques
Get PDFMiljøzoner, partikler og sundhed
Get PDFPartikler fra tunge køretøjer er en af de mest sundhedsskadelige emissioner fra trafikken. Det er i dag teknisk muligt på en lastbil at montere et partikelfilter, som reducerer partikelemissionen med helt op til 80%. Det er imidlertid forholdsvis dyrt, og det vil ikke være samfundsøkonomisk rentabelt at montere filtre på hele den danske lastbilpark.I stedet kan man målrette et krav om brug af partikelfiltre til centrale byområder, hvor befolkningens eksponering - og dermed den sundhedsmæssige skade - er størst. Dette kan gøres i form af miljøzoner, som er zoner, hvor der gælder særlige regler for trafikken begrundet i miljøhensyn. Konsekvenserne af at indføre sådanne miljøzoner er vurderet for tre case-byer - København, Aalborg og Vejle - og på baggrund af dette er der foretaget en vurdering af konsekvenserne for henholdsvis de 4 og de 10 største byer i Danmark. Konsekvenserne omfatter økonomi, trafik og sundhed, og desuden beskrives de mere holdningsprægede konsekvenser for bilejerne
A Parameter Estimation and Identifiability Analysis Methodology Applied to a Street Canyon Air Pollution Model
Get PDFMathematical models are increasingly used in environmental science thus increasing
the importance of uncertainty and sensitivity analyses. In the present
study, an iterative parameter estimation and identifiability analysis methodology
is applied to an atmospheric model – the Operational Street Pollution Model
(OSPMr). To assess the predictive validity of the model, the data is split into
an estimation and a prediction data set using two data splitting approaches and
data preparation techniques (clustering and outlier detection) are analysed. The
sensitivity analysis, being part of the identifiability analysis, showed that some
model parameters were significantly more sensitive than others. The application
of the determined optimal parameter values was shown to succesfully equilibrate
the model biases among the individual streets and species. It was as well shown
that the frequentist approach applied for the uncertainty calculations underestimated
the parameter uncertainties. The model parameter uncertainty was
qualitatively assessed to be significant, and reduction strategies were identified
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