On the Segregation of Chemical Species in a Clear Boundary Layer Over Heterogeneous Surface Conditions

2013 ◽  
pp. 541-546
Author(s):  
Huug G. Ouwersloot ◽  
Jordi Vilà-Guerau de Arellano ◽  
Laurens N. Ganzeveld ◽  
Chiel C. van Heerwaarden ◽  
Maarten C. Krol ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Chemical Species ◽  
Heterogeneous Surface ◽  
Surface Conditions

scholarly journals On the segregation of chemical species in a clear boundary layer over heterogeneous land surfaces

2011 ◽  
Vol 11 (20) ◽  
pp. 10681-10704 ◽  
Author(s):  
H. G. Ouwersloot ◽  
J. Vilà-Guerau de Arellano ◽  
C. C. van Heerwaarden ◽  
L. N. Ganzeveld ◽  
M. C. Krol ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Chemical Reaction ◽  
Wind Direction ◽  
Rain Forest ◽  
Reaction Rates ◽  
Heterogeneous Surface ◽  
Background Wind ◽  
Homogeneous Surface ◽  
Surface Conditions ◽  
Chemical Reaction Rates

Abstract. Using a Large-Eddy Simulation model, we have systematically studied the inability of boundary layer turbulence to efficiently mix reactive species. This creates regions where the species are accumulated in a correlated or anti-correlated way, thereby modifying the mean reactivity. We quantify this modification by the intensity of segregation, IS, and analyse the driving mechanisms: heterogeneity of the surface moisture and heat fluxes, various background wind patterns and non-uniform isoprene emissions. The heterogeneous surface conditions are characterized by cool and wet forested patches with high isoprene emissions, alternated with warm and dry patches that represents pasture with relatively low isoprene emissions. For typical conditions in the Amazon rain forest, applying homogeneous surface forcings and in the absence of free tropospheric NOx, the isoprene-OH reaction rate is altered by less than 10%. This is substantially smaller than the previously assumed IS of 50% in recent large-scale model analyses of tropical rain forest chemistry. Spatial heterogeneous surface emissions enhance the segregation of species, leading to alterations of the chemical reaction rates up to 20%. The intensities of segregation are enhanced when the background wind direction is parallel to the borders between the patches and reduced in the case of a perpendicular wind direction. The effects of segregation on trace gas concentrations vary per species. For the highly reactive OH, the differences in concentration averaged over the boundary layer are less than 2% compared to homogeneous surface conditions, while the isoprene concentration is increased by as much as 12% due to the reduced chemical reaction rates. These processes take place at the sub-grid scale of chemistry transport models and therefore need to be parameterized.

scholarly journals The chemistry influencing ODEs in the Polar Boundary Layer in spring: a model study

2008 ◽  
Vol 8 (2) ◽  
pp. 7391-7453 ◽  
Author(s):  
M. Piot ◽  
R. von Glasow
Keyword(s):  
Boundary Layer ◽  
Ozone Depletion ◽  
Chemical Species ◽  
Field Measurements ◽  
The Arctic ◽  
Direct Reaction ◽  
Mixing Ratios ◽  
Model Study ◽  
Sensitivity Studies ◽  
Chemical Conditions

Abstract. Near-total depletions of ozone have been observed in the Arctic spring since the mid 1980s. The autocatalytic cycles involving reactive halogens are now recognized to be of main importance for Ozone Depletion Events (ODEs) in the Polar Boundary Layer (PBL). We present sensitivity studies using the model MISTRA in the box-model mode on the influence of chemical species on these ozone depletion processes. In order to test the sensitivity of the chemistry under polar conditions, we compared base runs undergoing fluxes of either Br2, BrCl, or Cl2 to induce ozone depletions, with similar runs including a modification of the chemical conditions. The role of HCHO, H2O2, DMS, Cl2, C2H4, C2H6, HONO, NO2, and RONO2 was investigated. Cases with elevated mixing ratios of HCHO, H2O2, DMS, Cl2, and HONO induced a shift in bromine speciation from Br/BrO to HOBr/HBr, while high mixing ratios of C2H6 induced a shift from HOBr/HBr to Br/BrO. Cases with elevated mixing ratios of HONO, NO2, and RONO2 induced a shift to BrNO2/BrONO2. The shifts from Br/BrO to HOBr/HBr accelerated the aerosol debromination, but also increased the total amount of deposited bromine at the surface (mainly via increased deposition of HOBr). These shifts to HOBr/HBr also hindered the BrO self-reaction. In these cases, the ozone depletion was slowed down, where increases in H2O2 and HONO had the greatest effect. The tests with increased mixing ratios of C2H4 highlighted the decrease in HOx which reduced the production of HOBr from bromine radicals. In addition, the direct reaction of C2H4 with bromine atoms led to less available reactive bromine. The aerosol debromination was therefore strongly reduced. Ozone levels were highly affected by the chemistry of C2H4. Cl2-induced ozone depletions were found unrealistic compared to field measurements due to the rapid production of CH3O2, HOx, and ROOH which rapidly convert reactive chlorine to HCl in a "chlorine counter-cycle". This counter-cycle efficiently reduces the concentration of reactive halogens in the boundary layer. Depending on the relative bromine and chlorine mixing ratios, the production of CH3O2, HOx, and ROOH from the counter-cycle can significantly affect the bromine chemistry. Therefore, the presence of both bromine and chlorine in the air may unexpectedly lead to a slow down in ozone destruction. For all NOy species studied (HONO, NO2, RONO2) the chemistry is characterized by an increased bromine deposition on snow reducing the amount of reactive bromine in the air. Ozone is less depleted under conditions of high mixing ratios of NOx. The production of HNO3 led to the acid displacement of HCl, and the release of chlorine out of salt aerosols (Cl2 or BrCl) increased.

scholarly journals Linking Meteorology, Turbulence, and Air Chemistry in the Amazon Rain Forest

2016 ◽  
Vol 97 (12) ◽  
pp. 2329-2342 ◽  
Author(s):  
Jose D. Fuentes ◽  
Marcelo Chamecki ◽  
Rosa Maria Nascimento dos Santos ◽  
Celso Von Randow ◽  
Paul C. Stoy ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Surface Layer ◽  
Vertical Distribution ◽  
Rain Forest ◽  
Forest Canopy ◽  
Cloud Condensation Nuclei ◽  
Chemical Species ◽  
Chemical Transformations ◽  
Condensation Nuclei ◽  
The Vertical Distribution

Abstract We describe the salient features of a field study whose goals are to quantify the vertical distribution of plant-emitted hydrocarbons and their contribution to aerosol and cloud condensation nuclei production above a central Amazonian rain forest. Using observing systems deployed on a 50-m meteorological tower, complemented with tethered balloon deployments, the vertical distribution of hydrocarbons and aerosols was determined under different boundary layer thermodynamic states. The rain forest emits sufficient reactive hydrocarbons, such as isoprene and monoterpenes, to provide precursors of secondary organic aerosols and cloud condensation nuclei. Mesoscale convective systems transport ozone from the middle troposphere, enriching the atmospheric boundary layer as well as the forest canopy and surface layer. Through multiple chemical transformations, the ozone-enriched atmospheric surface layer can oxidize rain forest–emitted hydrocarbons. One conclusion derived from the field studies is that the rain forest produces the necessary chemical species and in sufficient amounts to undergo oxidation and generate aerosols that subsequently activate into cloud condensation nuclei.

scholarly journals Characterization of a boreal convective boundary layer and its impact on atmospheric chemistry during HUMPPA-COPEC-2010

2012 ◽  
Vol 12 (19) ◽  
pp. 9335-9353 ◽  
Author(s):  
H. G. Ouwersloot ◽  
J. Vilà-Guerau de Arellano ◽  
A. C. Nölscher ◽  
M. C. Krol ◽  
L. N. Ganzeveld ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Chemistry ◽  
Convective Boundary Layer ◽  
Large Scale ◽  
Spatial Scales ◽  
Potential Temperature ◽  
Chemical Species ◽  
Convective Boundary ◽  
The Impact

Abstract. We studied the atmospheric boundary layer (ABL) dynamics and the impact on atmospheric chemistry during the HUMPPA-COPEC-2010 campaign. We used vertical profiles of potential temperature and specific moisture, obtained from 132 radio soundings, to determine the main boundary layer characteristics during the campaign. We propose a classification according to several main ABL prototypes. Further, we performed a case study of a single day, focusing on the convective boundary layer, to analyse the influence of the dynamics on the chemical evolution of the ABL. We used a mixed layer model, initialized and constrained by observations. In particular, we investigated the role of large scale atmospheric dynamics (subsidence and advection) on the ABL development and the evolution of chemical species concentrations. We find that, if the large scale forcings are taken into account, the ABL dynamics are represented satisfactorily. Subsequently, we studied the impact of mixing with a residual layer aloft during the morning transition on atmospheric chemistry. The time evolution of NOx and O3 concentrations, including morning peaks, can be explained and accurately simulated by incorporating the transition of the ABL dynamics from night to day. We demonstrate the importance of the ABL height evolution for the representation of atmospheric chemistry. Our findings underscore the need to couple the dynamics and chemistry at different spatial scales (from turbulence to mesoscale) in chemistry-transport models and in the interpretation of observational data.

scholarly journals What do we learn on bromoform transport and chemistry in deep convection from fine scale modelling?

2011 ◽  
Vol 11 (11) ◽  
pp. 29561-29600 ◽  
Author(s):  
V. Marécal ◽  
M. Pirre ◽  
G. Krysztofiak ◽  
B. Josse
Keyword(s):  
Boundary Layer ◽  
Transport Model ◽  
Deep Convection ◽  
Chemical Species ◽  
Convective Cloud ◽  
Initial Boundary ◽  
Mixing Ratio ◽  
Atmospheric Conditions ◽  
Upper Troposphere ◽  
Soluble Species

Abstract. Bromoform is one of the main sources of halogenated Very Short-Lived Species (VSLS) that possibly contributes when degradated to the inorganic halogen loading in the stratosphere. Because of its short lifetime of about four weeks, its pathway to the stratosphere is mainly the transport by convection up to the tropical tropopause layer (TTL) and then by radiative ascent in the low stratosphere. Some of its degradation product gases (PGs) that are soluble can be scavenged and not reach the TTL. In this paper we present a detailed modelling study of the transport and the degradation of bromoform and its PGs in convection. We use a 3-D-cloud resolving model coupled with a chemistry model including gaseous and aqueous chemistry. We run idealised simulations up to 10 days, initialised using a tropical radiosounding for atmospheric conditions and using outputs from a global chemistry-transport model for chemical species. Bromoform is initialised only in the low levels. The first simulation is run with stable atmospheric conditions. It shows that the sum of the bromoform and its PGs significantly decreases with time because of dry deposition and that PGs are mainly in the form of HBr after 2 days of simulation. The other simulation is similar to the first simulation but includes perturbations of temperature and of moisture leading to the development of a convective cloud reaching the TTL. Results of this simulation show an efficient vertical transport of the bromoform from the boundary layer in the upper troposphere and TTL (mixing ratio up to 45% of the initial boundary layer mixing ratio). The organic PGs, which are for the most abundant of them not very soluble, are also uplifted efficiently. For the inorganic PGs, which are more abundant than organic PGs, their mixing ratios in the upper troposphere and in the TTL depend on the partitioning between inorganic soluble and inorganic non soluble species in the convective cloud. Important soluble species such as HBr and HOBr are efficiently scavenged by rain. This removal is reduced by the production of Br2 (not soluble) in the gas phase from aqueous processes in the cloud droplets. This Br2 production process is therefore important for the PG budget in the upper troposphere and in the TTL. We also showed that this process is favoured by acidic conditions in the coud droplets, i.e. polluted conditions.

scholarly journals Combined effects of surface conditions, boundary layer dynamics and chemistry on diurnal SOA-evolution

2012 ◽  
Vol 12 (4) ◽  
pp. 9331-9375 ◽  
Author(s):  
R. H. H. Janssen ◽  
J. Vilà-Guerau de Arellano ◽  
L. N. Ganzeveld ◽  
P. Kabat ◽  
J. L. Jimenez ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Atmospheric Boundary Layer ◽  
Land Surface ◽  
Large Scale ◽  
Organic Aerosol ◽  
Layer Growth ◽  
Combined Effects ◽  
Free Troposphere ◽  
Surface Conditions ◽  
Boundary Layer Dynamics

Abstract. We study the combined effects of land surface conditions, atmospheric boundary layer dynamics and chemistry on the diurnal evolution of biogenic secondary organic aerosol in the atmospheric boundary layer, using a model that contains the essentials of all these components. First, we evaluate the model for a case study in Hyytiälä, Finland, and find that it is able to well reproduce the observed dynamics and gas-phase chemistry. We show that the exchange of organic aerosol between the free troposphere and the boundary layer (entrainment) must be taken into account in order to explain the observed diurnal cycle in organic aerosol (OA) concentration. An examination of the budgets of organic aerosol and terpene concentration shows that the former is dominated by entrainment, while the latter is mainly driven by emission and chemical transformation. We systematically examine the role of the land surface, which governs both the surface energy balance partitioning and terpene-emissions, and the large-scale atmospheric process of vertical subsidence. Entrainment is especially important for the dilution of organic aerosol concentrations under conditions of dry soils and low terpene-emissions. Subsidence suppresses boundary layer growth while enhancing entrainment. Therefore it influences the relationship between organic aerosol and terpene-concentrations. Our findings indicate that the diurnal evolution of SOA in the boundary layer is the result of coupled effects of the land surface, dynamics of the atmospheric boundary layer, chemistry, and free troposphere conditions. This has potentially some consequences for the design of both field campaigns and large-scale modeling studies.

scholarly journals Surface heterogeneity impacts on boundary layer dynamics via energy balance partitioning

2010 ◽  
Vol 10 (7) ◽  
pp. 17815-17851 ◽  
Author(s):  
N. A. Brunsell ◽  
D. B. Mechem ◽  
M. C. Anderson
Keyword(s):  
Boundary Layer ◽  
Heat Flux ◽  
Latent Heat ◽  
Latent Heat Flux ◽  
Land Surface ◽  
Surface Heterogeneity ◽  
Length Scales ◽  
Surface Conditions ◽  
Boundary Layer Dynamics

Abstract. The role of land-atmosphere interactions under heterogeneous surface conditions is investigated in order to identify mechanisms responsible for altering surface heat and moisture fluxes. Twelve coupled land surface – large eddy simulation scenarios with four different length scales of surface variability under three different horizontal wind speeds are used in the analysis. The base case uses Landsat ETM imagery over the Cloud Land Surface Interaction Campaign (CLASIC) field site for 3 June 2007. Using wavelets, the surface fields are band-pass filtered in order to maintain the spatial mean and variances to length scales of 200 m, 1600 m, and 12.8 km as lower boundary conditions to the model. The simulations exhibit little variation in net radiation. Rather, a change in the partitioning of the surface energy between sensible and latent heat flux is responsible for differences in boundary layer dynamics. The sensible heat flux is dominant for intermediate surface length scales. For smaller and larger scales of surface heterogeneity, which can be viewed as being more homogeneous, the latent heat flux becomes increasingly important. The results reflect a general decrease of the Bowen ratio as the surface conditions transition from heterogeneous to homogeneous. Air temperature is less sensitive to surface heterogeneity than water vapor, which implies that the role of surface heterogeneity in modifying the local temperature gradients in order to maximize convective heat fluxes. More homogeneous surface conditions, on the other hand, tend to maximize latent heat flux. Scalar vertical profiles respond predictably to the partitioning of surface energy. Fourier spectra of the vertical wind speed, air temperature and specific humidity (w, T and q) and associated cospectra (w'T', w'q' and T'q'), however, are insensitive to the length scale of surface heterogeneity, but the near surface spectra are sensitive to the mean wind speed.

scholarly journals Missing OH reactivity in the global marine boundary layer

2020 ◽  
Vol 20 (6) ◽  
pp. 4013-4029 ◽  
Author(s):  
Alexander B. Thames ◽  
William H. Brune ◽  
David O. Miller ◽  
Hannah M. Allen ◽  
Eric C. Apel ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Dimethyl Sulfide ◽  
Marine Boundary Layer ◽  
Limit Of Detection ◽  
Chemical Species ◽  
Volatile Organic ◽  
The Mean ◽  
The Difference

Abstract. The hydroxyl radical (OH) reacts with thousands of chemical species in the atmosphere, initiating their removal and the chemical reaction sequences that produce ozone, secondary aerosols, and gas-phase acids. OH reactivity, which is the inverse of OH lifetime, influences the OH abundance and the ability of OH to cleanse the atmosphere. The NASA Atmospheric Tomography (ATom) campaign used instruments on the NASA DC-8 aircraft to measure OH reactivity and more than 100 trace chemical species. ATom presented a unique opportunity to test the completeness of the OH reactivity calculated from the chemical species measurements by comparing it to the measured OH reactivity over two oceans across four seasons. Although the calculated OH reactivity was below the limit of detection for the ATom instrument used to measure OH reactivity throughout much of the free troposphere, the instrument was able to measure the OH reactivity in and just above the marine boundary layer. The mean measured value of OH reactivity in the marine boundary layer across all latitudes and all ATom deployments was 1.9 s−1, which is 0.5 s−1 larger than the mean calculated OH reactivity. The missing OH reactivity, the difference between the measured and calculated OH reactivity, varied between 0 and 3.5 s−1, with the highest values over the Northern Hemisphere Pacific Ocean. Correlations of missing OH reactivity with formaldehyde, dimethyl sulfide, butanal, and sea surface temperature suggest the presence of unmeasured or unknown volatile organic compounds or oxygenated volatile organic compounds associated with ocean emissions.

Sign in / Sign up

Export Citation Format

Share Document