Atmospheric oxidation in the presence of clouds during the Deep Convective Clouds and Chemistry (DC3) study

Abstract. Deep convective clouds are critically important to the distribution of atmospheric constituents throughout the troposphere but are difficult environments to study. The Deep Convective Clouds and Chemistry (DC3) study in 2012 provided the environment, platforms, and instrumentation to test oxidation chemistry around deep convective clouds and their impacts downwind. Measurements on the NASA DC-8 aircraft included those of the radicals hydroxyl (OH) and hydroperoxyl (HO2), OH reactivity, and more than 100 other chemical species and atmospheric properties. OH, HO2, and OH reactivity were compared to photochemical models, some with and some without simplified heterogeneous chemistry, to test the understanding of atmospheric oxidation as encoded in the model. In general, the agreement between the observed and modeled OH, HO2, and OH reactivity was within the combined uncertainties for the model without heterogeneous chemistry and the model including heterogeneous chemistry with small OH and HO2 uptake consistent with laboratory studies. This agreement is generally independent of the altitude, ozone photolysis rate, nitric oxide and ozone abundances, modeled OH reactivity, and aerosol and ice surface area. For a sunrise to midday flight downwind of a nighttime mesoscale convective system, the observed ozone increase is consistent with the calculated ozone production rate. Even with some observed-to-modeled discrepancies, these results provide evidence that a current measurement-constrained photochemical model can simulate observed atmospheric oxidation processes to within combined uncertainties, even around convective clouds. For this DC3 study, reduction in the combined uncertainties would be needed to confidently unmask errors or omissions in the model chemical mechanism.

Download Full-text

Atmospheric Oxidation in the Presence of Clouds during the Deep Convective Clouds and Chemistry (DC3) Study

10.5194/acp-2018-120 ◽

2018 ◽

Author(s):

William H. Brune ◽

Xinrong Ren ◽

Li Zhang ◽

Jinqiu Mao ◽

David O. Miller ◽

...

Keyword(s):

Chemical Species ◽

Mesoscale Convective System ◽

Ozone Production ◽

Atmospheric Oxidation ◽

Convective System ◽

Heterogeneous Chemistry ◽

Convective Clouds ◽

Deep Convective Clouds ◽

Oxidation Chemistry ◽

Photochemical Models

Abstract. Deep convective clouds are critically important to the distribution of atmospheric constituents throughout the troposphere but are difficult environments to study. The Deep Convective Clouds and Chemistry (DC3) study provided the environment, platforms, and instrumentation to test oxidation chemistry around deep convective clouds and their impacts downwind. Measurements on the NASA DC-8 aircraft included those of hydroxyl (OH), hydroperoxyl (HO2), OH reactivity, and more than 100 other chemical species and atmospheric properties. OH, HO2, and OH reactivity were compared to photochemical models, some with and some without simplified heterogeneous chemistry, to test the understanding of atmospheric oxidation as encoded in the model. In general, the agreement between the observed and modeled OH, HO2, and OH reactivity were all well within the combined uncertainties for both the model without heterogeneous chemistry and the model that includes heterogeneous chemistry with small OH and HO2 uptake consistent with laboratory studies. This agreement is generally independent of the altitude, ozone photolysis rate, nitric oxide and ozone abundances, modeled OH reactivity, and aerosol and ice surface area. For a sunrise to midday flight downwind of a nighttime mesoscale convective system, the observed ozone increase is consistent with the calculated ozone production rate. Even with some observed-to-modeled discrepancies, these results provide evidence that current photochemical models, properly constrained with measurements, can generally simulate observed atmospheric oxidation processes even around clouds.

Download Full-text

Effect of Aerosol on Circulations and Precipitation in Deep Convective Clouds

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-11-0111.1 ◽

2012 ◽

Vol 69 (6) ◽

pp. 1957-1974 ◽

Cited By ~ 27

Author(s):

Seoung Soo Lee

Keyword(s):

Mesoscale Convective System ◽

Cloud System ◽

Convective System ◽

Entire Domain ◽

Convective Clouds ◽

Deep Convective Clouds ◽

Mesoscale Convective

Abstract This study examines the effect of a mesoscale perturbation of aerosol on a larger-scale cloud system driven by deep convective clouds. An aerosol-perturbed domain of size 120 km is prescribed in the middle of the larger-scale domain of size 1100 km. Aerosol perturbations in the mesoscale domain result in an intensification of convection in a mesoscale convective system (MCS). This leads to an intensification of the larger-scale circulations, which in turn leads to an intensification of the larger-scale subsidence. While the invigorated convection enhances precipitation in the MCS, the intensified larger-scale subsidence acts to increase the larger-scale stability and thus to suppress convection and precipitation in the larger-scale domain. The suppression of precipitation in the larger-scale domain outweighs the enhancement of precipitation in the mesoscale domain, leading to suppressed precipitation over the entire domain. The ramifications of aerosol perturbations therefore need to be considered on scales much larger than the scale of the perturbation.

Download Full-text

Testing Atmospheric Oxidation in an Alabama Forest

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-16-0044.1 ◽

2016 ◽

Vol 73 (12) ◽

pp. 4699-4710 ◽

Cited By ~ 31

Author(s):

Philip A. Feiner ◽

William H. Brune ◽

David O. Miller ◽

Li Zhang ◽

Ronald C. Cohen ◽

...

Keyword(s):

Current Model ◽

Chemical Species ◽

Chemical Mechanism ◽

Atmospheric Oxidation ◽

Good Test ◽

Chemical Mechanisms ◽

Volatile Organic ◽

Master Chemical Mechanism ◽

The Difference ◽

Oxidation Chemistry

Abstract The chemical species emitted by forests create complex atmospheric oxidation chemistry and influence global atmospheric oxidation capacity and climate. The Southern Oxidant and Aerosol Study (SOAS) provided an opportunity to test the oxidation chemistry in a forest where isoprene is the dominant biogenic volatile organic compound. Hydroxyl (OH) and hydroperoxyl (HO2) radicals were two of the hundreds of atmospheric chemical species measured, as was OH reactivity (the inverse of the OH lifetime). OH was measured by laser-induced fluorescence (LIF) and by taking the difference in signals without and with an OH scavenger that was added just outside the instrument’s pinhole inlet. To test whether the chemistry at SOAS can be simulated by current model mechanisms, OH and HO2 were evaluated with a box model using two chemical mechanisms: Master Chemical Mechanism, version 3.2 (MCMv3.2), augmented with explicit isoprene chemistry and MCMv3.3.1. Measured and modeled OH peak at about 106 cm−3 and agree well within combined uncertainties. Measured and modeled HO2 peak at about 27 pptv and also agree well within combined uncertainties. Median OH reactivity cycled between about 11 s−1 at dawn and about 26 s−1 during midafternoon. A good test of the oxidation chemistry is the balance between OH production and loss rates using measurements; this balance was observed to within uncertainties. These SOAS results provide strong evidence that the current isoprene mechanisms are consistent with measured OH and HO2 and, thus, capture significant aspects of the atmospheric oxidation chemistry in this isoprene-rich forest.

Download Full-text

Tropical deep convective life cycle: Cb-anvil cloud microphysics from high-altitude aircraft observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-13223-2014 ◽

2014 ◽

Vol 14 (23) ◽

pp. 13223-13240 ◽

Cited By ~ 12

Author(s):

W. Frey ◽

S. Borrmann ◽

F. Fierli ◽

R. Weigel ◽

V. Mitev ◽

...

Keyword(s):

Life Cycle ◽

High Altitude ◽

Potential Temperature ◽

Cloud Microphysics ◽

Mature Stage ◽

Convective System ◽

Ice Crystal ◽

Convective Clouds ◽

Tropical Tropopause ◽

Deep Convective Clouds

Abstract. The case study presented here focuses on the life cycle of clouds in the anvil region of a tropical deep convective system. During the SCOUT-O3 campaign from Darwin, Northern Australia, the Hector storm system has been probed by the Geophysica high-altitude aircraft. Clouds were observed by in situ particle probes, a backscatter sonde, and a miniature lidar. Additionally, aerosol number concentrations have been measured. On 30 November 2005 a double flight took place and Hector was probed throughout its life cycle in its developing, mature, and dissipating stage. The two flights were four hours apart and focused on the anvil region of Hector in altitudes between 10.5 and 18.8 km (i.e. above 350 K potential temperature). Trajectory calculations, satellite imagery, and ozone measurements have been used to ensure that the same cloud air masses have been probed in both flights. The size distributions derived from the measurements show a change not only with increasing altitude but also with the evolution of Hector. Clearly different cloud to aerosol particle ratios as well as varying ice crystal morphology have been found for the different development stages of Hector, indicating different freezing mechanisms. The development phase exhibits the smallest ice particles (up to 300 μm) with a rather uniform morphology. This is indicative for rapid glaciation during Hector's development. Sizes of ice crystals are largest in the mature stage (larger than 1.6 mm) and even exceed those of some continental tropical deep convective clouds, also in their number concentrations. The backscatter properties and particle images show a change in ice crystal shape from the developing phase to rimed and aggregated particles in the mature and dissipating stages; the specific shape of particles in the developing phase cannot be distinguished from the measurements. Although optically thin, the clouds in the dissipating stage have a large vertical extent (roughly 6 km) and persist for at least 6 h. Thus, the anvils of these high-reaching deep convective clouds have a high potential for affecting the tropical tropopause layer by modifying the humidity and radiative budget, as well as for providing favourable conditions for subvisible cirrus formation. The involved processes may also influence the amount of water vapour that ultimately reaches the stratosphere in the tropics.

Download Full-text

Automated sequence analysis of atmospheric oxidation pathways: SEQUENCE version 1.0

Geoscientific Model Development ◽

10.5194/gmd-2-145-2009 ◽

2009 ◽

Vol 2 (2) ◽

pp. 145-152

Author(s):

T. M. Butler

Keyword(s):

Sequence Analysis ◽

Sequential Analysis ◽

Chemical Species ◽

Ozone Production ◽

Atmospheric Oxidation ◽

Product Yields ◽

Intermediate Products ◽

Photochemical Model ◽

Detailed Picture

Abstract. An algorithm for the sequential analysis of the atmospheric oxidation of chemical species using output from a photochemical model is presented. Starting at a "root species", the algorithm traverses all possible reaction sequences which consume this species, and lead, via intermediate products, to final products. The algorithm keeps track of the effects of all of these reactions on their respective reactants and products. Upon completion, the algorithm has built a detailed picture of the effects of the oxidation of the root species on its chemical surroundings. The output of the algorithm can be used to determine product yields, radical recycling fractions, and ozone production potentials of arbitrary chemical species.

Download Full-text

Global tropospheric effects of aromatic chemistry with the SAPRC-11 mechanism implemented in GEOS-Chem

10.5194/gmd-2018-196 ◽

2018 ◽

Cited By ~ 1

Author(s):

Yingying Yan ◽

David Cabrera-Perez ◽

Jintai Lin ◽

Andrea Pozzer ◽

Lu Hu ◽

...

Keyword(s):

Production Efficiency ◽

Chemical Species ◽

Oxidation Products ◽

Chemical Mechanism ◽

Ozone Production ◽

Peroxy Radicals ◽

Mixing Ratios ◽

Regional Effects ◽

Source Regions ◽

Remote Troposphere

Abstract. The GEOS-Chem model has been updated with the SAPRC-11 aromatics chemical mechanism, with the purpose of evaluating global and regional effects of the most abundant aromatics (benzene, toluene, xylenes) on the chemical species important for tropospheric oxidation capacity. The model evaluation based on surface and aircraft observations indicates good agreement for aromatics and ozone. A comparison between scenarios in GEOS-Chem with simplified aromatic chemistry (as in the standard setup, with no ozone formation from related peroxy radicals or recycling of NOx) and with the SAPRC-11 scheme reveals relatively slight changes in ozone, hydroxyl radical, and nitrogen oxides on a global mean basis (1–4 %), although remarkable regional differences (5–20 %) exist near the source regions. NOx decreases over the source regions and increases in the remote troposphere, due mainly to more efficient transport of peroxyacetyl nitrate (PAN), which is increased with the SAPRC aromatic chemistry. Model ozone mixing ratios with the updated aromatic chemistry increase by up to 5 ppb (more than 10 %), especially in industrially polluted regions. The ozone change is partly due to the direct influence of aromatic oxidation products on ozone production rates, and in part to the altered spatial distribution of NOx that enhances the tropospheric ozone production efficiency. Improved representation of aromatics is important to simulate the tropospheric oxidation.

Download Full-text

Global tropospheric effects of aromatic chemistry with the SAPRC-11 mechanism implemented in GEOS-Chem version 9-02

Geoscientific Model Development ◽

10.5194/gmd-12-111-2019 ◽

2019 ◽

Vol 12 (1) ◽

pp. 111-130 ◽

Cited By ~ 2

Author(s):

Yingying Yan ◽

David Cabrera-Perez ◽

Jintai Lin ◽

Andrea Pozzer ◽

Lu Hu ◽

...

Keyword(s):

Production Efficiency ◽

Chemical Species ◽

Oxidation Products ◽

Chemical Mechanism ◽

Ozone Production ◽

Peroxy Radicals ◽

Mixing Ratios ◽

Earth Observing System ◽

Source Regions ◽

Remote Troposphere

Abstract. The Goddard Earth Observing System with chemistry (GEOS-Chem) model has been updated with the State-wide Air Pollution Research Center version 11 (SAPRC-11) aromatics chemical mechanism, with the purpose of evaluating global and regional effects of the most abundant aromatics (benzene, toluene, xylenes) on the chemical species important for tropospheric oxidation capacity. The model evaluation based on surface and aircraft observations indicates good agreement for aromatics and ozone. A comparison between scenarios in GEOS-Chem with simplified aromatic chemistry (as in the standard setup, with no ozone formation from related peroxy radicals or recycling of NOx) and with the SAPRC-11 scheme reveals relatively slight changes in ozone, the hydroxyl radical, and nitrogen oxides on a global mean basis (1 %–4 %), although remarkable regional differences (5 %–20 %) exist near the source regions. NOx decreases over the source regions and increases in the remote troposphere, due mainly to more efficient transport of peroxyacetyl nitrate (PAN), which is increased with the SAPRC aromatic chemistry. Model ozone mixing ratios with the updated aromatic chemistry increase by up to 5 ppb (more than 10 %), especially in industrially polluted regions. The ozone change is partly due to the direct influence of aromatic oxidation products on ozone production rates, and in part to the altered spatial distribution of NOx that enhances the tropospheric ozone production efficiency. Improved representation of aromatics is important to simulate the tropospheric oxidation.

Download Full-text

Sensitivity of aerosol and cloud effects on radiation to cloud types: comparison between deep convective clouds and warm stratiform clouds over one-day period

Atmospheric Chemistry and Physics ◽

10.5194/acp-9-2555-2009 ◽

2009 ◽

Vol 9 (7) ◽

pp. 2555-2575 ◽

Cited By ~ 25

Author(s):

S. S. Lee ◽

L. J. Donner ◽

V. T. J. Phillips

Keyword(s):

Mesoscale Convective System ◽

Convective System ◽

Ice Clouds ◽

Cloud Forcing ◽

Convective Clouds ◽

Lower Cloud ◽

Stratiform Clouds ◽

Stratocumulus Clouds ◽

Mesoscale Convective ◽

Aerosol Effects

Abstract. Cloud and aerosol effects on radiation in two contrasting cloud types, a deep mesoscale convective system (MCS) and warm stratocumulus clouds, are simulated and compared. At the top of the atmosphere, 45–81% of shortwave cloud forcing (SCF) is offset by longwave cloud forcing (LCF) in the MCS, whereas warm stratiform clouds show the offset of less than ~20%. 28% of increased negative SCF is offset by increased LCF with increasing aerosols in the MCS at the top of the atmosphere. However, the stratiform clouds show the offset of just around 2–5%. Ice clouds as well as liquid clouds play an important role in the larger offset in the MCS. Lower cloud-top height and cloud depth, characterizing cloud types, lead to the smaller offset of SCF by LCF and the offset of increased negative SCF by increased LCF at high aerosol in stratocumulus clouds than in the MCS. Supplementary simulations show that this dependence of modulation of LCF on cloud depth and cloud-top height is also simulated among different types of convective clouds.

Download Full-text

Coupling of HO<sub>x</sub>, NO<sub>x</sub> and halogen chemistry in the Antarctic boundary layer

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-10-15109-2010 ◽

2010 ◽

Vol 10 (6) ◽

pp. 15109-15165 ◽

Cited By ~ 1

Author(s):

W. J. Bloss ◽

M. Camredon ◽

J. D. Lee ◽

D. E. Heard ◽

J. M. C. Plane ◽

...

Keyword(s):

Boundary Layer ◽

Layer Structure ◽

Chemical Species ◽

Austral Summer ◽

Chemical Mechanism ◽

Ozone Production ◽

Physical Parameters ◽

Research Station ◽

Antarctic Boundary Layer ◽

The Antarctic

Abstract. A modelling study of radical chemistry in the coastal Antarctic boundary layer, based upon observations performed in the course of the CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) campaign at Halley Research Station in coastal Antarctica during the austral summer 2004/2005, is described: a detailed zero-dimensional photochemical box model was used, employing inorganic and organic reaction schemes drawn from the Master Chemical Mechanism, with additional halogen (iodine and bromine) reactions added. The model was constrained to observations of long-lived chemical species, measured photolysis rates and meteorological parameters, and the simulated levels of HOx, NOx and XO compared with those observed. The model was able to replicate the mean levels and diurnal variation in the halogen oxides IO and BrO, and to reproduce NOx levels and speciation very well. The NOx source term implemented compared well with that directly measured in the course of the CHABLIS experiments. The model systematically overestimated OH and HO2 levels, likely a consequence of the combined effects of (a) estimated physical parameters and (b) uncertainties within the halogen, particularly iodine, chemical scheme. The principal sources of HOx radicals were the photolysis and bromine-initiated oxidation of HCHO, together with O(1D)+H2O. The main sinks for HOx were peroxy radical self- and cross-reactions, with the sum of all halogen-mediated HOx loss processes accounting for 40% of the total sink. Reactions with the halogen monoxides dominated CH3O2–HO2–OH interconversion, with associated local chemical ozone destruction in place of the ozone production which is associated with radical cycling driven by the analogous NO reactions. The analysis highlights the need for observations of physical parameters such as aerosol surface area and boundary layer structure to constrain such calculations, and the dependence of simulated radical levels and ozone loss rates upon a number of uncertain kinetic and photochemical parameters for iodine species.

Download Full-text