scholarly journals Summertime photochemistry during CAREBeijing-2007: RO<sub> x</sub> budgets and O<sub>3</sub> formation

2012 ◽  
Vol 12 (2) ◽  
pp. 4679-4717 ◽  
Author(s):  
Z. Liu ◽  
Y. Wang ◽  
D. Gu ◽  
C. Zhao ◽  
L. G. Huey ◽  
...  
Keyword(s):  
Transport Model ◽  
Control Strategies ◽  
Eastern China ◽  
Heterogeneous Reactions ◽  
Transition Regime ◽  
Oxygenated Volatile Organic Compounds ◽  
In Situ Observations ◽  
Reactive Uptake Coefficient ◽  
Beijing China

Abstract. We analyze summertime photochemistry near the surface over Beijing, China, using a 1-D photochemical model (Regional chEmical and trAnsport Model, REAM-1D) constrained by in situ observations, focusing on the budgets of ROx (OH + HO2 + RO2) radicals and O3 formation. The daytime average of total ROx primary production rate in Beijing is ~6.6 ppbv h−1, among the highest found in urban atmospheres. The largest primary ROx source in Beijing is photolysis of oxygenated volatile organic compounds (OVOCs), which produces HO2 and RO2 at average daytime rates of 2.5 ppbv h−1 and 1.7 ppbv h−1, respectively. Photolysis of excess HONO from the unknown heterogeneous source is a predominant primary OH source at 2.2 ppbv h−1, much larger than that of O1D + H2O (0.4 ppbv h−1). The largest ROx sink is via OH + NO2 reaction (1.6 ppbv h−1), followed by formation of RO2NO2 (1.0 ppbv h−1) and RONO2 (0.7 ppbv h−1). Due to the large aerosol surface area, aerosol uptake of HO2 appears to be another important radical sink, although the estimate of its magnitude is highly variable depending on the reactive uptake coefficient value used. The daytime average O3 production and loss rates are 32 ppbv h−1 and 6.2 ppbv h−1, respectively. Assuming NO2 to be the source of excess HONO, the NO2 to HONO transformation leads to significant O3 loss and reduction of its lifetime. Our observation-based modeling analyses suggest that VOCs and heterogeneous reactions (e.g. HONO formation and aerosol uptake HO2) play major roles in the primary radical budget and O3 formation in Beijing. Among the VOC precursors for OVOCs, which strongly affect ROx budgets and O3 formation, aromatics are the largest contributor. One important ramification is that O3 production is neither NOx nor VOC limited, but in a transition regime, where reduction of either NOx or VOCs could result in reduction of O3 production. The transition regime implies more flexibility in the O3 control strategies than a binary system of either NOx or VOC limited regime. Further research on the spatial extent of the transition regime over the polluted eastern China is critically important for controlling regional O3 pollution.

scholarly journals Summertime photochemistry during CAREBeijing-2007: RO<sub>x</sub> budgets and O<sub>3</sub> formation

2012 ◽  
Vol 12 (16) ◽  
pp. 7737-7752 ◽  
Author(s):  
Z. Liu ◽  
Y. Wang ◽  
D. Gu ◽  
C. Zhao ◽  
L. G. Huey ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Planetary Boundary Layer ◽  
Transport Model ◽  
Control Strategies ◽  
Eastern China ◽  
Heterogeneous Reactions ◽  
Transition Regime ◽  
Near Surface ◽  
Modeling Analysis ◽  
Beijing China

Abstract. We analyze summertime photochemistry near the surface in Beijing, China, using a 1-D photochemical model (Regional chEmical and trAnsport Model, REAM-1D) constrained by in situ observations, focusing on the budgets of ROx (OH + HO2 + RO2) radicals and O3 formation. While the modeling analysis focuses on near-surface photochemical budgets, the implications for the budget of O3 in the planetary boundary layer are also discussed. In terms of daytime average, the total ROx primary production rate near the surface in Beijing is 6.6 ppbv per hour (ppbv h−1, among the highest found in urban atmospheres. The largest primary ROx source in Beijing is photolysis of oxygenated volatile organic compounds (OVOCs), which produces HO2 and RO2 at 2.5 ppbv h−1 and 1.7 ppbv h−1, respectively. Photolysis of excess HONO from an unknown heterogeneous source is the predominant primary OH source at 2.2 ppbv h−1, much larger than that of O1D+H2O (0.4 ppbv h−1). The largest ROx sink is via OH + NO2 reaction (1.6 ppbv h−1), followed by formation of RO2NO2 (1.0 ppbv h−1) and RONO2 (0.7 ppbv h−1). Due to the large aerosol surface area, aerosol uptake of HO2 appears to be another important radical sink, although the estimate of its magnitude is highly variable depending on the uptake coefficient value used. The daytime average O3 production and loss rates near the surface are 32 ppbv h−1 and 6.2 ppbv h−1, respectively. Assuming NO2 to be the source of excess HONO, the NO2 to HONO transformation leads to considerable O3 loss and reduction of its lifetime. Our observation-constrained modeling analysis suggests that oxidation of VOCs (especially aromatics) and heterogeneous reactions (e.g. HONO formation and aerosol uptake HO2) play potentially critical roles in the primary radical budget and O3 formation in Beijing. One important ramification is that O3 production is neither NOx nor VOC limited, but in a transition regime where reduction of either NOx or VOCs could result in reduction of O3 production. The transition regime implies more flexibility in the O3 control strategies than a binary system of either NOx or VOC limited regime. The co-benefit of concurrent reduction of both NOx and VOCs in reducing column O3 production integrated in the planetary boundary layer is significant. Further research on the spatial extent of the transition regime over the polluted eastern China is critically important for controlling regional O3 pollution.

scholarly journals A comparison of atmospheric CO<sub>2</sub> flux signals obtained from GEOS-Chem flux inversions constrained by in situ or GOSAT observations

2018 ◽  
Author(s):  
Saroja M. Polavarapu ◽  
Feng Deng ◽  
Brendan Byrne ◽  
Dylan B. A. Jones ◽  
Micheal Neish
Keyword(s):  
Transport Model ◽  
Atmospheric Transport ◽  
Co2 Flux ◽  
Boreal Summer ◽  
Spatial Structures ◽  
Independent Observations ◽  
In Situ Observations ◽  
The Difference ◽  
Observing Systems

Abstract. The CO2 flux signal is defined as the difference of the four-dimensional CO2 field obtained by integrating an atmospheric transport model with posterior fluxes and that obtained with prior fluxes. It is a function of both the model and the prior fluxes and it can provide insight into how posterior fluxes inform CO2 distributions. Here, we use the GEOS-Chem transport model constrained by either GOSAT or in situ observations to obtain two sets of posterior flux estimates in order to compare the flux signals obtained from the two different observing systems. Flux signals are also computed using two different models. The global flux signal in the troposphere primarily reflects the northern extratropics whereas the global flux signal in the stratosphere mainly reflects tropical contributions. While both observing systems constrain the global budget for 2010 equally well, stronger seasonal variations of the flux signal are obtained with GOSAT. Posterior CO2 distributions obtained with in situ observations better agree with TCCON measurements over an 18-month time period, but GOSAT-informed posterior fluxes better constrain the seasonal cycle at northern extratropical sites. Zonal standard deviations of the flux signal exceed the minimal value (defined by uncertainty in meteorological analyses) through most of the year when GOSAT observations are used, but when in situ observations are used, the minimum value is exceeded only in boreal summer. This indicates a potential for flux estimates constrained by GOSAT data to retrieve spatial structures within a zonal band throughout the year in the tropics and through most of the year in the northern extratropics. Verification of such spatial structures will require a dense network of independent observations.

scholarly journals Estimation of volatile organic compound emissions for Europe using data assimilation

2013 ◽  
Vol 13 (12) ◽  
pp. 5887-5905 ◽  
Author(s):  
M. R. Koohkan ◽  
M. Bocquet ◽  
Y. Roustan ◽  
Y. Kim ◽  
C. Seigneur
Keyword(s):  
Maximum Likelihood ◽  
Western Europe ◽  
Transport Model ◽  
Monitoring Network ◽  
Monitoring And Evaluation ◽  
Chemical Transport Model ◽  
Volatile Organic ◽  
In Situ Observations ◽  
Non Gaussian

Abstract. The emissions of non-methane volatile organic compounds (VOCs) over western Europe for the year 2005 are estimated via inverse modelling by assimilation of in situ observations of concentration and then subsequently compared to a standard emission inventory. The study focuses on 15 VOC species: five aromatics, six alkanes, two alkenes, one alkyne and one biogenic diene. The inversion relies on a validated fast adjoint of the chemical transport model used to simulate the fate and transport of these VOCs. The assimilated ground-based measurements over Europe are provided by the European Monitoring and Evaluation Programme (EMEP) network. The background emission errors and the prior observational errors are estimated by maximum-likelihood approaches. The positivity assumption on the VOC emission fluxes is pivotal for a successful inversion, and this maximum-likelihood approach consistently accounts for the positivity of the fluxes. For most species, the retrieved emissions lead to a significant reduction of the bias, which underlines the misfit between the standard inventories and the observed concentrations. The results are validated through a forecast test and a cross-validation test. An estimation of the posterior uncertainty is also provided. It is shown that the statistically consistent non-Gaussian approach based on a reliable estimation of the errors offers the best performance. The efficiency in correcting the inventory depends on the lifetime of the VOCs and the accuracy of the boundary conditions. In particular, it is shown that the use of in situ observations using a sparse monitoring network to estimate emissions of isoprene is inadequate because its short chemical lifetime significantly limits the spatial radius of influence of the monitoring data. For species with a longer lifetime (a few days), successful, albeit partial, emission corrections can reach regions hundreds of kilometres away from the stations. Domain-wide corrections of the emission inventories of some VOCs are significant, with underestimations of the order of a factor of 2 for propane, ethane, ethylene and acetylene.

scholarly journals Emission and transport of bromocarbons: from the West Pacific ocean into the stratosphere

2012 ◽  
Vol 12 (22) ◽  
pp. 10633-10648 ◽  
Author(s):  
S. Tegtmeier ◽  
K. Krüger ◽  
B. Quack ◽  
E. L. Atlas ◽  
I. Pisso ◽  
...  
Keyword(s):  
Ozone Depletion ◽  
Transport Model ◽  
Source Region ◽  
Convective Transport ◽  
Tropical Atlantic ◽  
The West ◽  
West Pacific ◽  
Oceanic Emissions ◽  
In Situ Observations

Abstract. Oceanic emissions of halogenated very short-lived substances (VSLS) are expected to contribute significantly to the stratospheric halogen loading and therefore to ozone depletion. The amount of VSLS transported into the stratosphere is estimated based on in-situ observations around the tropical tropopause layer (TTL) and on modeling studies which mostly use prescribed global emission scenarios to reproduce observed atmospheric concentrations. In addition to upper-air VSLS measurements, direct observations of oceanic VSLS emissions are available along ship cruise tracks. Here we use such in-situ observations of VSLS emissions from the West Pacific and tropical Atlantic together with an atmospheric Lagrangian transport model to estimate the direct contribution of bromoform (CHBr3), and dibromomethane (CH2Br2) to the stratospheric bromine loading as well as their ozone depletion potential. Our emission-based estimates of VSLS profiles are compared to upper-air observations and thus link observed oceanic emissions and in situ TTL measurements. This comparison determines how VSLS emissions and transport in the cruise track regions contribute to global upper-air VSLS estimates. The West Pacific emission-based profiles and the global upper-air observations of CHBr3 show a relatively good agreement indicating that emissions from the West Pacific provide an average contribution to the global CHBr3 budget. The tropical Atlantic, although also being a CHBr3 source region, is of less importance for global upper-air CHBr3 estimates as revealed by the small emission-based abundances in the TTL. Western Pacific CH2Br2 emission-based estimates are considerably smaller than upper-air observations as a result of the relatively low sea-to-air flux found in the West Pacific. Together, CHBr3 and CH2Br2 emissions from the West Pacific are projected to contribute to the stratospheric bromine budget with 0.4 pptv Br on average and 2.3 pptv Br for cases of maximum emissions through product and source gas injection. These relatively low estimates reveal that the tropical West Pacific, although characterized by strong convective transport, might overall contribute less VSLS to the stratospheric bromine budget than other regions as a result of only low CH2Br2 and moderate CHBr3 oceanic emissions.

scholarly journals Remote sensed and in situ constraints on processes affecting tropical tropospheric ozone

2006 ◽  
Vol 6 (6) ◽  
pp. 11465-11520 ◽  
Author(s):  
B. Sauvage ◽  
R. V. Martin ◽  
A. van Donkelaar ◽  
X. Liu ◽  
K. Chance ◽  
...  
Keyword(s):  
Biomass Burning ◽  
Tropospheric Ozone ◽  
Transport Model ◽  
Lower Troposphere ◽  
In Situ Measurements ◽  
Top Down ◽  
Upper Troposphere ◽  
In Situ Observations ◽  
Tropospheric O3

Abstract. We use a global chemical transport model (GEOS-Chem) to evaluate the consistency of satellite measurements of lightning flashes and ozone precursors with in situ measurements of tropical tropospheric ozone. The measurements are tropospheric O3, NO2, and HCHO columns from the GOME satellite instrument, lightning flashes from the OTD and LIS instruments, profiles of O3, CO, and relative humidity from the MOZAIC aircraft program, and profiles of O3 from the SHADOZ ozonesonde network. We interpret these multiple data sources with our model to better understand what controls tropical tropospheric ozone. Tropical tropospheric ozone is mainly affected by lightning and convection in the upper troposphere and by surface emissions in the lower troposphere. Scaling the spatial distribution of lightning in the model to the observed flash counts improves the simulation of O3 in the upper troposphere by 5–20 ppbv versus in situ observations and by 1–4 Dobson Units versus GOME retrievals of tropospheric O3 columns. A lightning source strength of 5±2 Tg N/yr best represents in situ observations from aircraft and ozonesonde. Tropospheric NO2 and HCHO columns from GOME are applied to provide top-down constraints on emission inventories of NOx (biomass burning and soils) and VOCs (biomass burning). The top-down biomass burning inventory is larger by a factor of 2 for HCHO and alkenes, and by 2.6 for NOx over northern equatorial Africa. These emissions increase lower tropospheric O3 by 5–20 ppbv, improving the simulation versus aircraft observations, and by 4 Dobson Units versus GOME observations of tropospheric O3 columns. Emission factors in the a posteriori inventory are more consistent with a recent compilation from in situ measurements. The ozone simulation using two different dynamical schemes (GEOS-3 and GEOS-4) is evaluated versus observations; GEOS-4 better represents O3 observations by 5–15 ppbv due to enhanced convective detrainment in the upper troposphere. Heterogeneous uptake of HNO3 on aerosols reduces simulated O3 by 5–7 ppbv, reducing a model bias versus in situ observations over and downwind of deserts. Exclusion of HO2 uptake on aerosols improves O3 by 5 ppbv in biomass burning regions.

scholarly journals Validation of satellite formaldehyde (HCHO) retrievals using observations from 12 aircraft campaigns

2020 ◽  
Author(s):  
Lei Zhu ◽  
Gonzalo González Abad ◽  
Caroline R. Nowlan ◽  
Christopher Chan Miller ◽  
Kelly Chance ◽  
...  
Keyword(s):  
Transport Model ◽  
A Priori ◽  
Chemical Transport Model ◽  
Shape Factors ◽  
Atmospheric Lifetime ◽  
Volatile Organic ◽  
Satellite Sensors ◽  
Systematic Biases ◽  
In Situ Observations

Abstract. Formaldehyde (HCHO) has been measured from space for more than two decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and acronyms), providing constraints on underlying emissions and chemistry. However, satellite HCHO products from different satellite sensors using different algorithms have received little validation so far. The accuracy and consistency of HCHO retrievals remain largely unclear. Here we develop a global validation platform for satellite HCHO retrievals using in situ observations from 12 aircraft campaigns with a chemical transport model (GEOS-Chem) as the intercomparison method. Application to the NASA operational OMI HCHO product indicates slight biases (−30.9 % to +16.0 %) under high-HCHO conditions partially caused by a priori shape factors used in the retrievals, while high biases (+113.9 % to +194.6 %) under low-HCHO conditions due mainly to slant column fitting and radiance reference sector correction. By providing quick assessment to systematic biases in satellite products over large domains, the platform facilitates, in an iterative process, optimization of retrieval settings and the minimization of retrieval biases. It is also complementary to localized validation efforts based on ground observations and aircraft spirals.

Evaluation of multiple soil moisture products using in-situ observations over China

2021 ◽  
Author(s):  
Huiqing Li ◽  
Aizhong Ye ◽  
Yuhang Zhang ◽  
Wenwu Zhao
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Yellow River ◽  
Eastern China ◽  
Land Surface Model ◽  
Spatial And Temporal Variation ◽  
Surface Model ◽  
Drought Assessment ◽  
In Situ Observations

&lt;p&gt;Soil moisture (SM), a vital variable in the climate system, is applied in many fields. But the existing SM data sets from different sources have great uncertainty, hence need comprehensive verification. In this study, we collected and evaluated ten latest commonly used SM products over China, including four reanalysis data (ERA-Interim, ERA5, NCEP R2 and CFSR/CFSV2), three land surface model products (GLDAS 2.1 Noah, CLSM and VIC) and three remote sensing products (ESA CCI ACTIVE, COMBINED and PASSIVE). These products in their overlap period (2000-2018) were inter-compared in spatial and temporal variation. In addition, their accuracy was verified by a large quantity of in-situ observations. The results show that the ten SM products have roughly similar spatial patterns and small inter-annual differences, but there are still some deviations varying in regions and products. ERA5 displays the most encouraging overall performance in China. The estimates of SM in the northwest of China among all products generally perform poorly on capturing in-situ SM variability due to less coverage of observations. CLSM and ERA5 have a satisfactory correlation coefficient with the observed SM (R&gt;0.7) in the northeast and south of China, respectively. ESA CCI ACTIVE performs with the optimal mean Equitable Threat Score (ETS) value, which indicates the promising ability to drought assessment, followed by CFSR/CFSV2 and ERA5. Specifically, ESA CCI ACTIVE expresses higher ETS in the Yellow River Basin, while CFSR/CFSV2 and ERA5 are more applicable in most areas of the eastern China. This study provides a reasonable reference for the application of SM products in China.&lt;/p&gt;

scholarly journals A dedicated flask sampling strategy developed for ICOS stations based on CO<sub>2</sub> and CO measurements and STILT footprint modelling

2020 ◽  
Author(s):  
Ingeborg Levin ◽  
Ute Karstens ◽  
Markus Eritt ◽  
Fabian Maier ◽  
Sabrina Arnold ◽  
...  
Keyword(s):  
Quality Control ◽  
Fossil Fuel ◽  
Transport Model ◽  
Sampling Strategy ◽  
Observation System ◽  
Air Samples ◽  
Footprint Model ◽  
In Situ Observations ◽  
Existing Data

Abstract. In situ CO2 and CO measurements from five atmospheric ICOS (Integrated Carbon Observation System) stations have been analysed together with footprint model runs from the regional transport model STILT, to develop a dedicated strategy for flask sampling with an automated sampler. Flask sampling in ICOS has three different purposes: (1) Provide an independent quality control for in situ observations, (2) provide representative information on atmospheric components currently not monitored in situ at the stations, (3) collect samples for 14CO2 analysis that are significantly influenced by fossil fuel CO2 (ffCO2) emission areas. Based on the existing data and experimental results obtained at the Heidelberg pilot station with a prototype flask sampler, we suggest that single flask samples should be collected regularly every third day around noon/afternoon from the highest level of a tower station. Air samples shall be collected over one hour with equal temporal weighting to obtain a true hourly mean. At all stations studied, more than 50 % of flasks to be collected around mid-day will likely be sampled during low ambient variability (

scholarly journals Validation of satellite formaldehyde (HCHO) retrievals using observations from 12 aircraft campaigns

2020 ◽  
Vol 20 (20) ◽  
pp. 12329-12345 ◽  
Author(s):  
Lei Zhu ◽  
Gonzalo González Abad ◽  
Caroline R. Nowlan ◽  
Christopher Chan Miller ◽  
Kelly Chance ◽  
...  
Keyword(s):  
Transport Model ◽  
A Priori ◽  
Chemical Transport Model ◽  
Atmospheric Lifetime ◽  
Volatile Organic ◽  
Main Driver ◽  
Satellite Sensors ◽  
Systematic Biases ◽  
In Situ Observations

Abstract. Formaldehyde (HCHO) has been measured from space for more than 2 decades. Owing to its short atmospheric lifetime, satellite HCHO data are used widely as a proxy of volatile organic compounds (VOCs; please refer to Appendix A for abbreviations and acronyms), providing constraints on underlying emissions and chemistry. However, satellite HCHO products from different satellite sensors using different algorithms have received little validation so far. The accuracy and consistency of HCHO retrievals remain largely unclear. Here we develop a validation platform for satellite HCHO retrievals using in situ observations from 12 aircraft campaigns with a chemical transport model (GEOS-Chem) as the intercomparison method. Application to the NASA operational OMI HCHO product indicates negative biases (−44.5 % to −21.7 %) under high-HCHO conditions, while it indicates high biases (+66.1 % to +112.1 %) under low-HCHO conditions. Under both conditions, HCHO a priori vertical profiles are likely not the main driver of the biases. By providing quick assessment of systematic biases in satellite products over large domains, the platform facilitates, in an iterative process, optimization of retrieval settings and the minimization of retrieval biases. It is also complementary to localized validation efforts based on ground observations and aircraft spirals.

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