Model For Ozone And Related Chemical Tracers, Version 4 Research Articles

Detection of outflow of formaldehyde and glyoxal from the African continent to the Atlantic Ocean with a MAX-DOAS instrument

Abstract. Trace gas maps retrieved from satellite measurements show enhanced levels of the atmospheric volatile organic compounds formaldehyde (HCHO) and glyoxal (CHOCHO) over the Atlantic Ocean. To validate the spatial distribution of this continental outflow, ship-based measurements were taken during the Continental Outflow of Pollutants towards the MArine tRoposphere (COPMAR) project. A Multi-AXis Differential Optical Absorption Spectrometer (MAX-DOAS) was operated aboard the research vessel (RV) Maria S. Merian during cruise MSM58/2. This cruise was conducted in October 2016 from Ponta Delgada (Azores) to Cape Town (South Africa), crossing between Cabo Verde and the African continent. The instrument was continuously scanning the horizon, looking towards the African continent. Enhanced levels of HCHO and CHOCHO were found in the area of expected outflow during this cruise. The observed spatial gradients of HCHO and CHOCHO along the cruise track agree with the spatial distributions from satellite measurements and the Model for OZone and Related chemical Tracers version 4 (MOZART-4) model simulations. The continental outflow from the African continent is observed in an elevated layer, higher than 1000 m, and probably originates from biogenic emissions or biomass burning according to FLEXible PARTicle dispersion model (FLEXPART) emission sensitivities.

Impact of chemical initial and lateral boundary conditions on air quality prediction

Accurate representation of initial and boundary conditions of chemical species in numerical models is a major challenge for air quality prediction. Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) is an offline global chemical transport model simulating various gases and particulates in the atmosphere. In this work, MOZART-4 analysis is used to modify the chemical boundary conditions over India to improve the forecast in an online-coupled model. A sensitivity study has been performed using the Weather Research and Forecasting (WRF) model coupled with Chemistry model (WRF-Chem) for the highly polluted winter month of December 2016. Daily two parallel experiments are performed from the WRF-Chem model with and without updating chemical initial and lateral boundary conditions using MOZART-4 analyses. Results show that the tropospheric ozone (O3) and surface carbon monoxide (CO) forecasts are improved by 6% and 20%, respectively when MOZART-4 analysis is used to update chemical initial and lateral boundary conditions. Moreover, prediction of O3 and CO is also improved vertically (reduction in root mean square difference by 58% and 26%, respectively) in different forecast lengths. The percentage improvement in surface CO, particulate matter of size less than 2.5 μm (PM2.5) and particulate matter of size less than 10 μm (PM10) forecasts is ∼22%, ∼4.3% and ∼20%, respectively when compared against ground observations from Central Pollution Control Board (CPCB), New Delhi stations. Overall, we observed improvement in O3, CO, PM2.5 and PM10 forecast using WRF-Chem model after initialization of chemical conditions from MOZART-4 analysis.

The influence of local meteorology and convection on carbon monoxide distribution over Chennai

The influence of local meteorology and convection activities on the vertical distribution of carbon monoxide (CO) over Chennai in southern India was investigated by analysing the measurements of ozone aboard airbus in-service aircraft observations during the years 2012–2013. The seasonal variation of CO in the free troposphere was observed to be different and less pronounced than that in the planetary boundary layer (PBL). The near surface mixing ratio of CO was the highest (\(190 \pm 68\,\hbox {ppbv}\)) during winter, while enhanced values (\(117 \pm 11\,\hbox {ppbv}\)) in the free troposphere were observed during post-monsoon. The mixing ratios were the lowest throughout the troposphere during the monsoon. In the PBL, the mixing ratios of CO showed a decline with an increase in wind speed and were the highest (\({>}200\,\hbox {ppbv}\)) under stagnant conditions (\(1{-}2\,\hbox {m s}^{-1})\) during winter. The higher CO in the lower free troposphere during the pre-monsoon period is attributed to the stronger biomass burning emissions. In the middle–upper troposphere, higher levels of CO during post-monsoon are due to the enhanced vertical mixing of regional emissions associated with weaker wind shears and frequent convection activities. Overall, the contrasting effects of stronger CO emissions can be observed in winter/pre-monsoon, while the efficient vertical mixing during the monsoon/post-monsoon season governs the observed seasonality of CO. The model for ozone and related chemical tracers, version 4 (MOZART-4) provides a reasonable representation of the convection effect on the CO mixing ratio. This study highlights a need to conduct more observations, especially of aircraft-borne instruments, to understand the effects of regional-scale emissions and dynamics in the middle–upper tropospheric chemistry over South Asia.

Source attribution of carbon monoxide and ozone over the Indian subcontinent using MOZART-4 chemistry transport model

Daily simulations of tropospheric carbon monoxide (CO) and ozone (O3) have been made using MOZART-4 (Model for OZone And Related chemical Tracers version 4) during 2007–08. The model simulated CO and O3 are evaluated against MOZAIC (Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft) airborne observations over Hyderabad and IASI (Infrared Atmospheric Sounding Interferometer) retrievals over five most populous cities of India i.e. Mumbai, Delhi, Bangalore, Hyderabad, and Ahmedabad. The MOZAIC tropospheric column showed winter maxima and summer minima for CO whereas spring maxima and summer minima for O3. These seasonal features are reproduced well by model over Hyderabad. Model lower and middle tropospheric CO (O3) columns are positively biased by about 14 (8) ppbv as compared to MOZAIC observations. Model underestimated (overestimated) IASI CO columns during pre-monsoon (post-monsoon) while it overestimated IASI O3 columns throughout the year. Model simulated column of CO and O3 are positively biased by 4–13% and 23–33% respectively as compared to the IASI retrievals over five most populous cities. Tagged and sensitivity simulations of MOZART-4 have been used to quantify the contribution of different sources to the tropospheric CO and O3 distribution over the Indian landmass region. At surface, anthropogenic contribution varies from 55% to 81% during different seasons with an annual average contribution of 67%. This contribution decreases with increasing altitude up to 35% at 300 hPa. The contribution of photochemically produced CO is found to be 9–33% at surface. Unlike ANT-CO, the photochemically produced CO increases with altitude as it reaches up to 48% at 300 hPa. Surface BB-CO contributes upto 30% over parts of North East India during pre-monsoon season. Contribution of NAT-CO is found to be negligible (Approximately 6%) near surface as well as at the higher altitudes. Sensitivity simulations are used to decompose the total ozone (TO) into contributions from enhancement of ozone from Indian anthropogenic emissions, referred as Indian pollution ozone (IPO) and from the total background ozone (TBO). Annual total ozone is found to be 30 to 70 ppbv at surface and 77 to 85 ppbv at 300 hPa over the Indian landmass region. IPO and TBO contribute annually 58% and 42% at surface while 45% and 55% at 300 hPa respectively. The IPO contributes strongly at surface, with maximum (68%) impact during pre-monsoon season.

SEASONAL AND SPATIAL VARIABILITY OF OZONE INFERRED FROM GLOBAL CHEMISTRY TRANSPORT MODEL SIMULATIONS OVER INDIA

Abstract. In the present study, 3-D chemical transport model, MOZART-4 (Model for Ozone and Related chemical Tracers-Version-4) has been used to study the seasonal and spatial distribution of surface ozone (O3) over India. To illustrate the capabilities of model, the simulations are compared with the ground-based observations. The model reproduces the principal features present in ground-based observations. However, model is unable to simulate very low concentration of O3 during monsoon months. The model simulations are used to quantify the contribution of background ozone and Indian anthropogenic emissions to the variability of surface O3. The spatial distribution of total O3 (TO) shows maximum over Indo-Gangetic plains (IGP) and Eastern India while minimum over southern Indian region. The seasonal cycle of TO vary from 34.2 ± 7.6 to 51.9 ± 4.9 ppbv over the Indian landmass region due to changes in its topography and ozone lifetime. Annual mean total background O3 (TBO) over India shows highest during spring (29.3 ± 5.0 ppbv) and lowest during monsoon (19.6 ± 3.4 ppbv). Both Natural background O3 (NBO) and pollution background O3 (PBO) shows a minimum in summer which are essentially following the seasonal changes of total ozone. Significant variation of India pollution O3 (IPO) is found over India and the spatial variation of IPO follows the spatial variation of TO as well as spatial variation of emission of ozone precursors.

Evaluating simplified chemical mechanisms within present-day simulations of the Community Earth System Model version 1.2 with CAM4 (CESM1.2 CAM-chem): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast chemistry

Abstract. While state-of-the-art complex chemical mechanisms expand our understanding of atmospheric chemistry, their sheer size and computational requirements often limit simulations to short lengths or ensembles to only a few members. Here we present and compare three 25-year present-day offline simulations with chemical mechanisms of different levels of complexity using the Community Earth System Model (CESM) Version 1.2 CAM-chem (CAM4): the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) mechanism, the Reduced Hydrocarbon mechanism, and the Super-Fast mechanism. We show that, for most regions and time periods, differences in simulated ozone chemistry between these three mechanisms are smaller than the model–observation differences themselves. The MOZART-4 mechanism and the Reduced Hydrocarbon are in close agreement in their representation of ozone throughout the troposphere during all time periods (annual, seasonal, and diurnal). While the Super-Fast mechanism tends to have higher simulated ozone variability and differs from the MOZART-4 mechanism over regions of high biogenic emissions, it is surprisingly capable of simulating ozone adequately given its simplicity. We explore the trade-offs between chemical mechanism complexity and computational cost by identifying regions where the simpler mechanisms are comparable to the MOZART-4 mechanism and regions where they are not. The Super-Fast mechanism is 3 times as fast as the MOZART-4 mechanism, which allows for longer simulations or ensembles with more members that may not be feasible with the MOZART-4 mechanism given limited computational resources.

Impact of time-dependent chemical boundary conditions on tropospheric ozone simulation with WRF-Chem: An experiment over the Metropolitan Area of São Paulo

WRF-Chem (Weather Research and Forecasting with Chemistry Model) is being used to perform air quality forecast over the southeast Brazil with a domain centered in the Metropolitan Area of São Paulo (MASP). The simulations are used to understand the pollutants behavior concerning the fluxes to and from the urban areas, to examine the formation of secondary pollutants (e.g., tropospheric ozone), and to validate the efficacy of air quality policies implementation, particularly the ones that are related to the vehicular fuel used in the region. One important factor to improve the air quality simulations is the configuration of suited inflow boundary conditions for the chemical species. In that context, the objective of this study is to assess the impacts of using time-dependent Chemical Lateral Boundary Conditions (CBC) on tropospheric ozone simulations with WRF-Chem. Two simulations were carried out using Carbon-Bond Mechanism version Z (CBMZ). The first simulation was a set-up to run with WRF-Chem default CBC, and the second one using time-dependent CBC obtained from MOZART-4 (Model for Ozone and Related chemical Tracers, version 4) simulations. The period of study was from May 15 to May 18 and from October 30 to November 1, 2006, when a comprehensive experiment with ozonesondes launching and surface measurements was performed. Results show that using MOZART-4 CBC reduced mean bias, RMSE and slightly improved correlation coefficients for ground level ozone as well as ozone vertical profile above 3 km. These improvements were more significant during periods with lower photochemical activity. However, underestimation of ozone concentration peaks was also observed in this period, which can be an issue for operational air quality forecasting.

Temporal characteristics of atmospheric ammonia and nitrogen dioxide over China based on emission data, satellite observations and atmospheric transport modeling since 1980

Abstract. China is experiencing intense air pollution caused in large part by anthropogenic emissions of reactive nitrogen (Nr). Atmospheric ammonia (NH3) and nitrogen dioxide (NO2) are the most important precursors for Nr compounds (including N2O5, HNO3, HONO and particulate NO3− and NH4+) in the atmosphere. Understanding the changes in NH3 and NO2 has important implications for the regulation of anthropogenic Nr emissions and is a requirement for assessing the consequence of environmental impacts. We conducted the temporal trend analysis of atmospheric NH3 and NO2 on a national scale since 1980 based on emission data (during 1980–2010), satellite observation (for NH3 since 2008 and for NO2 since 2005) and atmospheric chemistry transport modeling (during 2008–2015).Based on the emission data, during 1980–2010, significant continuous increasing trends in both NH3 and NOx were observed in REAS (Regional Emission inventory in Asia, for NH3 0.17 and for NOx 0.16 kg N ha−1 yr−2) and EDGAR (Emissions Database for Global Atmospheric Research, for NH3 0.24 and for NOx 0.17 kg N ha−1 yr−2) over China. Based on the satellite data and atmospheric chemistry transport model (CTM) MOZART-4 (Model for Ozone and Related chemical Tracers, version 4), the NO2 columns over China increased significantly from 2005 to 2011 and then decreased significantly from 2011 to 2015; the satellite-retrieved NH3 columns from 2008 to 2014 increased at a rate of 2.37 % yr−1. The decrease in NO2 columns since 2011 may result from more stringent strategies taken to control NOx emissions during the 12th Five Year Plan, while no control policy has focused on NH3 emissions. Our findings provided an overall insight into the temporal trends of both NO2 and NH3 since 1980 based on emission data, satellite observations and atmospheric transport modeling. These findings can provide a scientific background for policy makers that are attempting to control atmospheric pollution in China. Moreover, the multiple datasets used in this study have implications for estimating long-term Nr deposition datasets to assess its impact on soil, forest, water and greenhouse balance.

Validation of lower tropospheric carbon monoxide inferred from MOZART model simulation over India

In the present study, MOZART-4 (Model for Ozone and Related chemical Tracers-Version-4) simulation has been made from 2003 to 2007 and compared with satellite and in-situ observations with a specific focus on Indian subcontinent to illustrate the capabilities of MOZART-4 model. The model simulated CO have been compared with latest version (version-6) of MOPITT (Measurement Of Pollution In The Troposphere) carbon monoxide (CO) retrievals at 900, 800 and 700hPa. Model reproduces major features present in satellite observations. However model significantly overestimates CO over the entire Indian region at 900hPa and moderately overestimates at 800hPa and 700hPa. The frequency distribution of all simulated data points with respect to MOZART error shows maximum in the error range of 10–20% at all pressure levels. Over total Indian landmass, the percentage of gridded CO data that are being overestimated in the range of 0–30% at 900hPa, 800hPa and 700hPa are 58%, 62% and 66% respectively. The study reflects very good correlation between two datasets over Central India (CI) and Southern India (SI). The coefficient of determination (r2) is found to be 0.68–0.78 and 0.70–0.78 over the CI and SI respectively. The weak correlation is evident over Northern India (NI) with r2 values of 0.1–0.3. Over Eastern India (EI), Good correlation at 800hPa (r2=0.72) and 700hPa (r2=0.66) whereas moderately weak correlation at 900hPa (r2=0.48) has been observed. In contrast, Over Western India (WI), strong correlation is evident at 900hPa (r2=0.64) and moderately weak association is found to be present at 800hPa and 700hPa. Model fairly reproduces seasonal cycle of CO in the lower troposphere over most of the Indian regions. However, during June to December, model shows overestimation over NI. The magnitude of overestimation is increasing linearly from 900hPa to 700hPa level. During April–June months, model results are coinciding with observed CO concentrations over SI region at 900hPa. Model simulation has been compared with surface in-situ observations over ten Indian locations. Model performance is found to be moderate to good over various observational locations. However, over highly polluted megacities, model underestimates observed CO concentration by up to 3500ppbv. A case study over the forest fire prone area reveals the clear increase of modeled and retrieved CO in February–March and a decrease in May which is coinciding with biomass burning emissions and fire counts. Model performance is found to be relatively poor over this region with r2 of 0.29 and slope of 0.56.

Spatiotemporal Distribution and Source Attribution of SOA in China

Secondary organic aerosol (SOA) is an important pollutant due to its significant impact on atmospheric pollution, climate change and human health. Understanding the source and distribution of SOA is the prerequisite of air pollution control. This study utilized the global chemical transport model MOZART4 (Model for Ozone and Related Chemical Tracers, Version 4) coupled with the parameterizations of SOA multiphase formation, to simulate the spatial and temporal distribution of SOA in China, and analyzed the source contributions of SOA from the aspects of different precursors and regions. Our results indicate that the majority of SOA production happened over the east and the south China due to the availability of SOA precursors, with the summertime production a factor of 2.5 higher than that in winter. Anthropogenic emissions played a dominant role in SOA production, accounting for 55% of SOA source in China, with the rest from biogenic sources (45%). The domestic emissions contributed 77% of SOA production in China, mainly influencing the SOA concentration distribution near the surface of eastern China, especially over North China Plain. Foreign emissions mainly dominated the SOA abundance in western China, especially at higher altitudes mainly due to the rare domestic emission over these areas and the long-range transportation of SOA.

The Impact of Individual Anthropogenic Emissions Sectors on the Global Burden of Human Mortality due to Ambient Air Pollution.

Background:Exposure to ozone and fine particulate matter (PM2.5) can cause adverse health effects, including premature mortality due to cardiopulmonary diseases and lung cancer. Recent studies quantify global air pollution mortality but not the contribution of different emissions sectors, or they focus on a specific sector.Objectives:We estimated the global mortality burden of anthropogenic ozone and PM2.5, and the impact of five emissions sectors, using a global chemical transport model at a finer horizontal resolution (0.67° × 0.5°) than previous studies.Methods:We performed simulations for 2005 using the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4), zeroing out all anthropogenic emissions and emissions from specific sectors (All Transportation, Land Transportation, Energy, Industry, and Residential and Commercial). We estimated premature mortality using a log-linear concentration–response function for ozone and an integrated exposure–response model for PM2.5.Results:We estimated 2.23 (95% CI: 1.04, 3.33) million deaths/year related to anthropogenic PM2.5, with the highest mortality in East Asia (48%). The Residential and Commercial sector had the greatest impact globally—675 (95% CI: 428, 899) thousand deaths/year—and in most regions. Land Transportation dominated in North America (32% of total anthropogenic PM2.5 mortality), and it had nearly the same impact (24%) as Residential and Commercial (27%) in Europe. Anthropogenic ozone was associated with 493 (95% CI: 122, 989) thousand deaths/year, with the Land Transportation sector having the greatest impact globally (16%).Conclusions:The contributions of emissions sectors to ambient air pollution–related mortality differ among regions, suggesting region-specific air pollution control strategies. Global sector-specific actions targeting Land Transportation (ozone) and Residential and Commercial (PM2.5) sectors would particularly benefit human health.Citation:Silva RA, Adelman Z, Fry MM, West JJ. 2016. The impact of individual anthropogenic emissions sectors on the global burden of human mortality due to ambient air pollution. Environ Health Perspect 124:1776–1784; http://dx.doi.org/10.1289/EHP177

WRF-Chem 모형을 이용한 한반도 대기질 모의: 화학 초기 및 측면 경계 조건의 영향

There is an increasing need to improve the air quality over South Korea to protect public health from local and remote anthropogenic pollutant emissions that are in an increasing trend. Here, we evaluate the performance of the WRF-Chem (Weather Research and Forecasting-Chemistry) model in simulating near-surface air quality of major Korean cities, and investigate the impacts of time-varying chemical initial and lateral boundary conditions (IC/BCs) on the air quality simulation using a chemical downscaling technique. The model domain was configured over the East Asian region and anthropogenic MICS-Asia 2010 emissions and biogenic MEGAN-2 emissions were applied with RACM gaseous chemistry and MADE/SORGAM aerosol mechanism. Two simulations were conducted for a 30-days period on April 2010 with chemical IC/BCs from the WRF-Chem default chemical species profiles ('WRF experiment') and the MOZART-4 (Model for OZone And Related chemical Tracers version 4) ('WRF_MOZART experiment'), respectively. The WRF_MOZART experiment has showed a better performance to predict near-surface CO, , , and mixing ratios at 7 major Korean cities than the WRF experiment, showing lower mean bias error (MBE) and higher index of agreement (IOA). The quantitative impacts of the chemical IC/BCs have depended on atmospheric residence time of the pollutants as well as the relative difference of chemical mixing ratios between the WRF and WRF_MOZART experiments at the lateral boundaries. Specifically, the WRF_MOZART experiment has reduced MBE in CO and O3 mixing ratios by 60~80 ppb and 5~10 ppb over South Korea than those in the WRF-Chem default simulation, while it has a marginal impact on and mixing ratios. Without using MOZART-4 chemical IC, the WRF simulation has required approximately 6-days chemical spin-up time for the East Asian model domain. Overall, the results indicate that realistic chemical IC/BCs are prerequisite in the WRF-Chem simulation to improve a forecast skill of local air quality over South Korea, even in case the model domain is sufficiently large to represent anthropogenic emissions from China, Japan, and South Korea.

Long-range transport of black carbon to the Pacific Ocean and its dependence on aging timescale

Abstract. Improving the ability of global models to predict concentrations of black carbon (BC) over the Pacific Ocean is essential to evaluate the impact of BC on marine climate. In this study, we tag BC tracers from 13 source regions around the globe in a global chemical transport model, Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4). Numerous sensitivity simulations are carried out varying the aging timescale of BC emitted from each source region. The aging timescale for each source region is optimized by minimizing errors in vertical profiles of BC mass mixing ratios between simulations and HIAPER Pole-to-Pole Observations (HIPPO). For most HIPPO deployments, in the Northern Hemisphere, optimized aging timescales are less than half a day for BC emitted from tropical and midlatitude source regions and about 1 week for BC emitted from high-latitude regions in all seasons except summer. We find that East Asian emissions contribute most to the BC loading over the North Pacific, while South American, African and Australian emissions dominate BC loadings over the South Pacific. Dominant source regions contributing to BC loadings in other parts of the globe are also assessed. The lifetime of BC originating from East Asia (i.e., the world's largest BC emitter) is found to be only 2.2 days, much shorter than the global average lifetime of 4.9 days, making the contribution from East Asia to the global BC burden only 36 % of that from the second largest emitter, Africa. Thus, evaluating only relative emission rates without accounting for differences in aging timescales and deposition rates is not predictive of the contribution of a given source region to climate impacts. Our simulations indicate that the lifetime of BC increases nearly linearly with aging timescale for all source regions. When the aging rate is fast, the lifetime of BC is largely determined by factors that control local deposition rates (e.g., precipitation). The sensitivity of lifetime to aging timescale depends strongly on the initial hygroscopicity of freshly emitted BC. Our findings suggest that the aging timescale of BC varies significantly by region and season and can strongly influence the contribution of source regions to BC burdens around the globe. Therefore, improving parameterizations of the aging process for BC is important for enhancing the predictive skill of global models. Future observations that investigate the evolution of the hygroscopicity of BC as it ages from different source regions to the remote atmosphere are urgently needed.

Acetylene (C<sub>2</sub>H<sub>2</sub>) and hydrogen cyanide (HCN) from IASI satellite observations: global distributions, validation, and comparison with model

Abstract. We present global distributions of C2H2 and hydrogen cyanide (HCN) total columns derived from the Infrared Atmospheric Sounding Interferometer (IASI) for the years 2008–2010. These distributions are obtained with a fast method allowing to retrieve C2H2 abundance globally with a 5 % precision and HCN abundance in the tropical (subtropical) belt with a 10 % (25 %) precision. IASI data are compared for validation purposes with ground-based Fourier transform infrared (FTIR) spectrometer measurements at four selected stations. We show that there is an overall agreement between the ground-based and space measurements with correlation coefficients for daily mean measurements ranging from 0.28 to 0.81, depending on the site. Global C2H2 and subtropical HCN abundances retrieved from IASI spectra show the expected seasonality linked to variations in the anthropogenic emissions and seasonal biomass burning activity, as well as exceptional events, and are in good agreement with previous spaceborne studies. Total columns simulated by the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) are compared to the ground-based FTIR measurements at the four selected stations. The model is able to capture the seasonality in the two species in most of the cases, with correlation coefficients for daily mean measurements ranging from 0.50 to 0.86, depending on the site. IASI measurements are also compared to the distributions from MOZART-4. Seasonal cycles observed from satellite data are reasonably well reproduced by the model with correlation coefficients ranging from −0.31 to 0.93 for C2H2 daily means, and from 0.09 to 0.86 for HCN daily means, depending on the considered region. However, the anthropogenic (biomass burning) emissions used in the model seem to be overestimated (underestimated), and a negative global mean bias of 1 % (16 %) of the model relative to the satellite observations was found for C2H2 (HCN).

Identifying fire plumes in the Arctic with tropospheric FTIR measurements and transport models

Abstract. We investigate Arctic tropospheric composition using ground-based Fourier transform infrared (FTIR) solar absorption spectra, recorded at the Polar Environment Atmospheric Research Laboratory (PEARL, Eureka, Nunavut, Canada, 80°05' N, 86°42' W) and at Thule (Greenland, 76°53' N, −68°74' W) from 2008 to 2012. The target species, carbon monoxide (CO), hydrogen cyanide (HCN), ethane (C2H6), acetylene (C2H2), formic acid (HCOOH), and formaldehyde (H2CO) are emitted by biomass burning and can be transported from mid-latitudes to the Arctic. By detecting simultaneous enhancements of three biomass burning tracers (HCN, CO, and C2H6), ten and eight fire events are identified at Eureka and Thule, respectively, within the 5-year FTIR time series. Analyses of Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model back-trajectories coupled with Moderate Resolution Imaging Spectroradiometer (MODIS) fire hotspot data, Stochastic Time-Inverted Lagrangian Transport (STILT) model footprints, and Ozone Monitoring Instrument (OMI) UV aerosol index maps, are used to attribute burning source regions and travel time durations of the plumes. By taking into account the effect of aging of the smoke plumes, measured FTIR enhancement ratios were corrected to obtain emission ratios and equivalent emission factors. The means of emission factors for extratropical forest estimated with the two FTIR data sets are 0.40 ± 0.21 g kg−1 for HCN, 1.24 ± 0.71 g kg−1 for C2H6, 0.34 ± 0.21 g kg−1 for C2H2, and 2.92 ± 1.30 g kg−1 for HCOOH. The emission factor for CH3OH estimated at Eureka is 3.44 ± 1.68 g kg−1. To improve our knowledge concerning the dynamical and chemical processes associated with Arctic pollution from fires, the two sets of FTIR measurements were compared to the Model for OZone And Related chemical Tracers, version 4 (MOZART-4). Seasonal cycles and day-to-day variabilities were compared to assess the ability of the model to reproduce emissions from fires and their transport. Good agreement in winter confirms that transport is well implemented in the model. For C2H6, however, the lower wintertime concentration estimated by the model as compared to the FTIR observations highlights an underestimation of its emission. Results show that modeled and measured total columns are correlated (linear correlation coefficient r > 0.6 for all gases except for H2CO at Eureka and HCOOH at Thule), but suggest a general underestimation of the concentrations in the model for all seven tropospheric species in the high Arctic.

Improving the representation of secondary organic aerosol (SOA) in the MOZART-4 global chemical transport model

Abstract. The secondary organic aerosol (SOA) module in the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) was updated by replacing existing two-product (2p) parameters with those obtained from two-product volatility basis set (2p-VBS) fits (MZ4-C1), and by treating SOA formation from the following additional volatile organic compounds (VOCs): isoprene, propene and lumped alkenes (MZ4-C2). Strong seasonal and spatial variations in global SOA distributions were demonstrated, with significant differences in the predicted concentrations between the base case and updated model simulations. Updates to the model resulted in significant increases in annual average SOA mass concentrations, particularly for the MZ4-C2 simulation in which the additional SOA precursor VOCs were treated. Annual average SOA concentrations predicted by the MZ4-C2 simulation were 1.00 ± 1.04 μg m−3 in South America, 1.57 ± 1.88 μg m−3 in Indonesia, 0.37 ± 0.27 μg m−3 in the USA, and 0.47 ± 0.29 μg m−3 in Europe with corresponding increases of 178, 406, 311 and 292% over the base-case simulation, respectively, primarily due to inclusion of isoprene. The increases in predicted SOA mass concentrations resulted in corresponding increases in SOA contributions to annual average total aerosol optical depth (AOD) by ~ 1–6%. Estimated global SOA production was 5.8, 6.6 and 19.1 Tg yr−1 with corresponding burdens of 0.22, 0.24 and 0.59 Tg for the base-case, MZ4-C1 and MZ4-C2 simulations, respectively. The predicted SOA budgets fell well within reported ranges for comparable modeling studies, 6.7 to 96 Tg yr−1, but were lower than recently reported observationally constrained values, 50 to 380 Tg yr−1. For MZ4-C2, simulated SOA concentrations at the surface also were in reasonable agreement with comparable modeling studies and observations. Total organic aerosol (OA) mass concentrations at the surface, however, were slightly over-predicted in Europe, Amazonian regions and Malaysian Borneo (Southeast Asia) during certain months of the year, and under-predicted in most sites in Asia; relative to those regions, the model performed better for sites in North America. Overall, with the inclusion of additional SOA precursors (MZ4-C2), namely isoprene, MOZART-4 showed consistently better skill (NMB (normalized mean bias) of −11 vs. −26%) in predicting total OA levels and spatial distributions of SOA as compared with unmodified MOZART-4. Treatment of SOA formation by these known precursors (isoprene, propene and lumped alkenes) may be particularly important when MOZART-4 output is used to generate boundary conditions for regional air quality simulations that require more accurate representation of SOA concentrations and distributions.

Estimate of methane release from temperate natural wetlands using ENVISAT/SCIAMACHY data in China

Since wetlands are the largest natural sources of atmospheric CH4, it is important to estimate the CH4 emissions from natural wetlands at regional scale and over a long time period. The annual CH4 efflux from temperate natural wetlands excluding water surface in China was estimated, based on atmospheric CH4 concentrations from SCIAMACHY/ENVISAT. The atmospheric CH4 concentrations showed obvious seasonal cycles, and CH4 emission from natural wetlands dominated the temporal variations of CH4 concentrations in north China, accounting for about 67.94% of the variations of CH4 concentrations. The chemical transport model, MOZART-4 (Model for Ozone and Related Chemical Tracers, version 4), was used to simulate the space-borne CH4 column concentrations to the surface level, and then the relationship between surface concentrations and emissions of CH4 from natural wetlands was simulated by a linear regression model. The results showed that the estimated annual budget of CH4 emission from natural wetlands in the temperate zone of China was about 4.76 Tg CH4, which was within the range of 2.38–4.91 Tg CH4 estimated by spatial distribution of wetland and the published CH4 release fluxes during the 1990s–2000s. This demonstrated that the method of using space-borne CH4 column concentrations to estimate CH4 emissions from natural wetlands was reliable.

Case study of the diurnal variability of chemically active species with respect to boundary layer dynamics during DOMINO

Abstract. We study the interactions between atmospheric boundary layer (ABL) dynamics and atmospheric chemistry using a mixed-layer model coupled to chemical reaction schemes. Guided by both atmospheric and chemical measurements obtained during the DOMINO (Diel Oxidant Mechanisms in relation to Nitrogen Oxides) campaign (2008), numerical experiments are performed to study the role of ABL dynamics and the accuracy of chemical schemes with different complexity: the Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) and a reduced mechanism of this chemical system. Both schemes produce satisfactory results, indicating that the reduced scheme is capable of reproducing the O3-NOx-VOC-HOx diurnal cycle during conditions characterized by a low NOx regime and small O3 tendencies (less than 1 ppb per hour). By focusing on the budget equations of chemical species in the mixed-layer model, we show that for species like O3, NO and NO2, the influence of entrainment and boundary layer growth is of the same order as chemical production/loss. This indicates that an accurate representation of ABL processes is crucial in understanding the diel cycle of chemical species. By comparing the time scales of chemical reactive species with the mixing time scale of turbulence, we propose a classification based on the Damköhler number to further determine the importance of dynamics on chemistry during field campaigns. Our findings advocate an integrated approach, simultaneously solving the ABL dynamics and chemical reactions, in order to obtain a better understanding of chemical pathways and processes and the interpretation of the results obtained during measurement campaigns.

Analysis of ozone and nitric acid in spring and summer Arctic pollution using aircraft, ground-based, satellite observations and MOZART-4 model: source attribution and partitioning

Abstract. In this paper, we analyze tropospheric O3 together with HNO3 during the POLARCAT (Polar Study using Aircraft, Remote Sensing, Surface Measurements and Models, of Climate, Chemistry, Aerosols, and Transport) program, combining observations and model results. Aircraft observations from the NASA ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and NOAA ARCPAC (Aerosol, Radiation and Cloud Processes affecting Arctic Climate) campaigns during spring and summer of 2008 are used together with the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) to assist in the interpretation of the observations in terms of the source attribution and transport of O3 and HNO3 into the Arctic (north of 60° N). The MOZART-4 simulations reproduce the aircraft observations generally well (within 15%), but some discrepancies in the model are identified and discussed. The observed correlation of O3 with HNO3 is exploited to evaluate the MOZART-4 model performance for different air mass types (fresh plumes, free troposphere and stratospheric-contaminated air masses). Based on model simulations of O3 and HNO3 tagged by source type and region, we find that the anthropogenic pollution from the Northern Hemisphere is the dominant source of O3 and HNO3 in the Arctic at pressures greater than 400 hPa, and that the stratospheric influence is the principal contribution at pressures less 400 hPa. During the summer, intense Russian fire emissions contribute some amount to the tropospheric columns of both gases over the American sector of the Arctic. North American fire emissions (California and Canada) also show an important impact on tropospheric ozone in the Arctic boundary layer. Additional analysis of tropospheric O3 measurements from ground-based FTIR and from the IASI satellite sounder made at the Eureka (Canada) and Thule (Greenland) polar sites during POLARCAT has been performed using the tagged contributions. It demonstrates the capability of these instruments for observing pollution at northern high latitudes. Differences between contributions from the sources to the tropospheric columns as measured by FTIR and IASI are discussed in terms of vertical sensitivity associated with these instruments. The first analysis of O3 tropospheric columns observed by the IASI satellite instrument over the Arctic is also provided. Despite its limited vertical sensitivity in the lowermost atmospheric layers, we demonstrate that IASI is capable of detecting low-altitude pollution transported into the Arctic with some limitations.

Impact of Mexico City emissions on regional air quality from MOZART-4 simulations

Abstract. An extensive set of measurements was made in and around Mexico City as part of the MILAGRO (Megacity Initiative: Local and Global Research Observations) experiments in March 2006. Simulations with the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4), a global chemical transport model, have been used to provide a regional context for these observations and assist in their interpretation. These MOZART-4 simulations reproduce the aircraft observations generally well, but some differences in the modeled volatile organic compounds (VOCs) from the observations result from incorrect VOC speciation assumed for the emission inventories. The different types of CO sources represented in the model have been "tagged" to quantify the contributions of regions outside Mexico, as well as the various emissions sectors within Mexico, to the regional air quality of Mexico. This analysis indicates open fires have some, but not a dominant, impact on the atmospheric composition in the region around Mexico City when averaged over the month. However, considerable variation in the fire contribution (2–15% of total CO) is seen during the month. The transport and photochemical aging of Mexico City emissions were studied using tags of CO emissions for each day, showing that typically the air downwind of Mexico City was a combination of many ages. Ozone production in MOZART-4 is shown to agree well with the net production rates from box model calculations constrained by the MILAGRO aircraft measurements. Ozone production efficiency derived from the ratio of Ox to NOz is higher in MOZART-4 than in the observations for moderately polluted air. OH reactivity determined from the MOZART-4 results shows the same increase in relative importance of oxygenated VOCs downwind of Mexico City as the reactivity inferred from the observations. The amount of ozone produced by emissions from Mexico City and surrounding areas has been quantified in the model by tracking NO emissions, showing little influence beyond Mexico's borders, and also relatively minor influence from fire emissions on the monthly average tropospheric ozone column.