Measurements Of Pollution In The Troposphere CO Research Articles

Validation and analysis of MOPITT CO observations of the Amazon Basin

Abstract. We analyze satellite retrievals of carbon monoxide from the MOPITT (Measurements of Pollution in the Troposphere) instrument over the Amazon Basin, focusing on the MOPITT Version 6 "multispectral" retrieval product (exploiting both thermal-infrared and near-infrared channels). Validation results based on in situ vertical profiles measured between 2010 and 2013 are presented for four sites in the Amazon Basin. Results indicate a significant negative bias in retrieved lower-tropospheric CO concentrations. The possible influence of smoke aerosol as a source of retrieval bias is investigated using collocated Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) measurements at two sites but does not appear to be significant. Finally, we exploit the MOPITT record to analyze both the mean annual cycle and the interannual variability of CO over the Amazon Basin since 2002.

High-resolution tropospheric carbon monoxide profiles retrieved from CrIS and TROPOMI

Abstract. The Measurements of Pollution in the Troposphere (MOPITT) instrument is the only satellite-borne sensor in operation that uses both thermal (TIR) and near-infrared (NIR) channels to estimate CO profiles. With more than 15 years (2000 to present) of validated multispectral observations, MOPITT provides the unique capability to separate CO in the lowermost troposphere (LMT, surface to 3 km (∼ 700 hPa)) from the free-tropospheric abundance. To extend this record, a new, hyper-spectral approach is presented here that will provide CO data products exceeding the capabilities of MOPITT by combining the short-wavelength infrared (SWIR, equivalent to the MOPITT NIR) channels from the TROPOspheric Monitoring Instrument (TROPOMI) to be launched aboard the European Sentinel 5 Precursor (S5p) satellite in 2016 and the TIR channels from the Cross-track Infrared Sounder (CrIS) aboard the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite. We apply the MUlti-SpEctra, MUlti-SpEcies, Multi-SEnsors (MUSES) retrieval algorithm to quantify the potential of this joint CO product. CO profiles are retrieved from a single-footprint, full-spectral-resolution CrIS transect over Africa on 27–28 August 2013 coincident with significant biomass burning. Comparisons of collocated CrIS and MOPITT CO observations for the LMT show a mean difference of 2.8 ± 24.9 ppb, which is well within the estimated measurement uncertainty of both sensors. The estimated degrees of freedom (DOF) for CO signals from synergistic CrIS–TROPOMI retrievals are approximately 0.9 in the LMT and 1.3 above the LMT, which indicates that the LMT CO can be distinguished from the free troposphere, similar to MOPITT multispectral observations (0.8 in the LMT, and 1.1 above the LMT). In addition to increased sensitivity, the combined retrievals reduce measurement uncertainty, with ∼ 15 % error reduction in the LMT. With a daily global coverage and a combined spatial footprint of 14 km, the joint CrIS–TROPOMI measurements have the potential to extend and improve upon the MOPITT multispectral CO data records for the coming decade.

Assessing the impacts of assimilating IASI and MOPITT CO retrievals using CESM‐CAM‐chem and DART

AbstractWe show the results and evaluation with independent measurements from assimilating both MOPITT (Measurements Of Pollution In The Troposphere) and IASI (Infrared Atmospheric Sounding Interferometer) retrieved profiles into the Community Earth System Model (CESM). We used the Data Assimilation Research Testbed ensemble Kalman filter technique, with the full atmospheric chemistry CESM component Community Atmospheric Model with Chemistry. We first discuss the methodology and evaluation of the current data assimilation system with coupled meteorology and chemistry data assimilation. The different capabilities of MOPITT and IASI retrievals are highlighted, with particular attention to instrument vertical sensitivity and coverage and how these impact the analyses. MOPITT and IASI CO retrievals mostly constrain the CO fields close to the main anthropogenic, biogenic, and biomass burning CO sources. In the case of IASI CO assimilation, we also observe constraints on CO far from the sources. During the simulation time period (June and July 2008), CO assimilation of both instruments strongly improves the atmospheric CO state as compared to independent observations, with the higher spatial coverage of IASI providing better results on the global scale. However, the enhanced sensitivity of multispectral MOPITT observations to near surface CO over the main source regions provides synergistic effects at regional scales.

Comparison of upper tropospheric carbon monoxide from MOPITT, ACE‐FTS, and HIPPO‐QCLS

AbstractProducts from the Measurements Of Pollution In The Troposphere (MOPITT) instrument are regularly validated using in situ airborne measurements. However, few of these measurements reach into the upper troposphere, thus hindering MOPITT validation in that region. Here we evaluate upper tropospheric (~500 hPa to the tropopause) MOPITT CO profiles by comparing them to satellite Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE‐FTS) retrievals and to measurements from the High‐performance Instrumented Airborne Platform for Environmental Research Pole to Pole Observations (HIPPO) Quantum Cascade Laser Spectrometer (QCLS). Direct comparison of colocated v5 MOPITT thermal infrared‐only retrievals, v3.0 ACE‐FTS retrievals, and HIPPO‐QCLS measurements shows a slight positive MOPITT CO bias within its 10% accuracy requirement with respect to the other two data sets. Direct comparison of colocated ACE‐FTS and HIPPO‐QCLS measurements results in a small number of samples due to the large disparity in sampling pattern and density of these data sets. Thus, two additional indirect techniques for comparison of noncoincident data sets have been applied: tracer‐tracer (CO‐O3) correlation analysis and analysis of profiles in tropopause coordinates. These techniques suggest a negative bias of ACE‐FTS with respect to HIPPO‐QCLS; this could be caused by differences in resolution (horizontal, vertical) or by deficiencies in the ACE‐FTS CO retrievals below ~20 km of altitude, among others. We also investigate the temporal stability of MOPITT and ACE‐FTS data, which provide unique global CO records and are thus important in climate analysis. Our results indicate that the relative bias between the two data sets has remained generally stable during the 2004–2010 period.

Diagnosing the transition layer at extratropical latitudes using MLS O<sub>3</sub> and MOPITT CO analyses

Abstract. The behavior of the extratropical transition layer (ExTL) is investigated using a chemistry transport model (CTM) and analyses derived from assimilation of MLS (Microwave Limb Sounder) O3 and MOPITT (Measurements Of Pollution In The Troposphere) CO data. We firstly focus on a stratosphere–troposphere exchange (STE) case study that occurred on 15 August 2007 over the British Isles (50° N, 10° W). We evaluate the effect of data assimilation on the O3–CO correlations. It is shown that data assimilation disrupts the relationship in the transition region. When MLS O3 is assimilated, CO and O3 values are not consistent between each other, leading to unphysical correlations at the STE location. When MLS O3 and MOPITT CO assimilated fields are taken into account in the diagnostics the relationship happens to be more physical. We then use O3–CO correlations to quantify the effect of data assimilation on the height and depth of the ExTL. When the free-model run O3 and CO fields are used in the diagnostics, the ExTL distribution is found 1.1 km above the thermal tropopause and is 2.6 km wide (2σ). MOPITT CO analyses only slightly sharpen (by −0.02 km) and lower (by −0.2 km) the ExTL distribution. MLS O3 analyses provide an expansion (by +0.9 km) of the ExTL distribution, suggesting a more intense O3 mixing. However, the MLS O3 analyses ExTL distribution shows a maximum close to the thermal tropopause and a mean location closer to the thermal tropopause (+0.45 km). When MLS O3 and MOPITT CO analyses are used together, the ExTL shows a mean location that is the closest to the thermal tropopause (+0.16 km). We also extend the study at the global scale on 15 August 2007 and for the month of August 2007. MOPITT CO analyses still show a narrower chemical transition between stratosphere and troposphere than the free-model run. MLS O3 analyses move the ExTL toward the troposphere and broaden it. When MLS O3 analyses and MOPITT CO analyses are used together, the ExTL matches the thermal tropopause poleward of 50°.

Mean global and regional distributions of MOPITT carbon monoxide during 2000–2009 and during ENSO

Abstract The MOPITT (Measurements Of Pollution In The Troposphere) CO measurements over a 10-year period (2000–2009) reveal consistently positive trends on the order of 0.13–0.19 × 10 16 mol cm −2 per month in CO total column concentrations over the entire globe and the hemispheres. Two maxima in globally averaged CO concentrations are identified: one in April and one in October, with two minima in July and December. These maxima and minima are attributable to the respective maxima and minima in CO concentrations over the Northern and Southern Hemispheres. Over the Tropics, maximum and minimum CO concentrations are noted in October and June, respectively, due primarily to biomass burning. During El Nino DJF (December–January–February) and JJA (June–July–August), predominantly positive anomalies in CO total column are noted over the entire globe except for the high latitudes of both hemispheres and the central part of the South America where negative anomalies are identified. La Nina DJF and JJA are largely opposite to El Nino DJF and JJA in CO total column anomalies. Negative (positive) anomalies in CO total column tend to be associated with wet (dry) anomalies in precipitation over the major polluted areas during ENSO. It is suggested that changes in the atmospheric circulations during ENSO either enhance or weaken precipitation systems with the associated precipitation modulating CO total column. The correspondence between anomalies in CO total column and anomalies in Terra MODIS fire pixels during ENSO is rather poor over many parts of the world.

Global AIRS and MOPITT CO measurements: Validation, comparison, and links to biomass burning variations and carbon cycle

New results of CO global total column measurements using the Atmospheric Infrared Sounder (AIRS) aboard the Aqua satellite in comparison with Measurements of Pollution in the Troposphere (MOPITT) sensor aboard the Terra satellite are presented. Both data sets are validated using ground‐based total column measurements in Russia and Australia. A quality parameter based on the Profile Percent A Priori values from the standard MOPITT product is introduced. AIRS data (version 4) for biomass burning events are in agreement or lower than both MOPITT and ground measurements, but CO bursts can be seen by AIRS in most cases. For the cases of low CO amounts in the Southern Hemisphere AIRS has a positive bias of ∼30–40% compared to MOPITT and ground truth. MOPITT data were used to estimate interannual variations of CO sources assuming a standard seasonal cycle for the main CO remover OH. A positive trend of CO global emissions for the second half of the year between 2000 and 2006 was found with no visible trend for the first half of the year. CO annual emission in 2006 was 184 ± 40 Tg higher that that in 2000–2001. The monthly emission anomalies correlate well with an independently calculated Global Fire Emission Database (GFED2). Total carbon contribution from biomass burning in 1997, 1998 (both estimated by GFED2), and 2006 (according to MOPITT) were as high as (0.6–1) Pg C/year larger than in 2000, suggesting that fires can explain a substantial fraction of the interannual variability of CO2.

Satellite observations of aerosol and CO over Mexico City

The development of remote sensing satellite technology potentially will lead to the technical means to monitor air pollution emitted from large cities on a global basis. This paper presents observations by the moderate resolution imaging spectroradiometer (MODIS) and measurements of pollution in the troposphere (MOPITT) experiments of aerosol optical depths and CO mixing ratios, respectively, in the vicinity of Mexico City to illustrate current satellite capabilities. MOPITT CO mixing ratios over Mexico City, averaged between January–March 2002–2005, are 19% above regional values and the CO plume extends over 10° 2 in the free troposphere at 500 hPa. Time series of Red Automatica de Monitoreo Ambiental (RAMA) PM10, and (Aerosol Robotic Network) AERONET and MODIS aerosol optical depths, and RAMA and MOPITT CO time series are inter-compared to illustrate the different perspectives of ground based and satellite instrumentation. Finally, we demonstrate, by examining MODIS and MOPITT data in April 2003, that satellite data can be used to identify episodes in which pollution form fires influences the time series of ground based and satellite observations of urban pollution.

Large horizontal gradients in atmospheric CO at the synoptic scale as seen by spaceborne Measurements of Pollution in the Troposphere

We have examined the influence of synoptic processes on the distribution of atmospheric CO as observed by the Measurements of Pollution in the Troposphere (MOPITT) satellite instrument. In the MOPITT data, large horizontal gradients in CO, coherent at the synoptic scale, have been observed. The concentration of CO varies rapidly by as much as 50–100% across distances of ∼100 km, forming distinct boundaries in the CO distribution. These can last one to several days and span horizontal distances of 600–1000 km. On average, such events were observed in the MOPITT CO daily images once every 3–4 days over North America in spring and summer 2000. We focused on three case studies over North America in August 2000 to understand the mechanisms responsible for the large gradients in CO. Through an analysis of meteorological data from the National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis, parcel trajectory modeling, and global three‐dimensional chemical transport modeling, we found that the large horizontal gradients typically reflect the differential vertical and horizontal transport of air with different chemical signatures. In the first case, the large gradients in CO over North Dakota resulted from the lifting ahead of a cold front that transported boundary layer air enriched with CO from forest fires in Montana, combined with the descent of clean air from the Canadian Prairies behind the front. In the second case, the large gradients over northeastern Texas were produced by the convective lifting over Arkansas of air with high concentrations of CO from the oxidation of volatile organic compounds and the onshore transport of clean air from the Gulf of Mexico. In the third case, we examined an example of outflow of surface pollution from North America by a cyclone. The largest gradients in this case were observed along the boundary between the boundary layer air transported by the warm conveyor belt ahead of the cold front and the clean air transported from the Atlantic by the semipermanent high‐pressure system in the central Atlantic. Our results demonstrate that MOPITT can capture the influence of synoptic processes on the horizontal and vertical distribution of CO. The large gradients in CO observed on synoptic scales represent valuable information that can be exploited to improve our understanding of atmospheric CO. In particular, these results suggest that the MOPITT observations provide a useful data set with which to address a range of issues from air quality on local/regional scales to long‐range transport of pollution on continental/global scales.

Vertical resolution and information content of CO profiles retrieved by MOPITT

The MOPITT (Measurements of Pollution in the Troposphere) remote sensing instrument monitors the global distribution of carbon monoxide from a polar‐orbiting platform. Calculated averaging kernels for operational MOPITT CO profiles indicate the capability of independently retrieving mid‐ and upper‐tropospheric CO. The information content in MOPITT retrievals is objectively quantified through calculation of the Degrees of Freedom for Signal (DFS), which indicates the number of independent pieces of information in the retrieved profile. DFS values larger than 1 (indicating some amount of profile shape information) are common in tropical and midlatitude scenes. The existence of shape information in actual MOPITT retrieved profiles is also verified through (1) a quantitative comparison with in‐situ data acquired as part of MOPITT validation and (2) a qualitative comparison with monthly mean rain rate (as an index for convection) in the Tropical Eastern Pacific Ocean.