Tropospheric Ozone Precursors Research Articles

A multi-regional input-output analysis of ozone precursor emissions embodied in Spanish international trade

Higher levels of ozone in the troposphere is a severe threat to both environment and human health. Many countries are concerned about the effects that critical levels of ozone have on them. Countries pollute to satisfy their domestic and external demand (production perspective) and, at the same time, these countries also generate emissions abroad indirectly via their imports and via their domestic production (consumption perspective). Spain is one of the EU countries with the highest pollution records in the emissions of tropospheric ozone precursor gases. A multiregional input-output model (MRIO) allows us to analyze the total emissions embodied in Spanish international trade in 35 sectors within the EU area and the rest of the world. MRIO models, are commonly chosen as they provide an appropriate methodological framework for complete emissions footprint estimates at the national and supranational level The results show that the most polluting sectors involved in Spanish trade are Agriculture, Basic Metals, Coke and Refined Petroleum Production. Some policy recommendations follow these results; for example, a higher number of environmental regulations focused on the Agricultural sector, such as the introduction of codes of good practices in the use of fertilizers and the promotion of cleaner production technologies might lead to less burden to the environment.

Spatiotemporal patterns and source implications of aromatic hydrocarbons at six rural sites across China's developed coastal regions

AbstractAromatic hydrocarbons are important anthropogenic precursors of tropospheric ozone and secondary organic aerosols. Here we measured ambient aromatic hydrocarbons from March 2012 to February 2014 at six rural sites in China's developed coastal regions. On average, benzene (B) comprised > 50% of total benzene (B), toluene (T), ethylbenzene (E), and xylenes (X) (BTEX) at sites in the Northeast China Plain (NECP) or in the North China Plain (NCP), whereas T, E, and X accounted for > 77% of total BTEX at sites in the Yangtze River Delta (YRD) and the Pearl River Delta in the south. BTEX at the northern sites was significantly correlated (p < 0.01) with combustion tracer‐carbon monoxide (CO) but weakly correlated with traffic marker‐methyl tert‐butyl ether (MTBE), suggesting that their main sources were coal and biofuel/biomass burning with substantially elevated B levels during the winter heating period. In contrast, BTEX at the southern sites originated mainly from traffic‐related and/or industrial emission sources, as indicated by the poor correlations with CO but highly significant (p < 0.01) correlations with MTBE and tetrachloroethylene, an industrial emission tracer. The B/CO emission ratios from measurement agreed within a factor of 2 with that of a previous widely used emission inventory of China, but the T/CO ratio at the NECP site and the o‐X/CO ratio at the NCP site were 29% and 38% of that in the inventory, respectively; the E/CO and X/CO ratios at the YRD site were 3.2–3.5 fold that in the emission inventory.

Observations of atmospheric monoaromatic hydrocarbons at urban, semi-urban and forest environments in the Amazon region

Abstract The Amazon region is one of the most significant natural ecosystems on the planet. Of special interest as a major study area is the interface between the forest and Manaus city, a state capital in Brazil embedded in the heart of the Amazon forest. In view of the interactions between natural and anthropogenic processes, an integrated experiment was conducted measuring the concentrations of the volatile organic compounds (VOCs) benzene, toluene, ethylbenzene and meta, ortho, para-xylene (known as BTEX), all of them regarded as pollutants with harmful effects on human health and vegetation and acting also as important precursors of tropospheric ozone. Furthermore, these compounds also take part in the formation of secondary organic aerosols, which can influence the pattern of cloud formation, and thus the regional water cycle and climate. The samples were collected in 2012/2013 at three different sites: (i) The Amazon Tall Tower Observatory (ATTO), a pristine rain forest region in the central Amazon Basin; (ii) Manacapuru, a semi-urban site located southwest and downwind of Manaus as a preview of the Green Ocean Amazon Experiment (GoAmazon 2014/15); and (iii) the city of Manaus (distributed over three sites). Results indicate that there is an increase in pollutant concentrations with increasing proximity to urban areas. For instance, the benzene concentration ranges were 0.237–19.6 (Manaus), 0.036–0.948 (Manacapuru) and 0.018–0.313 μg m −3 (ATTO). Toluene ranges were 0.700–832 (Manaus), 0.091–2.75 μg m −3 (Manacapuru) and 0.011–4.93 (ATTO). For ethylbenzene, they were 0.165–447 (Manaus), 0.018–1.20 μg m −3 (Manacapuru) and 0.047–0.401 (ATTO). Some indication was found for toluene to be released from the forest. No significant difference was found between the BTEX levels measured in the dry season and the wet seasons. Furthermore, it was observed that, in general, the city of Manaus seems to be less impacted by these pollutants than other cities in Brazil and in other countries, near the coastline or on the continent. A risk analysis for the health of Manaus' population was performed and indicated that the measured concentrations posed a risk for development of chronic diseases and cancer for the population of Manaus.

Ozone attributed to Madrid and Barcelona on-road transport emissions: Characterization of plume dynamics over the Iberian Peninsula

Despite the ~30% emission decrease of the main tropospheric ozone (O3) precursors in Spain in the 2001–2012 period, the O3 concentration in summer still exceeds the target value for the protection of the human health of the Air Quality Directive (2008/50/EC). On-road transport is the main anthropogenic contributor to O3 precursor's emissions in Madrid and Barcelona metropolitan areas (65%/59% of NOx, 40%/33% of NMVOC, and 67%/85% of CO emissions) but this contribution to O3 formation is not well understood. The present work aims at increasing the understanding on the role of on-road transport emissions from main Spanish urban areas in O3 dynamics over Spain under typical circulation types. For that purpose, the Integrated Source Apportionment Method is used within the CALIOPE modelling system (WRF/CMAQ/HERMES/BSC-DREAM8b). The results indicate that the daily maximum O3 concentration attributed to the on-road transport emissions from Madrid (O3T-MAD) and Barcelona metropolitan areas (O3T-BCN) contribute up to 24% and 8% to total O3 concentration, respectively, within an area of influence of 200km. The contribution of O3T-MAD and O3T-BCN is particularly significant (up to 80–100μgm−3 in an hour) to the O3 concentration peak during the central hours of the day in the high O3 concentration season (April–September). The maximum O3T-MAD concentration is calculated within the metropolitan area of Madrid but the plume, channelled by the Tajo and the Henares valleys, affects large areas of the Iberian Peninsula. The O3T-BCN plume is more driven by sea-land and mountain-valley breezes than by the synoptic advection and its maximum concentration is usually registered over the Mediterranean Sea. The O3 concentration transported long-range to the Iberian Peninsula is significant in the area of influence of Madrid and Barcelona, being maxima under cold (70–96%) and minima in warm circulation types (35–70%).

Forest-atmosphere BVOC exchange in diverse and structurally complex canopies: 1-D modeling of a mid-successional forest in northern Michigan

Foliar emissions of biogenic volatile organic compounds (BVOC)—important precursors of tropospheric ozone and secondary organic aerosols—vary widely by vegetation type. Modeling studies to date typically represent the canopy as a single dominant tree type or a blend of tree types, yet many forests are diverse with trees of varying height. To assess the sensitivity of biogenic emissions to tree height variation, we compare two 1-D canopy model simulations in which BVOC emission potentials are homogeneous or heterogeneous with canopy depth. The heterogeneous canopy emulates the mid-successional forest at the University of Michigan Biological Station (UMBS). In this case, high-isoprene-emitting foliage (e.g., aspen and oak) is constrained to the upper canopy, where higher sunlight availability increases the light-dependent isoprene emission, leading to 34% more isoprene and its oxidation products as compared to the homogeneous simulation. Isoprene declines from aspen mortality are 10% larger when heterogeneity is considered. Overall, our results highlight the importance of adequately representing complexities of forest canopy structure when simulating light-dependent BVOC emissions and chemistry.

Life cycle impact assessment of ammonia production in Algeria: A comparison with previous studies

In this paper, a Life Cycle Analysis (LCA) from “cradle to gate” of one anhydrous ton of ammonia with a purity of 99% was achieved. Particularly, the energy and environmental performance of the product (ammonia) were evaluated. The eco-profile of the product and the share of each stage of the Life Cycle on the whole environmental impacts have been evaluated. The flows of material and energy for each phase of the life cycle were counted and the associated environmental problems were identified. Evaluation of the impact was achieved using GEMIS 4.7 software. The primary data collection was executed at the production installations located in Algeria (Annaba locality). The analysis was conducted according to the LCA standards ISO 14040 series. The results show that Cumulative Energy Requirement (CER) is of 51.945×103MJ/t of ammonia, which is higher than the global average. Global Warming Potential (GWP) is of 1.44t CO2 eq/t of ammonia; this value is lower than the world average. Tropospheric ozone precursor and Acidification are also studied in this article, their values are: 549.3×10−6t NMVOC eq and 259.3×10−6t SO2 eq respectively.

Demonstration of an ethane spectrometer for methane source identification.

Methane is an important greenhouse gas and tropospheric ozone precursor. Simultaneous observation of ethane with methane can help identify specific methane source types. Aerodyne Ethane-Mini spectrometers, employing recently available mid-infrared distributed feedback tunable diode lasers (DFB-TDL), provide 1 s ethane measurements with sub-ppb precision. In this work, an Ethane-Mini spectrometer has been integrated into two mobile sampling platforms, a ground vehicle and a small airplane, and used to measure ethane/methane enhancement ratios downwind of methane sources. Methane emissions with precisely known sources are shown to have ethane/methane enhancement ratios that differ greatly depending on the source type. Large differences between biogenic and thermogenic sources are observed. Variation within thermogenic sources are detected and tabulated. Methane emitters are classified by their expected ethane content. Categories include the following: biogenic (<0.2%), dry gas (1-6%), wet gas (>6%), pipeline grade natural gas (<15%), and processed natural gas liquids (>30%). Regional scale observations in the Dallas/Fort Worth area of Texas show two distinct ethane/methane enhancement ratios bridged by a transitional region. These results demonstrate the usefulness of continuous and fast ethane measurements in experimental studies of methane emissions, particularly in the oil and natural gas sector.

Strong chemistry‐climate feedbacks in the Pliocene

AbstractThe Pliocene epoch was the last sustained interval when global climate was significantly warmer than today but has been difficult to explain fully based on the external forcings from atmospheric carbon dioxide and surface albedo. Here we use an Earth system model to simulate terrestrial ecosystem emissions and atmospheric chemical composition in the mid‐Pliocene (about 3 million years ago) and the preindustrial (~1750s). Tropospheric ozone and aerosol precursors from vegetation and wildfire are ~50% and ~100% higher in the mid‐Pliocene due to the spread of the tropical savanna and deciduous biomes. The chemistry‐climate feedbacks contribute a net global warming that is +30–250% of the carbon dioxide effect and a net aerosol global cooling that masks 15–100% of the carbon dioxide effect. These large vegetation‐mediated ozone and aerosol feedbacks operate on centennial to millennial timescales in the climate system and have not previously been included in paleoclimate sensitivity assessments.

Contributions to twentieth century total column ozone change from halocarbons, tropospheric ozone precursors, and climate change

We investigate ozone changes from preindustrial times to the present using a chemistry‐climate model. The influence of changes in physical climate, ozone‐depleting substances, N2O, and tropospheric ozone precursors is estimated using equilibrium simulations with these different factors set at either preindustrial or present‐day values. When these effects are combined, the entire decrease in total column ozone from preindustrial to present day is very small (−1.8 DU) in the global annual average, though with significant decreases in total column ozone over large parts of the Southern Hemisphere during austral spring and widespread increases in column ozone over the Northern Hemisphere during boreal summer. A significant contribution to the total ozone column change is the increase in lower stratospheric ozone associated with the increase in ozone precursors (5.9 DU). Also noteworthy is the near cancelation of the global average climate change effect on ozone (3.5 DU) by the increase in N2O (−3.9 DU).

Ozone trends in the vertical structure of Upper Troposphere and Lower stratosphere over the Indian monsoon region

Ozone trends in the Upper Troposphere and Lower Stratosphere over the Indian region are investigated using three satellite data sets namely Halogen Occultation Experiment (1993–2005), Stratospheric Aerosol and Gas Experiment (1993–2005) II, and Aura Microwave Limb Sounder (MLS, 2005–2011). Estimated ozone trends using multi-variate regression analysis are compared with trends at two Indian ozonesonde stations (Delhi, 28°N, 77°E and Pune, 18°N, 73°E), and a 3-D Chemical Transport Model (CTM, SLIMCAT) for the 1993–2005 time period. Overall, all the observational data sets and model simulations indicate significant increasing trend in the upper troposphere (0–2.5 %/year). In the lower stratosphere, estimated trends are slightly positive up to 30 mb and are negative between 30 and 10 mb. Increasing trends in the upper troposphere is probably due to increasing trends in the tropospheric ozone precursor gases (e.g. CO, NO x , NMHCs). Here, we argue that these contrasting ozone-trend profiles might be partially responsible for insignificant long-term trends in the tropical total column ozone. On seasonal scale, positive trends are observed during all the seasons in the upper troposphere while structure of trend profile varies in lower stratosphere. Seasonal variations of ozone trends and its linkages with stratospheric intrusions and increasing trends in lightning flashes in the troposphere are also discussed.

Lightning Applications in Weather and Climate Research

Thunderstorms, and lightning in particular, are a major natural hazard to the public, aviation, power companies, and wildfire managers. Lightning causes great damage and death every year but also tells us about the inner working of storms. Since lightning can be monitored from great distances from the storms themselves, lightning may allow us to provide early warnings for severe weather phenomena such as hail storms, flash floods, tornadoes, and even hurricanes. Lightning itself may impact the climate of the Earth by producing nitrogen oxides (NOx), a precursor of tropospheric ozone, which is a powerful greenhouse gas. Thunderstorms themselves influence the climate system by the redistribution of heat, moisture, and momentum in the atmosphere. What about future changes in lightning and thunderstorm activity? Many studies show that higher surface temperatures produce more lightning, but future changes will depend on what happens to the vertical temperature profile in the troposphere, as well as changes in water balance, and even aerosol loading of the atmosphere. Finally, lightning itself may provide a useful tool for tracking climate change in the future, due to the nonlinear link between lightning, temperature, upper tropospheric water vapor, and cloud cover.

Radical loss in the atmosphere from Cu-Fe redox coupling in aerosols

Abstract. The hydroperoxyl radical (HO2) is a major precursor of OH and tropospheric ozone. OH is the main atmospheric oxidant, while tropospheric ozone is an important surface pollutant and greenhouse gas. Standard gas-phase models for atmospheric chemistry tend to overestimate observed HO2 concentrations, and this has been tentatively attributed to heterogeneous uptake by aerosol particles. It is generally assumed that HO2 uptake by aerosol involves conversion to H2O2, but this is of limited efficacy as an HO2 sink because H2O2 can photolyze to regenerate OH and from there HO2. Joint atmospheric observations of HO2 and H2O2 suggest that HO2 uptake by aerosols may in fact not produce H2O2. Here we propose a catalytic mechanism involving coupling of the transition metal ions Cu(I)/Cu(II) and Fe(II)/Fe(III) to rapidly convert HO2 to H2O in aqueous aerosols. The implied HO2 uptake and conversion to H2O significantly affects global model predictions of tropospheric OH, ozone, carbon monoxide (CO) and other species, improving comparisons to observations in the GEOS-Chem model. It represents a previously unrecognized positive radiative forcing of aerosols through the effects on the chemical budgets of major greenhouse gases including methane and hydrofluorocarbons (HFCs).

The impact of biogenic volatile organic compounds emission on photochemical processes ccurring in the troposphere.

Biogenic volatile organie compounds (BVOCs) have a signifl- cant impact on air quality in the ground layer of the atmosphere and they play a major role in forming the climate. They are the main precursors of tropospheric ozone and they are a source of second- ary organie aerosols in the atmosphere. Indirectly they also aflect the climate-forming processes. The paper presents the influence of BVOCs on photochemical processes occurring in the atmosphere. The main mechanisms of reactions assodated with BVOC oxida- tion in the air and the formation of secondary organie aerosols have been discussed here. Physico-chemical conditions of the course of the indicated mechanisms have been identifled. The problems and uncertainties faced by atmospheric chemists while preparing a qualitative and quantitative description of chemical reactions in the atmosphere involving BVOCs have been discussed as well

Evaluation of two isoprene emission models for use in a long-range air pollution model

Abstract. Knowledge about isoprene emissions and concentration distribution is important for chemistry transport models (CTMs), because isoprene acts as a precursor for tropospheric ozone and subsequently affects the atmospheric concentrations of many other atmospheric compounds. Isoprene has a short lifetime, and hence it is very difficult to evaluate its emission estimates against measurements. For this reason, we coupled two isoprene emission models with the Danish Eulerian Hemispheric Model (DEHM), and evaluated the simulated background ozone concentrations based on different models for isoprene emissions. In this research, results of using the two global biogenic emission models; GEIA (Global Emissions Inventory Activity) and MEGAN (the global Model of Emissions of Gases and Aerosols from Nature) are compared and evaluated. The total annual emissions of isoprene for the year 2006 estimated by using MEGAN is 592 Tg yr−1 for an extended area of the Northern Hemisphere, which is 21% higher than that estimated by using GEIA. The overall feature of the emissions from the two models is quite similar, but differences are found mainly in Africa's savannah and in the southern part of North America. Differences in spatial distribution of emission factors are found to be a key source of these discrepancies. In spite of the short life-time of isoprene, a direct evaluation of isoprene concentrations using the two biogenic emission models in DEHM has been made against available measurements in Europe. Results show an agreement between two models simulations and the measurements in general and that the CTM is able to simulate isoprene concentrations. Additionally, investigation of ozone concentrations resulting from the two biogenic emission models show that isoprene simulated by MEGAN strongly affects the ozone production in the African savannah; the effect is up to 10% more than that obtained using GEIA. In contrast, the impact of using GEIA is higher in the Amazon region with more than 8% higher ozone concentrations compared to that of using MEGAN. Comparing the ozone concentrations obtained by DEHM using the two different isoprene models with measurements from Europe and North America, show an agreement on the hourly, mean daily and daily maximum values. However, the average of ozone daily maximum value simulated by using MEGAN is slightly closer to the measured value for the average of all measuring sites in Europe.

Pre-Harvest Sugarcane Burning: Determination of Emission Factors through Laboratory Measurements

Sugarcane is an important crop for the Brazilian economy and roughly 50% of its production is used to produce ethanol. However, the common practice of pre-harvest burning of sugarcane straw emits particulate material, greenhouse gases, and tropospheric ozone precursors to the atmosphere. Even with policies to eliminate the practice of pre-harvest sugarcane burning in the near future, there is still significant environmental damage. Thus, the generation of reliable inventories of emissions due to this activity is crucial in order to assess their environmental impact. Nevertheless, the official Brazilian emissions inventory does not presently include the contribution from pre-harvest sugarcane burning. In this context, this work aims to determine sugarcane straw burning emission factors for some trace gases and particulate material smaller than 2.5 μm in the laboratory. Excess mixing ratios for CO2, CO, NOX, UHC (unburned hydrocarbons), and PM2.5 were measured, allowing the estimation of their respective emission factors. Average estimated values for emission factors (g kg−1 of burned dry biomass) were 1,303 ± 218 for CO2, 65 ± 14 for CO, 1.5 ± 0.4 for NOX, 16 ± 6 for UHC, and 2.6 ± 1.6 for PM2.5. These emission factors can be used to generate more realistic emission inventories and therefore improve the results of air quality models.

Emission Ratios of the Tropospheric Ozone Precursors Nitrogen Dioxide and Formaldehyde from Australia’s Black Saturday Fires

The ‘Black Saturday’ fires were a series of devastating forest fires that burned across Victoria, Australia, during February and March of 2009. In this study we have used satellite data made publically available by NASA from the Ozone Monitoring Instrument (OMI) and the Atmospheric InfraRed Sounder (AIRS) to track the smoke plume from the Black Saturday firestorm and explore the chemical aging of the smoke plume in the first days after emission. We also determined emission ratios for formaldehyde and nitrogen dioxide within smoke from fires actively burning across Victoria between 7 and 17 February 2009. The mean emission ratios with respect to carbon monoxide derived for these two tropospheric ozone precursors are (0.016 ± 0.004 mol.mol−1) for formaldehyde and (0.005 ± 0.002 mol.mol−1) for nitrogen dioxide. The mean emission ratio for formaldehyde with respect to CO is in broad agreement with values previously quoted in the literature for temperate forest fires. However, to our knowledge there are no previous measurements of emission ratios for nitrogen dioxide from Australian temperate forest fires.

Economically consistent long-term scenarios for air pollutant emissions

Pollutant emissions such as aerosols and tropospheric ozone precursors substantially influence climate. While future century-scale scenarios for these emissions have become more realistic through the inclusion of emission controls, they still potentially lack consistency between surface pollutant concentrations and regional levels of affluence. We find that the default method of scenario construction, whereby emissions factors converge to similar values in different regions, does not yield pollution concentrations consistent with historical experience. We demonstrate a methodology combining use of an integrated assessment model and a three-dimensional atmospheric chemical transport model, whereby a reference scenario is constructed by requiring consistent surface pollutant concentrations as a function of regional income over the 21st century. By adjusting air pollutant emission control parameters, we improve consistency between projected PM2.5 and economic income among world regions through time; consistency for ozone is also improved but is more difficult to achieve because of the strong influence of upwind world regions. Reference case pollutant emissions described here were used to construct the RCP4.5 Representative Concentration Pathway climate policy scenario.

Comparing monoterpenoid emissions and net photosynthesis of beech (Fagus sylvatica L.) in controlled and natural conditions

Although biogenic volatile organic compounds (BVOCs) only represent a very limited fraction of the plant’s carbon (C) budget, they play an important role in atmospheric chemistry for example as a precursor of tropospheric ozone . We performed a study comparing BVOC emissions of European beech ( Fagus sylvatica L.) in controlled and natural environmental conditions. A young and adult beech tree was exposed to short-term temperature variations in growth room conditions and in an experimental forest, respectively. This study attempts to clarify how short-term temperature variations between days influenced the ratio between monoterpenoid (MT) emissions and net photosynthesis (Pn). Within a temperature range of 17–27 °C and 13–23 °C, the MT/Pn carbon ratio increased 10–30 fold for the growth room and forest, respectively. An exponential increasing trend between MT/Pn C ratio and air temperature was observed in both conditions. Beech trees re-emitted a low fraction of the assimilated C back into the atmosphere as MT: 0.01–0.12% and 0.01–0.30% with a temperature rise from 17 to 27 °C and 13–23 °C in growth room and forest conditions, respectively. However, the data showed that the MT/Pn C ratio of young and adult beech trees responded significantly to changes in temperature. ► Comparison of indoor and outdoor measurements of monoterpenoids and photosynthesis. ► Monoterpenoid/photosynthesis showed exponential relationship with air temperature. ► Young and adult beech responded similarly to the changes in air temperature.

A review of scientifc linkages and interactions between climate change and air quality, with implications for air quality management in South Africa

In recent years there has been considerable advancement in our scientifc understanding of the linkages and interactions between climate change and air quality. A warmer, evolving climate is likely to have severe consequences for air quality due to impacts on pollution sources and meteorology. Climate-induced changes to sources of tropospheric ozone precursor gases and to atmospheric circulation are likely to lead to changes in both the concentration and dispersion of near-surface ozone that could act to offset improvements in air quality. The control of air pollutants through air quality management is also likely to impact on climate change, with reductions in ozone, particulate matter and sulphur dioxide being of particular interest. The improved understanding of the relationship between air quality and climate change provides a scientific basis for policy interventions. After a review of the scientific linkages, the potential to include climate change considerations in air quality management planning processes in South Africa was examined.

Analysis of spatial-temporal variability of tropospheric NO2 column over Moscow megapolis using OMI spectrometer (Aura satellite) data

Results of analysis of nitrogen dioxide (NO2) tropo� spheric column amount over Moscow and its suburbs during the period from 2004 to 2009 are described. Spa� tial distributions of longterm mean NO 2 content and NO2 contents in opposite phases of its weekly and sea� sonal cycles are presented. The maximum annual val� ues of NO2 reaching 8.3 × 10 15 mol cm -2 were recorded east of the Moscow Ring Highway (MRH) between Balashikha and Lyubertsy, while the minimum values were recorded over Zelenograd (less than 5 × 10 15 mol cm -2 ). The peaktopeak amplitude of the weekly NO2 cycle (with a maximum on Wednesday and minimum on Sunday) is 2.7 × 10 15 mol cm -2 . The peaktopeak amplitude of the seasonal cycle (with a maximum in September and minimum in December) reaches 7.8 × 10 15 mol cm -2 . Interannual variability of NO2 is described by a statistically significant linear trend with a slope coefficient of -5.52 × 10 14 15 mol cm -2 /yr. Nitrogen oxides (NOx = NO + NO2) play a key role in the atmospheric chemistry. In the stratosphere, NOx participates in the catalytic cycle of ozone destruction and the presence of NO x in the boundary layer facilitates ozone formation in the troposphere (1). Since NOx is a precursor of tropospheric ozone, nitrate aerosol, and hydroxyl, it determines the oxidiz� ing ability of the atmosphere. The presence of NOx facilitates radiation warming of the atmosphere (2), while acid rains caused by anthropogenic emissions of NOx lead to degradation of ecosystems in water reser� voirs and forests. Combustion of fuel (predominantly automobiles, thermal power stations, and aviation), burning of bio� mass, thunderstorm discharges, soil emission includ� ing decomposition of nitrogen fertilizers, oxidizing of nitrogen oxide (N2O), and advection of NO2 from the stratosphere are sources of NOx in the troposphere. Despite the fact that the estimates of the intensity of NO2 sources are very uncertain, it is considered that not less than 50% of its tropospheric content is deter� mined by fuel combustion; i.e., it has an anthropo� genic origin (1). The tropospheric concentration of NO2 is strongly determined by local sources, and its distribution is regional. Emission of NO2 by the Moscow megapolis is the dominant source of tropospheric pollution in the Moscow region. The network of groundbased sta� tions for spectral observation of NO2 in the atmo� spheric column is scarce and does not provide for the presentation of the spatial structure of pollution in the Moscow region. Surface concentrations of NO2 in the urban conditions (observations in Moscow are pro� vided by the Mosecomonitoring unitary enterprise) are extremely variable and depend on the local pollu� tion sources, which in turn hamper the general presen� tation of pollution in the megapolis. Recently, modern satellite monitoring systems have been used more and more in the analysis of regional pollution of the tropo� sphere. They combine uniform spatial coverage of the territory with observations and sufficiently high dis� cretization of observations in time. Increased values of NO 2 concentration over megapolises cities (3) are clearly seen in the global fields of tropospheric NO2 content obtained from the observations using the GOME, SCIAMACHY, and GOME-2 instruments (the spatial resolutions of these instruments are 40 × 320, 30 × 60, and 40 × 80 km, respectively). The objec� tive of this work is analysis of regularities of the spatial distribution and time variability of the tropospheric NO2 content over Moscow using the data of the Ozone Monitoring Instrument (OMI). Its high spatial resolu� tion, in principle, allows us to distinguish the pollution details within the megapolis.