A global climatological distribution of tropospheric OH is computed using observed distributions of O3, H2O, NOt (NO2 +NO + 2N2O5 + NO3 + HNO2 +HNO4), CO, hydrocarbons, temperature, and cloud optical ...depth. Global annual mean OH is 1.16×106 molecules cm−3 (integrated with respect to mass of air up to 100 hPa within ±32° latitude and up to 200 hPa outside that region). Mean hemispheric concentrations of OH are nearly equal. While global mean OH increased by 33% compared to that from Spivakovsky et al. 1990, mean loss frequencies of CH3CCl3 and CH4 increased by only 23% because a lower fraction of total OH resides in the lower troposphere in the present distribution. The value for temperature used for determining lifetimes of hydrochlorofluorocarbons (HCFCs) by scaling rate constants Prather and Spivakovsky, 1990 is revised from 277 K to 272 K. The present distribution of OH is consistent within a few percent with the current budgets of CH3CCl3 and HCFC‐22. For CH3CCl3, it results in a lifetime of 4.6 years, including stratospheric and ocean sinks with atmospheric lifetimes of 43 and 80 years, respectively. For HCFC‐22, the lifetime is 11.4 years, allowing for the stratospheric sink with an atmospheric lifetime of 229 years. Corrections suggested by observed levels of CH2Cl2 (annual means) depend strongly on the rate of interhemispheric mixing in the model. An increase in OH in the Northern Hemisphere by 20% combined with a decrease in the southern tropics by 25% is suggested if this rate is at its upper limit consistent with observations of CFCs and 85Kr. For the lower limit, observations of CH2Cl2 imply an increase in OH in the Northern Hemisphere by 35% combined with a decrease in OH in the southern tropics by 60%. However, such large corrections are inconsistent with observations for 14CO in the tropics and for the interhemispheric gradient of CH3CCl3. Industrial sources of CH2Cl2 are sufficient for balancing its budget. The available tests do not establish significant errors in OH except for a possible underestimate in winter in the northern and southern tropics by 15–20% and 10–15%, respectively, and an overestimate in southern extratropics by ∼25%. Observations of seasonal variations of CH3CCl3, CH2Cl2, 14CO, and C2H6 offer no evidence for higher levels of OH in the southern than in the northern extratropics. It is expected that in the next few years the latitudinal distribution and annual cycle of CH3CCl3 will be determined primarily by its loss frequency, allowing for additional constraints for OH on scales smaller than global.
Identifying the contributions of chemistry and transport to observed ozone pollution using regional‐to‐global models relies on accurate representation of ozone dry deposition. We use a recently ...developed configuration of the NOAA GFDL chemistry‐climate model – in which the atmosphere and land are coupled through dry deposition—to investigate the influence of ozone dry deposition on ozone pollution over northern midlatitudes. In our model, deposition pathways are tied to dynamic terrestrial processes, such as photosynthesis and water cycling through the canopy and soil. Small increases in winter deposition due to more process‐based representation of snow and deposition to surfaces reduce hemispheric‐scale ozone throughout the lower troposphere by 5–12 ppb, improving agreement with observations relative to a simulation with the standard configuration for ozone dry deposition. Declining snow cover by the end of the 21st‐century tempers the previously identified influence of rising methane on winter ozone. Dynamic dry deposition changes summer surface ozone by −4 to +7 ppb. While previous studies emphasize the importance of uptake by plant stomata, new diagnostic tracking of depositional pathways reveals a widespread impact of nonstomatal deposition on ozone pollution. Daily variability in both stomatal and nonstomatal deposition contribute to daily variability in ozone pollution. Twenty‐first century changes in summer deposition result from a balance among changes in individual pathways, reflecting differing responses to both high carbon dioxide (through plant physiology versus biomass accumulation) and water availability. Our findings highlight a need for constraints on the processes driving ozone dry deposition to test representation in regional‐to‐global models.
Economic theory often provides shape restrictions on functions of interest in applications, such as monotonicity, convexity, non-increasing (non-decreasing) returns to scale, or the Slutsky ...inequality of consumer theory; but economic theory does not provide finite-dimensional parametric models. This motivates nonparametric estimation under shape restrictions. Nonparametric estimates are often very noisy. Shape restrictions stabilize nonparametric estimates without imposing arbitrary restrictions, such as additivity or a single-index structure, that may be inconsistent with economic theory and the data. This paper explains how to estimate and obtain an asymptotic uniform confidence band for a conditional mean function under possibly nonlinear shape restrictions, such as the Slutsky inequality. The results of Monte Carlo experiments illustrate the finite-sample performance of the method, and an empirical example illustrates its use in an application.
Abstract Tropospheric ozone plays a major role in Earth’s atmospheric chemistry processes and also acts as an air pollutant and greenhouse gas. Due to its short lifetime, and dependence on sunlight ...and precursor emissions from natural and anthropogenic sources, tropospheric ozone’s abundance is highly variable in space and time on seasonal, interannual and decadal time-scales. Recent, and sometimes rapid, changes in observed ozone mixing ratios and ozone precursor emissions inspired us to produce this up-to-date overview of tropospheric ozone’s global distribution and trends. Much of the text is a synthesis of in situ and remotely sensed ozone observations reported in the peer-reviewed literature, but we also include some new and extended analyses using well-known and referenced datasets to draw connections between ozone trends and distributions in different regions of the world. In addition, we provide a brief evaluation of the accuracy of rural or remote surface ozone trends calculated by three state-of-the-science chemistry-climate models, the tools used by scientists to fill the gaps in our knowledge of global tropospheric ozone distribution and trends.
The bootstrap is a method for estimating the distribution of an estimator or test statistic by resampling one's data or a model estimated from the data. Under conditions that hold in a wide variety ...of econometric applications, the bootstrap provides approximations to distributions of statistics, coverage probabilities of confidence intervals, and rejection probabilities of hypothesis tests that are more accurate than the approximations of first-order asymptotic distribution theory. The reductions in the differences between true and nominal coverage or rejection probabilities can be very large. In addition, the bootstrap provides a way to carry out inference in certain settings where obtaining analytic distributional approximations is difficult or impossible. This article explains the usefulness and limitations of the bootstrap in contexts of interest in econometrics. The presentation is informal and expository. It provides an intuitive understanding of how the bootstrap works. Mathematical details are available in the references that are cited.
This article describes three methods for carrying out nonasymptotic inference on partially identified parameters that are solutions to a class of optimization problems. Applications in which the ...optimization problems arise include estimation under shape restrictions, estimation of models of discrete games, and estimation based on grouped data. The partially identified parameters are characterized by restrictions that involve the unknown population means of observed random variables in addition to structural parameters. Inference consists of finding confidence intervals for functions of the structural parameters. Our theory provides finite-sample lower bounds on the coverage probabilities of the confidence intervals under three sets of assumptions of increasing strength. With the moderate sample sizes found in most economics applications, the bounds become tighter as the assumptions strengthen. We discuss estimation of population parameters that the bounds depend on and contrast our methods with alternative methods for obtaining confidence intervals for partially identified parameters. The results of Monte Carlo experiments and empirical examples illustrate the usefulness of our method.
Avian bornaviral ganglioneuritis, often referred to as parrot wasting disease, is associated with a newly discovered avian virus from the taxonomic family Bornaviridae. Research regarding the ...pathogenesis and treatment for this disease is ongoing, with implications for understanding other emerging human and nonhuman diseases, as well as the health and ecology of wildlife. At this time, numerous questions remain unanswered regarding the transmission of the disease, best practices for diagnostic sampling and testing, and whether currently used drug therapies are effective or harmful for afflicted birds. The pathogenesis of the disease also remains unclear with many birds showing resistance to the effects of the virus and being able to remain clinically unaffected for years, while other birds succumb to its effects. New research findings regarding avian bornaviral ganglioneuritis are discussed and important as yet unanswered questions are identified.
In nonparametric instrumental variable estimation, the function being estimated is the solution to an integral equation. A solution may not exist if, for example, the instrument is not valid. This ...paper discusses the problem of testing the null hypothesis that a solution exists against the alternative that there is no solution. We give necessary and sufficient conditions for existence of a solution and show that uniformly consistent testing of an unrestricted null hypothesis is not possible. Uniformly consistent testing is possible, however, if the null hypothesis is restricted by assuming that any solution to the integral equation is smooth. Many functions of interest in applied econometrics, including demand functions and Engel curves, are expected to be smooth. The paper presents a statistic for testing the null hypothesis that a smooth solution exists. The test is consistent uniformly over a large class of probability distributions of the observable random variables for which the integral equation has no smooth solution. The finite-sample performance of the test is illustrated through Monte Carlo experiments.
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