Health benefits of reducing NO x emissions in the presence of epidemiological and atmospheric nonlinearities

Recent epidemiological evidence suggests that the logarithm of concentration is a better predictor of mortality risk from long-term exposure to ambient PM2.5 and NO2 than concentration itself. A log-concentration-response function (CRF) predicts a heightened excess risk per unit concentration at low levels of exposure that further increases as the air becomes less polluted. Using an adjoint air quality model, we estimate the public health benefits of reducing NO x emissions, on a per-ton and source-by-source basis. Our estimates of benefits-per-ton assume linear in concentration and log-concentration CRFs for NO2 and a CRF that is linear in concentration for O3. We apply risk coefficients estimated using the Canadian Census Health and Environment Cohort. We find that a log-concentration CRF for NO2 leads almost consistently to larger benefits-per-ton than a linear in concentration CRF (e.g., $500 000 ton-1 compared to$270 000 ton-1 for Ottawa). We observe that concentrations gradually decline due to widespread, progressive emissions abatement, entailing increasing health benefits as a result of (1) a log-concentration CRF for NO2 and (2) the nonlinear response of O3 to NO x emissions. Our results indicate that NO x abatement has the potential to incur substantial and increasing health benefits, by up to five times with 85% emission reductions, for Canada into the future

Adjoint estimation of ozone climate penalties

An adjoint of a regional chemical transport model is used to calculate location-specific temperature influences (climate penalties) on two policy-relevant ozone metrics: concentrations in polluted regions (>65 ppb) and short-term mortality in Canada and the U.S. Temperature influences through changes in chemical reaction rates, atmospheric moisture content, and biogenic emissions exhibit significant spatial variability. In particular, high-NO x, polluted regions are prominently distinguished by substantial climate penalties (up to 6.2 ppb/K in major urban areas) as a result of large temperature influences through increased biogenic emissions and nonnegative water vapor sensitivities. Temperature influences on ozone mortality, when integrated across the domain, result in 369 excess deaths/K in Canada and the U.S. over a summer season - an impact comparable to a 5% change in anthropogenic NOx emissions. As such, we suggest that NOx control can be also regarded as a climate change adaptation strategy with regard to ozone air quality. Key Points Ozone climate penalties in North America show great spatial variability High-NOx regions are among locations with the largest climate penalties NOx control can be seen as a climate change adap

Attainment vs exposure: Ozone metric responses to source-specific NO x controls using adjoint sensitivity analysis

We establish linkages between sources of NOx emissions and two types of national ozone metrics in Canada and the U.S. using the adjoint of an air quality model. We define an attainment-based metric using probabilistic design values (PDVs) exceeding 65 ppb to represent polluted regions and define an exposure-based metric as the premature mortality count related to short-term ozone exposure, both in Canada and the U.S. Our results reveal differences in both temporally averaged and day-specific influences of NOx emission controls across source locations. We find NOx emission reductions in California and the eastern U.S. to be most effective for reducing attainment- and exposure-based metrics, amounting to a total reduction of 6500 ppb in PDVs and 613 deaths/season nationally from a 10% reduction in NOx emissions from those source locations. While source controls in the remainder of the western U.S. are beneficial at reducing nonattainment, these reductions are less influential on ozone mortality. We also find that while exposure-based metrics are sensitive to daily emission reductions, much of the reduction in PDVs arises from controlling emissions on only a fraction of simulation days. We further illustrate the dependency of adjoint estimates of emission influences on the choice of averaging period as a follow-up to previous work

Variability in ozone metrics with emission reductions and its application in health impact assessment

With advancing evidence of long-term health risks of ozone exposure, cumulative exposures are of interest for air quality regulation. The current form of the ozone air quality standard in the United States pertains to an extreme value (the design value) of the ozone distribution. Using atmospheric chemical transport modeling, we examine how well attainment metrics correlate with average exposure levels. We use forward sensitivity analysis to contrast the responses of two types of ozone metrics to widespread emission reductions. One such metric is based on extreme values of the ozone distribution used for attainment designation, while the other is the seasonal average ozone concentration indicative of long-term exposure levels. We find that in locations that have high day-to-day variability in ozone concentrations, design values are more sensitive to emission reductions and are least indicative of changing exposure levels with emission reductions

Analysis of methylated humic acids from fossil fuels by size exclusion chromatography and NMR

Molecular Mass (MM) distributions in humic acids from peat and two lignites have been investigated by high performance size-exclusion chromatography (SEC) after methylation and found to be in the range approximately 300 to more than 5000, with number average NM(Mn) near 800. Values of Mn determined by SEC were in good agreement with those from vapour pressure osmotery. High field 13C NMR spectra of the methylated humic acids are extremely well resolved, and indicate that the samples are significantly different, despite their similar elemental compositions and MM distributions. © 1987