Black carbon (BC) emissions play an important role in regional climate
change in the Arctic. It is necessary to pay attention to the impact of
long-range transport from regions outside the Arctic as ...BC emissions from
local sources in the Arctic were relatively small. The task force
Hemispheric Transport of Air Pollution Phase 2 (HTAP2) set up a series of
simulation scenarios to investigate the response of BC in a given region to
different source regions. This study investigated the responses of Arctic BC
concentrations and surface temperature to 20 % anthropogenic emission
reductions from six regions in 2010 within the framework of HTAP2 based on
ensemble modeling results. Emission reductions from East Asia (EAS) had the most
(monthly contributions: 0.2–1.5 ng m−3) significant impact on the
Arctic near-surface BC concentrations, while the monthly contributions from
Europe (EUR), Middle East (MDE), North America (NAM), Russia–Belarus–Ukraine
(RBU), and South Asia (SAS) were 0.2–1.0, 0.001–0.01, 0.1–0.3, 0.1–0.7, and 0.0–0.2 ng m−3,
respectively. The responses of the vertical profiles of the Arctic BC to the
six regions were found to be different due to multiple transport pathways.
Emission reductions from NAM, RBU, EUR, and EAS mainly influenced the BC
concentrations in the low troposphere of the Arctic, while most of the BC in the
upper troposphere of the Arctic derived from SAS. The response of the Arctic
BC to emission reductions in six source regions became less significant with
the increase in the latitude. The benefit of BC emission reductions in terms
of slowing down surface warming in the Arctic was evaluated by using
absolute regional temperature change potential (ARTP). Compared to the
response of global temperature to BC emission reductions, the response of
Arctic temperature was substantially more sensitive, highlighting the need
for curbing global BC emissions.
Here we present results from an evaluation of model simulations from the International Hemispheric Transport of Air Pollution Phase II (HTAPII) and Chemistry Climate Model Initiative (CCMI) model ...inter-comparison projects against a comprehensive series of ground-based, aircraft and satellite observations of ozone mixing ratios made at various locations across India. The study focuses on the recent past (observations from 2008 to 2013, models from 2009-2010) as this is most pertinent to understanding the health impacts of ozone. To our understanding this is the most comprehensive evaluation of these models' simulations of ozone across the Indian subcontinent to date. This study highlights some significant successes and challenges that the models face in representing the oxidative chemistry of the region.
Calculating a multi-model mean, a commonly used method for ensemble averaging, assumes model independence and equal model skill. Sharing of model components amongst families of models and research ...centres, conflated by growing ensemble size, means model independence cannot be assumed and is hard to quantify.
We present a methodology to produce a weighted-model ensemble projection, accounting for model performance and model independence. Model weights are calculated by comparing model hindcasts to a selection of metrics chosen for their physical relevance to the process or phenomena of interest. This weighting methodology is applied to the Chemistry–Climate Model Initiative (CCMI) ensemble to investigate Antarctic ozone depletion and subsequent recovery. The weighted mean projects an ozone recovery to 1980 levels, by 2056 with a 95 % confidence interval (2052–2060), 4 years earlier than the most recent study. Perfect-model testing and out-of-sample testing validate the results and show a greater projective skill than a standard multi-model mean. Interestingly, the construction of a weighted mean also provides insight into model performance and dependence between the models.
This weighting methodology is robust to both model and metric choices and therefore has potential applications throughout the climate and chemistry–climate modelling communities.
The recent update on the US National Ambient Air Quality Standards (NAAQS) of the ground-level ozone (O
/ can benefit from a better understanding of its source contributions in different US regions ...during recent years. In the Hemispheric Transport of Air Pollution experiment phase 1 (HTAP1), various global models were used to determine the O
source-receptor (SR) relationships among three continents in the Northern Hemisphere in 2001. In support of the HTAP phase 2 (HTAP2) experiment that studies more recent years and involves higher-resolution global models and regional models' participation, we conduct a number of regional-scale Sulfur Transport and dEposition Model (STEM) air quality base and sensitivity simulations over North America during May-June 2010. STEM's top and lateral chemical boundary conditions were downscaled from three global chemical transport models' (i.e., GEOS-Chem, RAQMS, and ECMWF C-IFS) base and sensitivity simulations in which the East Asian (EAS) anthropogenic emissions were reduced by 20 %. The mean differences between STEM surface O
sensitivities to the emission changes and its corresponding boundary condition model's are smaller than those among its boundary condition models, in terms of the regional/period-mean (<10 %) and the spatial distributions. An additional STEM simulation was performed in which the boundary conditions were downscaled from a RAQMS (Realtime Air Quality Modeling System) simulation without EAS anthropogenic emissions. The scalability of O
sensitivities to the size of the emission perturbation is spatially varying, and the full (i.e., based on a 100% emission reduction) source contribution obtained from linearly scaling the North American mean O
sensitivities to a 20% reduction in the EAS anthropogenic emissions may be underestimated by at least 10 %. The three boundary condition models' mean O
sensitivities to the 20% EAS emission perturbations are ~8% (May-June 2010)/~11% (2010 annual) lower than those estimated by eight global models, and the multi-model ensemble estimates are higher than the HTAP1 reported 2001 conditions. GEOS-Chem sensitivities indicate that the EAS anthropogenic NO
emissions matter more than the other EAS O
precursors to the North American O
, qualitatively consistent with previous adjoint sensitivity calculations. In addition to the analyses on large spatial-temporal scales relative to the HTAP1, we also show results on subcontinental and event scales that are more relevant to the US air quality management. The EAS pollution impacts are weaker during observed O
exceedances than on all days in most US regions except over some high-terrain western US rural/remote areas. Satellite O
(TES, JPL-IASI, and AIRS) and carbon monoxide (TES and AIRS) products, along with surface measurements and model calculations, show that during certain episodes stratospheric O
intrusions and the transported EAS pollution influenced O
in the western and the eastern US differently. Free-running (i.e., without chemical data assimilation) global models underpredicted the transported background O
during these episodes, posing difficulties for STEM to accurately simulate the surface O
and its source contribution. Although we effectively improved the modeled O
by incorporating satellite O
(OMI and MLS) and evaluated the quality of the HTAP2 emission inventory with the Royal Netherlands Meteorological Institute-Ozone Monitoring Instrument (KNMI-OMI) nitrogen dioxide, using observations to evaluate and improve O
source attribution still remains to be further explored.
Constraints from ozone (O3) observations over oceans
are needed in addition to those from terrestrial regions to fully understand
global tropospheric chemistry and its impact on the climate. Here, we
...provide a large data set of ozone and carbon monoxide (CO) levels observed
(for 11 666 and 10 681 h, respectively) over oceans. The data set is derived
from observations made during 24 research cruise legs of R/V Mirai during 2012 to
2017, in the Southern, Indian, Pacific, and Arctic oceans, covering the
region from 67∘ S to 75∘ N. The data are suitable for
critical evaluation of the over-ocean distribution of ozone derived from
global atmospheric chemistry models. We first give an overview of the
statistics in the data set and highlight key features in terms of
geographical distribution and air mass type. We then use the data set to
evaluate ozone mixing ratio fields from the tropospheric chemistry
reanalysis version 2 (TCR-2), produced by assimilating a suite of satellite
observations of multiple species into a global atmospheric chemistry model,
namely CHASER. For long-range transport of polluted air masses from
continents to the oceans, during which the effects of forest fires and
fossil fuel combustion were recognized, TCR-2 gave an excellent performance
in reproducing the observed temporal variations and photochemical buildup of
O3 when assessed from ΔO3∕ΔCO ratios. For clean
marine conditions with low and stable CO mixing ratios, two focused analyses
were performed. The first was in the Arctic (> 70∘ N)
in September every year from 2013 to 2016; TCR-2 underpredicted O3
levels by 6.7 ppbv (21 %) on average. The observed vertical profiles from
O3 soundings from R/V Mirai during September 2014 had less steep vertical
gradients at low altitudes (> 850 hPa) than those obtained by
TCR-2. This suggests the possibility of a more efficient descent of the
O3-rich air from above than assumed in the models. For TCR-2 (CHASER),
dry deposition on the Arctic ocean surface might also have been
overestimated. In the second analysis, over the western Pacific equatorial
region (125–165∘ E, 10∘ S to 25∘ N), the
observed O3 level more frequently decreased to less than 10 ppbv in
comparison to that obtained with TCR-2 and also those obtained in most of
the Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP)
model runs for the decade from 2000. These results imply loss processes that
are unaccounted for in the models. We found that the model's positive bias
positively correlated with the daytime residence times of air masses over a
particular grid, namely 165–180∘ E and 15–30∘ N; an
additional loss rate of 0.25 ppbv h−1 in the grid best explained the
gap. Halogen chemistry, which is commonly omitted from currently used
models, might be active in this region and could have contributed to
additional losses. Our open data set covering wide ocean regions is
complementary to the Tropospheric Ozone Assessment Report data set, which
basically comprises ground-based observations and enables a fully global
study of the behavior of O3.
Lightning can cause natural hazards that result in human and animal injuries and fatalities, infrastructure destruction, and wildfire ignition. Lightning-produced NOx (LNOx), a major NOx (NOx=NO+NO2) ...source, plays a vital role in atmospheric chemistry and global climate. The Earth has experienced marked global warming and changes in aerosol and aerosol precursor emissions (AeroPEs) since the 1960s. Investigating long-term historical (1960–2014) lightning and LNOx trends can provide important indicators for all lightning-related phenomena and for LNOx effects on atmospheric chemistry and global climate. Understanding how global warming and changes in AeroPEs influence historical lightning and LNOx trends can be helpful in providing a scientific basis for assessing future lightning and LNOx trends. Moreover, global lightning activities' responses to large volcanic eruptions such as the 1991 Pinatubo eruption are not well elucidated and are worth exploring. This study employed the widely used cloud top height lightning scheme (CTH scheme) and the newly developed ice-based ECMWF-McCAUL lightning scheme to investigate historical (1960–2014) lightning and LNOx trends and variations as well as their influencing factors (global warming, increases in AeroPEs, and the Pinatubo eruption) in the framework of the CHASER (MIROC) chemistry–climate model. The results of the sensitivity experiments indicate that both lightning schemes simulated almost flat global mean lightning flash rate anomaly trends during 1960–2014 in CHASER (the Mann–Kendall trend test (significance inferred as 5 %) shows no trend for the ECMWF-McCAUL scheme, but a 0.03 % yr−1 significant increasing trend is detected for the CTH scheme). Moreover, both lightning schemes suggest that past global warming enhances historical trends for global mean lightning density and global LNOx emissions in a positive direction (around 0.03 % yr−1 or 3 % K−1). However, past increases in AeroPEs exert an opposite effect on the lightning and LNOx trends (−0.07 % to −0.04 % yr−1 for lightning and −0.08 % to −0.03 % yr−1 for LNOx) when one considers only the aerosol radiative effects in the cumulus convection scheme. Additionally, effects of past global warming and increases in AeroPEs in lightning trends were found to be heterogeneous across different regions when analyzing lightning trends on the global map. Lastly, this paper is the first of study results suggesting that global lightning activities were markedly suppressed during the first year after the Pinatubo eruption as shown in both lightning schemes (global lightning activities decreased by as much as 18.10 % as simulated by the ECMWF-McCAUL scheme). Based on the simulated suppressed lightning activities after the Pinatubo eruption, the findings also indicate that global LNOx emissions decreased after the 2- to 3-year Pinatubo eruption (1.99 %–8.47 % for the annual percentage reduction). Model intercomparisons of lightning flash rate trends and variations between our study (CHASER) and other Coupled Model Intercomparison Project Phase 6 (CMIP6) models indicate great uncertainties in historical (1960–2014) global lightning trend simulations. Such uncertainties must be investigated further.
Lightning can cause natural hazards that result in human and animal injuries and fatalities, infrastructure destruction, and wildfire ignition. Lightning-produced NO.sub.x (LNO.sub.x ), a major ...NO.sub.x (NOx=NO+NO2) source, plays a vital role in atmospheric chemistry and global climate. The Earth has experienced marked global warming and changes in aerosol and aerosol precursor emissions (AeroPEs) since the 1960s. Investigating long-term historical (1960-2014) lightning and LNO.sub.x trends can provide important indicators for all lightning-related phenomena and for LNO.sub.x effects on atmospheric chemistry and global climate. Understanding how global warming and changes in AeroPEs influence historical lightning and LNO.sub.x trends can be helpful in providing a scientific basis for assessing future lightning and LNO.sub.x trends. Moreover, global lightning activities' responses to large volcanic eruptions such as the 1991 Pinatubo eruption are not well elucidated and are worth exploring. This study employed the widely used cloud top height lightning scheme (CTH scheme) and the newly developed ice-based ECMWF-McCAUL lightning scheme to investigate historical (1960-2014) lightning and LNO.sub.x trends and variations as well as their influencing factors (global warming, increases in AeroPEs, and the Pinatubo eruption) in the framework of the CHASER (MIROC) chemistry-climate model. The results of the sensitivity experiments indicate that both lightning schemes simulated almost flat global mean lightning flash rate anomaly trends during 1960-2014 in CHASER (the Mann-Kendall trend test (significance inferred as 5 %) shows no trend for the ECMWF-McCAUL scheme, but a 0.03 % yr.sup.-1 significant increasing trend is detected for the CTH scheme). Moreover, both lightning schemes suggest that past global warming enhances historical trends for global mean lightning density and global LNO.sub.x emissions in a positive direction (around 0.03 % yr.sup.-1 or 3 % K.sup.-1). However, past increases in AeroPEs exert an opposite effect on the lightning and LNO.sub.x trends (-0.07 % to -0.04 % yr.sup.-1 for lightning and -0.08 % to -0.03 % yr.sup.-1 for LNO.sub.x) when one considers only the aerosol radiative effects in the cumulus convection scheme. Additionally, effects of past global warming and increases in AeroPEs in lightning trends were found to be heterogeneous across different regions when analyzing lightning trends on the global map. Lastly, this paper is the first of study results suggesting that global lightning activities were markedly suppressed during the first year after the Pinatubo eruption as shown in both lightning schemes (global lightning activities decreased by as much as 18.10 % as simulated by the ECMWF-McCAUL scheme). Based on the simulated suppressed lightning activities after the Pinatubo eruption, the findings also indicate that global LNO.sub.x emissions decreased after the 2- to 3-year Pinatubo eruption (1.99 %-8.47 % for the annual percentage reduction). Model intercomparisons of lightning flash rate trends and variations between our study (CHASER) and other Coupled Model Intercomparison Project Phase 6 (CMIP6) models indicate great uncertainties in historical (1960-2014) global lightning trend simulations. Such uncertainties must be investigated further.
Ground-based remote sensing using multi-axis differential optical absorption spectroscopy (MAX-DOAS) was used to conduct continuous simultaneous observations of ozone (O
3
), nitrogen dioxide (NO
2
...), and formaldehyde (HCHO) concentrations at Chiba (35.63° N, 140.10° E, 21 m a.s.l.) and Tsukuba (36.06° N, 140.13° E, 35 m a.s.l.), Japan, for 7 years from 2013 to 2019. These are urban and suburban sites, respectively, in the greater Tokyo metropolitan area. NO
2
and HCHO are considered to be proxies for nitrogen oxides (NOx) and volatile organic compounds (VOCs), respectively, both of which are major precursors of tropospheric O
3
. The mean concentrations below an altitude of 1 km were analyzed as planetary boundary layer (PBL) concentrations. For a more spatially representative analysis around the urban area of Chiba, four MAX-DOAS instruments directed at four different azimuth directions (north, east, west, and south) were operated simultaneously and their data were unified. During the 7-year period, the satellite observations indicated an abrupt decrease in the tropospheric NO
2
concentration over East Asia, including China. This suggested that the transboundary transport of O
3
originating from the Asian continent was likely suppressed or almost unchanged during the period. Over this time period, the MAX-DOAS observations revealed the presence of almost-constant annual variations in the PBL O
3
concentration, whereas reductions in NO
2
and HCHO concentrations occurred at rates of approximately 6–10%/year at Chiba. These changes provided clear observational evidence that a decreasing NOx concentration significantly reduced the amount of O
3
quenched through NO titration under VOC-limited conditions in the urban area. Under the dominant VOC-limited conditions, the MAX-DOAS-derived concentration ratio of HCHO/NO
2
was found to be below unity in all months. Thus, the multi-component observations from MAX-DOAS provided a unique data set of O
3
, NO
2
, and HCHO concentrations for analyzing PBL O
3
variations.
We evaluate global tropospheric nitrogen dioxide (NO2) simulations
using the CHASER V4.0 global chemical transport model (CTM) at horizontal
resolutions of 0.56, 1.1, and 2.8∘. Model evaluation was ...conducted
using satellite tropospheric NO2 retrievals from the Ozone Monitoring
Instrument (OMI) and the Global Ozone Monitoring Experiment-2 (GOME-2) and
aircraft observations from the 2014 Front Range Air Pollution and
Photochemistry Experiment (FRAPPÉ). Agreement against satellite retrievals
improved greatly at 1.1 and 0.56∘ resolutions (compared to
2.8∘ resolution) over polluted and biomass burning regions. The
1.1∘ simulation generally captured the regional distribution of the
tropospheric NO2 column well, whereas 0.56∘ resolution was
necessary to improve the model performance over areas with strong local
sources, with mean bias reductions of 67 % over Beijing and 73 % over
San Francisco in summer. Validation using aircraft observations indicated
that high-resolution simulations reduced negative NO2 biases below
700 hPa over the Denver metropolitan area. These improvements in
high-resolution simulations were attributable to (1) closer spatial
representativeness between simulations and observations and (2) better
representation of large-scale concentration fields (i.e., at 2.8∘)
through the consideration of small-scale processes. Model evaluations
conducted at 0.5 and 2.8∘ bin grids indicated that the contributions
of both these processes were comparable over most polluted regions, whereas
the latter effect (2) made a larger contribution over eastern China and
biomass burning areas. The evaluations presented in this paper demonstrate
the potential of using a high-resolution global CTM for studying
megacity-scale air pollutants across the entire globe, potentially also
contributing to global satellite retrievals and chemical data assimilation.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The co-occurrence of heat waves and pollution events and the resulting high
mortality rates emphasize the importance of the co-occurrence of pollution
and temperature extremes. Through the use of ...extreme value theory and other
statistical methods, tropospheric surface ozone and temperature extremes and
their joint occurrence are analyzed over the United States during the summer
months (JJA) using measurements and simulations of the present and future
climate and chemistry. Five simulations from the Chemistry-Climate Model
Initiative (CCMI) reference experiment using specified dynamics (REFC1SD)
were analyzed: the CESM1 CAM4-chem, CHASER, CMAM, MOCAGE and MRI-ESM1r1
simulations. In addition, a 25-year present-day simulation branched off the
CCMI REFC2 simulation in the year 2000 and a 25-year future simulation
branched off the CCMI REFC2 simulation in 2100 were analyzed using CESM1
CAM4-chem. The last two simulations differed in their concentration of carbon
dioxide (representative of the years 2000 and 2100) but were otherwise
identical. In general, regions with relatively high ozone extremes over the
US do not occur in regions of relatively high temperature extremes. A new
metric, the spectral density, is developed to measure the joint extremal
dependence of ozone and temperature by evaluating the spectral dependence of
their extremes. While in many areas of the country ozone and temperature are
highly correlated overall, the correlation is significantly reduced when
examined on the higher end of the distributions. Measures of spectral density
are less than about 0.35 everywhere, suggesting that at most only about a
third of the time do extreme temperatures coincide with extreme ozone. Two
regions of the US have the strongest measured extreme dependence of ozone and
temperature: the northeast and the southeast. The simulated future increase
in temperature and ozone is primarily due to a shift in their distributions,
not to an increase in their extremes. The locations where the right-hand side
of the temperature distribution does increase (by up to 30 %) are
consistent with locations where soil–moisture feedback may be expected.
Future changes in the right-hand side of the ozone distribution range
regionally between +20 % and −10 %. The location of future increases
in the high-end tail of the ozone distribution are weakly related to those of
temperature with a correlation of 0.3. However, the regions where the
temperature extremes increase are not located where the extremes in ozone are
large, suggesting a muted ozone response.
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