Viral Shah

Viral Shah
Harvard University | Harvard · Area of Environmental Science and Engineering

PhD

About

47
Publications
12,664
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Introduction

Publications

Publications (47)
Preprint
Full-text available
Satellite-based retrievals of tropospheric NO2 columns are used to infer NOx (NO+NO2) emissions at the surface. These retrievals rely on model information for the vertical distribution of NO2. The free tropospheric background above 2 km is particularly important because the sensitivity of the retrievals increases with altitude. Free tropospheric NO...
Preprint
Air quality network data in China and South Korea show very high year-round mass concentrations of coarse particulate matter (PM) between 2.5 $\mu$m and 10 $\mu$m aerodynamic diameter, as inferred by the difference between PM10 and PM2.5 observations. This coarse PM averages 47 $\mu$g m$^{-3}$ in the North China Plain (NCP) region in 2015-2019 and...
Article
Full-text available
We present a new chemical mechanism for Hg⁰/HgI/HgII atmospheric cycling, including recent laboratory and computational data, and implement it in the GEOS-Chem global atmospheric chemistry model for comparison to observations. Our mechanism includes the oxidation of Hg⁰ by Br and OH, subsequent oxidation of HgI by ozone and radicals, respeciation o...
Article
Full-text available
Ambient fine particulate matter (PM2.5) is the world’s leading environmental health risk factor. Reducing the PM2.5 disease burden requires specific strategies that target dominant sources across multiple spatial scales. We provide a contemporary and comprehensive evaluation of sector- and fuel-specific contributions to this disease burden across 2...
Article
Full-text available
The concentration of fine particulate matter (PM2.5) across China has decreased by 30–50% over the period 2013–2018 due to stringent emission controls. However, the nitrate component of PM2.5 has not responded effectively to decreasing emissions of nitrogen oxides and has actually increased during winter haze pollution events in the North China Pla...
Article
Full-text available
Satellite nitrogen dioxide (NO2) measurements are used extensively to infer nitrogen oxide emissions and their trends, but interpretation can be complicated by background contributions to the NO2 column sensed from space. We use the step decrease of US anthropogenic emissions from the COVID-19 shutdown to compare the responses of NO2 concentrations...
Article
Full-text available
Formaldehyde (HCHO) is generated from direct urban emission sources and secondary production from the photochemical reactions of urban smog. HCHO is linked to tropospheric ozone formation, and contributes to the photochemical reactions of other components of urban smog. In this study, pollution plume intercepts during the Wintertime INvestigation o...
Article
Full-text available
Cloud water acidity affects the atmospheric chemistry of sulfate and organic aerosol formation, halogen radical cycling, and trace metal speciation. Precipitation acidity including post-depositional inputs adversely affects soil and freshwater ecosystems. Here, we use the GEOS-Chem model of atmospheric chemistry to simulate the global distributions...
Preprint
Full-text available
Cloudwater acidity affects the atmospheric chemistry of sulfate and organic aerosol formation, halogen radical cycling, and trace metal speciation. Rainwater acidity including post-depositional inputs adversely affects soil and freshwater ecosystems. Here we use the GEOS-Chem model of atmospheric chemistry to simulate the global distributions of cl...
Article
Full-text available
Satellite observations of tropospheric NO2 columns are extensively used to infer trends in anthropogenic emissions of nitrogen oxides (NOx≡NO+NO2), but this may be complicated by trends in NOx lifetime. Here we use 2004–2018 observations from the Ozone Monitoring Instrument (OMI) satellite-based instrument (QA4ECV and POMINO v2 retrievals) to exami...
Article
Full-text available
Plain Language Summary During summer, rapid transformations of primary pollutants, those emitted directly into the atmosphere, into secondary pollutants, such as particulate matter and ozone, are driven by reactions with the hydroxyl radical, formed in the atmosphere when sunlight strikes ozone in the presence of water vapor. During winter, when th...
Article
Full-text available
Fine particulate matter (PM2.5) decreased by 30–40% across China during 2013–2017 in response to the governmental Clean Air Action. However, surface ozone pollution worsened over the same period. Model simulations have suggested that the increase in ozone could be driven by the decrease in PM2.5, because PM2.5 scavenges hydroperoxy (HO2) and NOx ra...
Preprint
Full-text available
Satellite observations of tropospheric NO2 columns are extensively used to infer trends in anthropogenic emissions of nitrogen oxides (NOx ≡ NO + NO2), but this may be complicated by trends in NOx lifetime. Here we use 2004–2018 observations from the OMI satellite-based instrument (QA4ECV and POMINO v2 retrievals) to examine the seasonality and tre...
Article
Full-text available
Sulfur dioxide (SO2) is emitted in large quantities from coal‐burning power plants and leads to various harmful health and environmental effects. In this study, we use plume intercepts from the Wintertime INvestigation of Transport, Emission and Reactivity (WINTER) campaign to estimate the oxidation rates of SO2 under wintertime conditions and the...
Article
Full-text available
We present a new method for simulating heterogeneous (surface and multiphase) cloud chemistry in atmospheric models that do not spatially resolve clouds. The method accounts for cloud entrainment within the chemical rate expression, making it more accurate and stable than other approaches. Using this “entrainment-limited uptake,” we evaluate the ro...
Article
Full-text available
Air quality models have not been able to reproduce the magnitude of the observed concentrations of fine particulate matter (PM2.5) during wintertime Chinese haze events. The discrepancy has been at least partly attributed to low biases in modeled sulfate production rates, due to the lack of heterogeneous sulfate production on aerosols in the models...
Article
Full-text available
Secondary organic aerosol (SOA) from pollution sources is thought to be a minor component of organic aerosol (OA) and fine particulate matter beyond the urban scale. Here we present airborne observations of OA in the northeastern United States, showing that 58% of OA over the region during winter is secondary and originates from pollution sources....
Article
Full-text available
As part of the WINTER (Wintertime Investigation of Transport, Emissions, and Reactivity) campaign, a Particle-into-Liquid Sampler with a fraction collector was flown aboard the National Center for Atmospheric Research C-130 aircraft. Two-minute integrated liquid samples containing dissolved fine particulate matter (PM1) species were collected and a...
Article
Full-text available
Air quality models have not been able to reproduce the magnitude of the observed concentrations of fine particulate matter (PM2.5) during wintertime Chinese haze events. The discrepancy has been at least partly attributed to low biases in modeled sulfate production rates due to the lack of heterogeneous sulfate production on aerosols in the models....
Article
Full-text available
Nitrogen oxides (NOx≡NO+NO2) in the upper troposphere (UT) have a large impact on global tropospheric ozone and OH (the main atmospheric oxidant). New cloud-sliced observations of UT NO2 at 450–280 hPa (∼6–9 km) from the Ozone Monitoring Instrument (OMI) produced by NASA and the Royal Netherlands Meteorological Institute (KNMI) provide global cover...
Article
Full-text available
Sea salt aerosols (SSA) produced on sea ice surfaces by blowing snow events or the lifting of frost flower crystals have been suggested as important sources of SSA during winter over polar regions. The magnitude and relative contribution of blowing snow and frost flower SSA sources, however, remain uncertain. In this study, we use 2007–2009 aerosol...
Article
The formation of photolabile chlorine reservoirs depend on how much chloride is available in the particle to react, which requires the chlorine partitioning to the particle in the troposphere to be well understood. However, limited measurements of gas and particle composition necessary to constrain this chemistry exist. We present measurements from...
Article
We examine the distribution and fate of nitrogen oxides (NOx) in the lower troposphere over the Northeast United States (NE US) using aircraft observations from the Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) campaign in February–March 2015, as well as the GEOS-Chem chemical transport model and concurrent ground-based...
Article
We present airborne observations of gaseous reactive halogen species (HCl, Cl2, ClNO2, Br2, BrNO2, and BrCl), sulfur dioxide (SO2), and nonrefractory fine particulate chloride (pCl) and sulfate (pSO4) in power plant exhaust. Measurements were conducted during the Wintertime INvestigation of Transport, Emissions, and Reactivity campaign in February–...
Article
Sulfate (SO42-) and nitrate (NO3-) account for half of the fine particulate matter mass over the eastern United States. Their wintertime concentrations have changed little in the past decade despite considerable precursor emissions reductions. The reasons for this have remained unclear because detailed observations to constrain the wintertime gas–p...
Article
Most intensive field studies investigating aerosols have been conducted in summer, and thus, wintertime aerosol sources and chemistry are comparatively poorly understood. An aerosol mass spectrometer was flown on the National Science Foundation/National Center for Atmospheric Research C-130 during the Wintertime INvestigation of Transport, Emission...
Article
Full-text available
Nitrogen oxides (NOx ≡ NO + NO2) in the upper troposphere (UT) have a large impact on global tropospheric ozone and OH (the main atmospheric oxidant). New cloud-sliced observations of UT NO2 at 450–280 hPa (~ 6–9 km) from the OMI satellite instrument produced by NASA and KNMI provide global coverage to test our understanding of the factors controll...
Article
Full-text available
Sea salt aerosols (SSA) produced on sea ice surfaces by blowing snow events or lifting of frost flower crystals have been suggested as important sources of SSA during winter over polar regions. The magnitude and relative contribution of blowing snow and frost flower SSA sources, however, remain uncertain. In this study, we use 2007–2009 aerosol ext...
Article
Nocturnal dinitrogen pentoxide (N2O5) heterogeneous chemistry impacts regional air quality and the distribution and lifetime of tropospheric oxidants. Formed from the oxidation of nitrogen oxides, N2O5 is heterogeneously lost to aerosol with a highly variable reaction probability, γ(N2O5), dependent on aerosol composition and ambient conditions. Re...
Article
Full-text available
The Southeast Atmosphere Studies (SAS), which included the Southern Oxidant and Aerosol Study (SOAS); the Southeast Nexus (SENEX) study; and the Nitrogen, Oxidants, Mercury and Aerosols: Distributions, Sources and Sinks (NOMADSS) study, was deployed in the field from 1 June to 15 July 2013 in the central and eastern United States, and it overlapped...
Article
Full-text available
Oxidized mercury (Hg(II)) is chemically produced in the atmosphere by oxidation of elemental mercury and is directly emitted by anthropogenic activities. We use the GEOS-Chem global chemical transport model with gaseous oxidation driven by Br atoms to quantify how surface deposition of Hg(II) is influenced by Hg(II) production at different atmosphe...
Article
Sulfur and reactive bromine (Bry) play important roles in tropospheric chemistry and the global radiation budget. The oxidation of dissolved SO2 (S(IV)) by HOBr increases sulfate aerosol abundance and may also impact the Bry budget, but is generally not included in global climate and chemistry models. In this study, we implement HOBr + S(IV) reacti...
Article
Formaldehyde (HCHO) is the most important carcinogen in outdoor air among the 187 hazardous air pollutants (HAPs) identified by the US Environmental Protection Agency (EPA), not including ozone and particulate matter. However, surface observations of HCHO are sparse and the EPA monitoring network could be prone to positive interferences. Here we us...
Article
Full-text available
Oxidized mercury (Hg(II)) is chemically produced in the atmosphere by oxidation of elemental mercury and is directly emitted by anthropogenic activities. We use the GEOS-Chem global chemical transport model, with gaseous oxidation driven by Br atoms, to quantify how surface deposition of Hg(II) is influenced by Hg(II) production at different atmosp...
Article
Full-text available
Abstract Atmosphere–surface exchange of mercury, although a critical component of its global cycle, is currently poorly constrained. Here we use the GEOS-Chem chemical transport model to interpret atmospheric Hg0 (gaseous elemental mercury) data collected during the 2013 summer Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sink...
Article
Full-text available
We collected mercury observations as part of the Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) aircraft campaign over the southeastern US between 1 June and 15 July 2013. We use the GEOS-Chem chemical transport model to interpret these observations and place new constraints on bromine radical initiated mercury...
Article
Full-text available
Mercury is a global toxin that can be introduced to ecosystems through atmospheric deposition. Mercury oxidation is thought to occur in the free troposphere by bromine radicals, but direct observational evidence for this process is currently unavailable. During the 2013 Nitrogen, Oxidants, Mercury and Aerosol Distributions, Sources and Sinks (NOMAD...
Article
Full-text available
We collected mercury observations as part of the Nitrogen, Oxidants, Mercury, and Aerosol Distributions, Sources, and Sinks (NOMADSS) aircraft campaign over the southeastern US between 1 June and 15 July 2013. We use the GEOS-Chem chemical transport model to interpret these observations and place new constraints on bromine radical initiated mercury...
Conference Paper
Full-text available
The NOMADSS experiment (Nitrogen, Oxidants, Mercury and Aerosols: Deposition, Sources and Sinks) was carried out using the NSF/NCAR C-130 research aircraft during June and July, 2013. The aircraft was outfitted with an extensive suite of instrumentation for mercury (Hg), ozone (O3), nitrogen oxides (NO NO2), hydrogen oxide radicals (HOx = OH HO2),...
Article
Background, aim, and scope Traditional life cycle impact assessment methodologies have used aggregated characterization factors, neglecting spatial and temporal variations in regional impacts like photochemical oxidant formation. This increases the uncertainty of the LCA results and diminishes the ease of decision-making. This study compares four c...
Data
Supporting Information
Article
Heating and cooling systems consume the most energy and are the largest source of emissions in the entire life cycle of a house. This study compares the life cycle impacts of three residential heating and cooling systems—warm-air furnace and air-conditioner, hot water boiler and air-conditioner, and air–air heat pump over a 35-year study period. Si...

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