A5030430456- Atmospheric chemistry and aerosols
- Atmospheric Ozone and Climate
- Atmospheric and Environmental Gas Dynamics
- Air Quality and Health Impacts
- Air Quality Monitoring and Forecasting
- Plant responses to elevated CO2
- Vehicle emissions and performance
- Atmospheric aerosols and clouds
- Odor and Emission Control Technologies
- Soil Carbon and Nitrogen Dynamics
- Spectroscopy and Laser Applications
- Methane Hydrates and Related Phenomena
- Hydrocarbon exploration and reservoir analysis
- Environmental Justice and Health Disparities
- Climate Change and Health Impacts
- Urban Transport and Accessibility
- Impact of Light on Environment and Health
- Synthesis and characterization of novel inorganic/organometallic compounds
- Isotope Analysis in Ecology
- Marine and coastal ecosystems
- Advanced Chemical Sensor Technologies
- Water Quality Monitoring and Analysis
- Wastewater Treatment and Nitrogen Removal
- Organometallic Complex Synthesis and Catalysis
- Wind and Air Flow Studies
University of Virginia
2016-2025
Virginia Tech
2021
University of California, Berkeley
2011-2016
Berkeley College
2014-2015
Langley Research Center
2014-2015
Planetary Science Institute
2015
University of Colorado Denver
2007-2009
University of Colorado Health
2007
Laboratory studies have established a number of chemical pathways by which nitrogen oxides (NO(x)) affect atmospheric organic aerosol (OA) production. However, these effects not been directly observed in ambient OA. We report measurements particulate nitrates Bakersfield, California, the nighttime formation increases with NO(x) and is suppressed high concentrations molecules that rapidly react nitrate radical (NO(3))--evidence multigenerational chemistry responsible for This class represents...
Dry deposition of ozone is an important sink in near surface air. When dry occurs through plant stomata, can injure the plant, altering water and carbon cycling reducing crop yields. Quantifying both stomatal nonstomatal uptake accurately relevant for understanding ozone's impact on human health as air pollutant climate a potent short-lived greenhouse gas primary control removal several reactive gases pollutants. Robust estimates require knowledge relative importance individual pathways, but...
Abstract. We describe the effects of nitrogen oxide (NOx) and organic reactivity reductions on frequency high ozone days in California's San Joaquin Valley. use sixteen years observations ozone, oxides, temperature at sites upwind, within, downwind three cities to assess probability exceeding California 8-h average standard 70.4 ppb each location. The comprehensive data records region steep decreases emissions over last decade are sufficient constrain relative import NOx violations. show...
Abstract. Organic aerosol (OA) is an important fraction of submicron aerosols. However, it challenging to predict and attribute the specific organic compounds sources that lead observed OA loadings, largely due contributions from secondary production. This especially true for megacities surrounded by numerous regional create background. Here, we utilize in situ gas observations collected on board NASA DC-8 during NASA–NIER KORUS-AQ (Korea–United States Air Quality) campaign investigate...
Atmospheric photooxidation of isoprene is an important source secondary organic aerosol (SOA) and there increasing evidence that anthropogenic oxidant emissions can enhance this SOA formation. In work, we use ambient observations organosulfates formed from epoxydiols (IEPOX) methacrylic acid epoxide (MAE) a broad suite chemical measurements to investigate the relative importance nitrogen oxide (NO/NO2) hydroperoxyl (HO2) formation pathways at forested site in California. contrast IEPOX,...
Abstract. Alkyl and multifunctional organic nitrates, molecules of the chemical form RONO2, are products chain terminating reactions in tropospheric HOx NOx catalytic cycles thereby impact ozone formation locally. Many class have lifetimes that long enough they can be transported over large distances. If RONO2 then decompose to deliver remote regions affect production rates locations distant from original source. While measurements total (ΣANs) small straight alkyl nitrates routine, specific...
Abstract. The San Joaquin Valley (SJV) experiences some of the worst ozone air quality in US, frequently exceeding California 8 h standard 70.4 ppb. To improve our understanding trends number violations SJV, we analyze observed relationships between organic reactivity, nitrogen oxides (NOx), and daily maximum temperature southern SJV using measurements made as part at Nexus Air Quality Climate Change 2010 (CalNex-SJV). We find daytime speciated reactivity with respect to OH during CalNex-SJV...
The Korea-United States Air Quality Study (KORUS-AQ) took place in spring 2016 to better understand air pollution Korea. In support of KORUS-AQ, 2554 whole samples (WAS) were collected aboard the NASA DC-8 research aircraft and analyzed for 82 C1–C10 volatile organic compounds (VOCs) using multi-column gas chromatography. Together with fast-response measurements from other groups, used characterize VOC composition Seoul surrounding regions, determine which VOCs are major ozone precursors...
Ozone pollution affects human health, especially in urban areas on hot sunny days. Its basic photochemistry has been known for decades and yet it is still not possible to correctly predict the high ozone levels that are greatest threat. The CalNex_SJV study Bakersfield CA May/June 2010 provided an opportunity examine area surrounded by agriculture. measurement suite included hydroxyl (OH), hydroperoxyl (HO<sub>2</sub>), OH reactivity, which compared with output of a photochemical box model....
Abstract. Global coupled chemistry–climate models underestimate carbon monoxide (CO) in the Northern Hemisphere, exhibiting a pervasive negative bias against measurements peaking late winter and early spring. While this has been commonly attributed to underestimation of direct anthropogenic biomass burning emissions, chemical production loss via OH reaction from emissions biogenic volatile organic compounds (VOCs) play an important role. Here we investigate reasons for using aircraft taken...
Houston, Texas is a major U.S. urban and industrial area where poor air quality unevenly distributed disproportionate share located in low-income, non-white, Hispanic neighborhoods. We have traditionally lacked city-wide observations to fully describe these spatial heterogeneities Houston cities globally, especially for reactive gases like nitrogen dioxide (NO2). Here, we analyze novel high-spatial-resolution (250 m × 500 m) NO2 vertical columns measured by the NASA GCAS airborne...
The Seoul Metropolitan Area (SMA) has a population of 24 million and frequently experiences unhealthy levels ozone (O3). In this work, measurements taken during the Korea-United States Air Quality Study (KORUS-AQ, 2016) are used to explore regional gradients in O3 its chemical precursors, an observationally-constrained 0-D photochemical box model is quantify key aspects production including sensitivity precursor gases. Box performance was evaluated by comparing modeled concentrations select...
Abstract. A relaxed eddy accumulation (REA) system combined with a nitrous acid (HONO) analyzer was developed to measure atmospheric HONO vertical fluxes. The consists of three major components: (1) fast-response sonic anemometer measuring both wind velocity and air temperature, (2) controlling unit separating motions into updraft downdraft samplers by the sign velocity, (3) highly sensitive based on aqueous long path absorption photometry that measures concentrations in updrafts downdrafts....
Limitations in the chemical characterization of tropospheric organic aerosol (OA) continue to impede attempts fully understand its sources and sinks. To assess role nitrates OA, we used a new thermal dissociation‐laser induced fluorescence‐based (TD‐LIF) technique obtain high‐time‐resolution record total (hereafter ΣANs aer ) at Bakersfield, CA supersite during 2010 CalNex campaign. The TD‐LIF measurements compare well with Fourier transform infrared from collocated filter samples. These...
Abstract Measurements of HONO (g) and particulate nitrite (NO 2 − (p) ) were made with a modified Ambient Ion Monitor–Ion Chromatography (AIM‐IC) instrument during California at the Nexus Air Quality Climate 2010 in Bakersfield, CA (CalNex‐San Joaquin Valley (SJV)). Observations gas matter (PM 2.5 water‐soluble composition showed accumulation both species night, followed by loss next day. Intercomparison Stripping Coil‐UV/Vis Absorption Photometer (SC‐AP) demonstrated excellent agreement...
Abstract Coastal regions have historically represented a significant challenge for air quality investigations because of water–land boundary transition characteristics and paucity measurements available over water. Prior studies identified the formation high levels ozone water bodies, such as Chesapeake Bay, that can potentially recirculate back land to significantly impact populated areas. Earth-observing satellites forecast models face challenges in capturing coastal zone where small-scale...
Reactive nitrogen oxides (NOy; NOy = NO + NO2 HONO) decrease air quality and impact radiative forcing, yet the factors responsible for their emission from nonpoint sources (i.e., soils) remain poorly understood. We investigated that control production of aerobic in forest soils using molecular techniques, process-based assays, inhibitor experiments. subsequently used these data to identify hotspots gas emissions across forests eastern United States. Here, we show oxide soil are mediated by...
Abstract. Nitrogen oxides (NOx) have fallen steadily across the US over last 15 years. At same time, NOx concentrations decrease on weekends relative to weekdays, largely without co-occurring changes in other gas-phase emissions, due patterns of diesel truck activities. These trends taken together provide two independent constraints role nonlinear chemistry atmospheric oxidation. In this context, we interpret interannual wintertime ammonium nitrate (NH4NO3) San Joaquin Valley California, a...
Aircraft observations and ozonesonde profiles collected on July 14 27, 2011, during the Maryland month-long DISCOVER-AQ campaign, indicate presence of stratospheric air just above planetary boundary layer (PBL). This raises question whether summer intrusions (SIs) elevate surface ozone levels to what degree they influence background contribute production. We used idealized tracers, along with observations, determine frequency extent SIs in 2011. On 4 flight days, were detected layers that...
Abstract Volatile nitrogen oxides (N 2 O, NO, NO , HONO, …) can negatively impact climate, air quality, and human health. Using soils collected from temperate forests across the eastern United States, we show microbial communities involved in (N) cycling are structured, large part, by composition of overstory trees, leading to predictable N‐cycling syndromes, with consequences for emissions volatile air. Trees associating arbuscular mycorrhizal (AM) fungi promote soil higher N‐cycle...
Abstract Air pollution disproportionately burdens communities of color and lower‐income in US cities. We have generally lacked city‐wide concentration measurements that resolve the steep spatiotemporal gradients primary pollutants required to describe intra‐urban air inequality. Here, we use observations from recently launched TROPospheric Ozone Monitoring Instrument (TROPOMI) satellite sensor physics‐based oversampling nitrogen dioxide (NO 2 ) disparities with race, ethnicity, income 52...
Abstract. Glyoxal (CHOCHO), the simplest dicarbonyl in troposphere, is a potential precursor for secondary organic aerosol (SOA) and brown carbon (BrC) affecting air quality climate. The airborne measurement of CHOCHO concentrations during KORUS-AQ (KORea–US Air Quality study) campaign 2016 enables detailed quantification loss mechanisms pertaining to SOA formation real atmosphere. production this molecule was mainly from oxidation aromatics (59 %) initiated by hydroxyl radical (OH). found...
In the United States, PM2.5 and NOx pollution disproportionately burden communities of color lower income. However, such information is lacking when it comes to hazardous air pollutants (HAPs) like toxic volatile organic compounds, for which city-wide measurements are more challenging thus not available in routine observations.In this study, we use highest spatially resolved (~2 km) airborne emissions concentrations ever reported HAPs while covering a whole megacity, combine these...