More Like this

1. Examining the competing effects of contemporary land management vs. land cover changes on global air quality

   https://doi.org/10.5194/acp-21-16479-2021  

   Wong, Anthony Y. ; Geddes, Jeffrey A. ( January 2021 , Atmospheric Chemistry and Physics)

   Abstract. Our work explores the impact of two important dimensions of landsystem changes, land use and land cover change (LULCC) as well as directagricultural reactive nitrogen (Nr) emissions from soils, on ozone(O3) and fine particulate matter (PM2.5) in terms of air quality overcontemporary (1992 to 2014) timescales. We account for LULCC andagricultural Nr emissions changes with consistent remote sensingproducts and new global emission inventories respectively estimating theirimpacts on global surface O3 and PM2.5 concentrations as well as Nrdeposition using the GEOS-Chem global chemical transport model. Over thistime period, our model results show that agricultural Nr emissionchanges cause a reduction of annual mean PM2.5 levels over Europe andnorthern Asia (up to −2.1 µg m−3) while increasing PM2.5 levels in India, China and the eastern US (up to +3.5 µg m−3). Land cover changes induce small reductions in PM2.5 (up to −0.7 µg m−3) over Amazonia, China and India due to reduced biogenic volatile organic compound (BVOC) emissions and enhanced deposition of aerosol precursor gases (e.g., NO2, SO2). Agricultural Nr emissionchanges only lead to minor changes (up to ±0.6 ppbv) in annual meansurface O3 levels, mainly over China, India and Myanmar. Meanwhile, ourmodel result suggests a stronger impact of LULCC on surface O3 over the time period across Southmore »America; the combination of changes in drydeposition and isoprene emissions results in −0.8 to +1.2 ppbv surfaceozone changes. The enhancement of dry deposition reduces the surface ozone level (up to −1 ppbv) over southern China, the eastern US and central Africa. The enhancement of soil NO emission due to crop expansion also contributes to surface ozone changes (up to +0.6 ppbv) over sub-Saharan Africa. Incertain regions, the combined effects of LULCC and agricultural Nr emission changes on O3 and PM2.5 air quality can be comparable (>20 %) to anthropogenic emission changes over the same time period. Finally, we calculate that the increase in global agricultural Nr emissions leads to a net increase in global land area (+3.67×106km2) that potentially faces exceedance of the critical Nr load (>5 kg N ha−1 yr−1). Our result demonstrates the impacts of contemporary LULCC and agricultural Nr emission changes on PM2.5 and O3 in terms of air quality, as well as the importanceof land system changes for air quality over multidecadal timescales.« less
2. Secondary Organic Aerosol Formation via Multiphase Reaction of Hydrocarbons in Urban Atmosphere Using the CAMx Model Integrated with the UNIPAR model

   https://doi.org/10.5194/acp-2021-1002  

   Yu, Z. ; Jang, M. ; Kim, S. ; Son, K. ; Madhu, A. ; Han, S. ; Park, J. ( January 2022 , Atmospheric chemistry and physics)

   The prediction of Secondary Organic Aerosol (SOA) in regional scales is traditionally performed by using gas-particle partitioning models. In the presence of inorganic salted wet aerosols, aqueous reactions of semivolatile organic compounds can also significantly contribute to SOA formation. The UNIfied Partitioning-Aerosol phase Reaction (UNIPAR) model utilizes the explicit gas mechanism to better predict SOA formation from multiphase reactions of hydrocarbons. In this work, the UNIPAR model was incorporated with the Comprehensive Air Quality Model with Extensions (CAMx) to predict the ambient concentration of organic matter (OM) in urban atmospheres during the Korean-United States Air Quality (2016 KORUS-AQ) campaign. The SOA mass predicted with the CAMx-UNIPAR model changed with varying levels of humidity and emissions and in turn, has the potential to improve the accuracy of OM simulations. The CAMx-UNIPAR model significantly improved the simulation of SOA formation under the wet condition, which often occurred during the KORUS-AQ campaign, through the consideration of aqueous reactions of reactive organic species and gas-aqueous partitioning. The contribution of aromatic SOA to total OM was significant during the low-level transport/haze period (24-31 May 2016) because aromatic oxygenated products are hydrophilic and reactive in aqueous aerosols. The OM mass predicted with the CAMx-UNIPAR model wasmore »compared with that predicted with the CAMx model integrated with the conventional two product model (SOAP). Based on estimated statistical parameters to predict OM mass, the performance of CAMx-UNIPAR was noticeably better than the conventional CAMx model although both SOA models underestimated OM compared to observed values, possibly due to missing precursor hydrocarbons such as sesquiterpenes, alkanes, and intermediate VOCs. The CAMx-UNIPAR model simulation suggested that in the urban areas of South Korea, terpene and anthropogenic emissions significantly contribute to SOA formation while isoprene SOA minimally impacts SOA formation.« less
3. Nitrate radicals and biogenic volatile organic compounds: oxidation, mechanisms, and organic aerosol

   https://doi.org/10.5194/acp-17-2103-2017  

   Ng, Nga Lee ; Brown, Steven S. ; Archibald, Alexander T. ; Atlas, Elliot ; Cohen, Ronald C. ; Crowley, John N. ; Day, Douglas A. ; Donahue, Neil M. ; Fry, Juliane L. ; Fuchs, Hendrik ; et al ( January 2017 , Atmospheric Chemistry and Physics)

   Abstract. Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO₃) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO₃-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO₃-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO₃ radical, the difficulty of characterizing the spatial distributions of BVOC and NO₃ within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry–climate models.
   
   This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the currentmore »literature on NO₃-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO₃-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.

   « less
4. Comparison of secondary organic aerosol generated from the oxidation of laboratory precursors by hydroxyl radicals, chlorine atoms, and bromine atoms in an oxidation flow reactor

   https://doi.org/10.1039/D2EA00018K  

   Lambe, Andrew T. ; Avery, Anita M. ; Bhattacharyya, Nirvan ; Wang, Dongyu S. ; Modi, Mrinali ; Masoud, Catherine G. ; Ruiz, Lea Hildebrandt ; Brune, William H. ( July 2022 , Environmental Science: Atmospheres)

   The role of hydroxyl radicals (OH) as a daytime oxidant is well established on a global scale. In specific source regions, such as the marine boundary layer and polluted coastal cities, other daytime oxidants, such as chlorine atoms (Cl) and even bromine atoms (Br), may compete with OH for the oxidation of volatile organic compounds (VOCs) and/or enhance the overall oxidation capacity of the atmosphere. However, the number of studies investigating halogen-initiated secondary organic aerosol (SOA) formation is extremely limited, resulting in large uncertainties in these oxidative aging processes. Here, we characterized the chemical composition and yield of laboratory SOA generated in an oxidation flow reactor (OFR) from the OH and Cl oxidation of n -dodecane ( n -C 12 ) and toluene, and the OH, Cl, and Br oxidation of isoprene and α-pinene. In the OFR, precursors were oxidized using integrated OH, Cl, and Br exposures ranging from 3.1 × 10 10 to 2.3 × 10 12 , 6.1 × 10 9 to 1.3× 10 12 and 3.2 × 10 10 to 9.7 × 10 12 molecules cm −3 s −1 , respectively. Like OH, Cl facilitated multistep SOA oxidative aging over the range of OFR conditions that weremore »studied. In contrast, the extent of Br-initiated SOA oxidative aging was limited. SOA elemental ratios and mass yields obtained in the OFR studies were comparable to those obtained from OH and Cl oxidation of the same precursors in environmental chamber studies. Overall, our results suggest that alkane, aromatic, and terpenoid SOA precursors are characterized by distinct OH- and halogen-initiated SOA yields, and that while Cl may enhance the SOA formation potential in regions influenced by biogenic and anthropogenic emissions, Br may have the opposite effect.« less
5. Inequality in air pollution mortality from power generation in India

   https://doi.org/10.1088/1748-9326/aca8bb  

   Sengupta, Shayak ; Thakrar, Sumil K. ; Singh, Kirat ; Tongia, Rahul ; Hill, Jason D. ; Azevedo, Ines M. L. ; Adams, Peter J. ( December 2022 , Environmental Research Letters)

   India’s coal-heavy electricity system is the world’s third largest and a major emitter of air pollution and greenhouse gas emissions. Consequently, it remains a focus of decarbonization and air pollution control policy. Considerable heterogeneity exists between states in India in terms of electricity demand, generation fuel mix, and emissions. However, no analysis has disentangled the expected, state-level spatial differences and interactions in air pollution mortality under current and future power sector policies in India. We use a reduced-complexity air quality model to evaluate annual PM_2.5mortalities associated with electricity production and consumption in each state in India. Furthermore, we test emissions control, carbon tax, and market integration policies to understand how changes in power sector operations affect ambient PM_2.5concentrations and associated mortality. We find poorer, coal-dependent states in eastern India disproportionately face the burden of PM_2.5mortality from electricity in India by importing deaths. Wealthier, high renewable energy states in western and southern India meanwhile face a lower burden by exporting deaths. This suggests that as these states have adopted more renewable generation, they have shifted their coal generation and associated PM_2.5mortality to eastern areas. We also find widespread sulfur emissions control decreases mortality by about 50%. Likewise, increasing carbon taxesmore »in the short term reduces annual mortality by up to 9%. Market reform where generators between states pool to meet demand reduces annual mortality by up to 8%. As India looks to increase renewable energy, implement emissions control regulations, establish a carbon trading market, and move towards further power market integration, our results provide greater spatial detail for a federally structured Indian electricity system.

   « less