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We describe the characterization and field deployment of chemical ionization mass spectrometry (CIMS) using a recently developed focusing ion-molecule reactor (FIMR) and ammonium–water cluster (NH4+⋅H2O) as the reagent ion (denoted as NH4+ CIMS). We show that NH4+⋅H2O is a highly versatile reagent ion for measurements of a wide range of oxygenated organic compounds. The major product ion is the cluster with NH4+ produced via ligand-switching reactions. Other product ions (e.g., protonated ion, cluster ion with NH4+⋅H2O , with H3O+ , and with H3O+⋅H2O) are also produced, but with minor fractions for most of the oxygenated compounds studied here. The instrument sensitivities (ion counts per second per part per billion by volume, cps ppbv -1) and product distributions are strongly dependent on the instrument operating conditions, including the ratio of ammonia (NH3) and H2O flows and the drift voltages, which should be carefully selected to ensure NH4+⋅H2O as the predominant reagent ion and to optimize sensitivities. For monofunctional analytes, the NH4+⋅H2O chemistry exhibits high sensitivity (i.e., >1000 cps ppbv -1) to ketones, moderate sensitivity (i.e., between 100 and 1000 cps ppbv -1) to aldehydes, alcohols, organic acids, and monoterpenes, low sensitivity (i.e., between 10 and 100 cps ppbv -1) to isoprene and C1 and C2 organics, and negligible sensitivity (i.e., <10 cps ppbv -1) to reduced aromatics. The instrumental sensitivities of analytes depend on the binding energy of the analyte– NH4+ cluster, which can be estimated using voltage scanning. This offers the possibility to constrain the sensitivity of analytes for which no calibration standards exist. This instrument was deployed in the RECAP campaign (Re-Evaluating the Chemistry of Air Pollutants in California) in Pasadena, California, during summer 2021. Measurement comparisons against co-located mass spectrometers show that the NH4+ CIMS is capable of detecting compounds from a wide range of chemical classes. The NH4+ CIMS is valuable for quantification of oxygenated volatile organic compounds (VOCs) and is complementary to existing chemical ionization schemes. [ABSTRACT FROM AUTHOR]

• We surveyed California members of KnowledgePanel®, a probability-based panel. • We estimated ordered and generalized structural equation models. • We analyzed the association between environmental justice and grocery shopping. • Higher levels of environmental injustice are associated with less in-store shopping. • There is no association between environmental justice, e-grocery, & click-and-pick. To understand how COVID-19 changed grocery shopping and explore implications for transportation and environmental justice, we surveyed in May 2021 California members of KnowledgePanel®, the largest and oldest U.S. probability-based panel. We asked how frequently Californians grocery shopped before and during the pandemic, and how they may grocery shop afterward in-store, online with home delivery ("e-grocery"), or online with store/curbside pick-up ("click-and-pick"). We found that most Californians continued to grocery shop in-person during the pandemic, although less frequently than before. Many relied more on e-grocery (+8.9 %) and click-and-pick (+13.3 %), although older generations remained attached to in-store shopping. African American households grocery shopped in-store less than Whites pre-pandemic; post-pandemic, they may compensate with more e-grocery and click-and-pick. While higher levels of environmental injustice (based on CalEnviroScreen) were associated with less in-store shopping, we found no association with e-grocery or click-and-pick. Our results have implications for travel, food logistics, and parking management. [ABSTRACT FROM AUTHOR]