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External cycling regenerating nitrogen oxides (NOx ≡ NO + NO2) from their oxidative reservoir, NOz, is proposed to reshape the temporal-spatial distribution of NOx and consequently hydroxyl radical (OH), the most important oxidant in the atmosphere. Here we verify the in situ external cycling of NOx in various environments with nitrous acid (HONO) as an intermediate based on synthesized field evidence collected onboard aircraft platform at daytime. External cycling helps to reconcile stubborn underestimation on observed ratios of HONO/NO2 and NO2/NOz by current chemical model schemes and rationalize atypical diurnal concentration profiles of HONO and NO2 lacking noontime valleys specially observed in low-NOx atmospheres. Perturbation on the budget of HONO and NOx by external cycling is also found to increase as NOx concentration decreases. Consequently, model underestimation of OH observations by up to 41% in low NOx atmospheres is attributed to the omission of external cycling in models.

This study investigated the prevalence of increasingly popular animal-assisted stress relief programs at higher education institutions across the United States. Although research on animal-assisted programs is increasing, there is still a lack of information documenting implementation of these programs. Therefore, the purpose of this study was to explore the prevalence, structure, and policies around animal-assisted programs. Data from 68 schools across the U.S. revealed that animal visitation at higher education institutions is popular, and some schools have instituted formalized programs. However, there is an overall lack of knowledge regarding standards and requirements that would increase the safety and effectiveness of these programs.

External cycling regenerating nitrogen oxides (NOx ≡ NO + NO2) from their oxidative reservoir, NOz, is proposed to reshape the temporal–spatial distribution of NOx and consequently hydroxyl radical (OH), the most important oxidant in the atmosphere. Here we verify the in situ external cycling of NOx in various environments with nitrous acid (HONO) as an intermediate based on synthesized field evidence collected onboard aircraft platform at daytime. External cycling helps to reconcile stubborn underestimation on observed ratios of HONO/NO2 and NO2/NOz by current chemical model schemes and rationalize atypical diurnal concentration profiles of HONO and NO2 lacking noontime valleys specially observed in low-NOx atmospheres. Perturbation on the budget of HONO and NOx by external cycling is also found to increase as NOx concentration decreases. Consequently, model underestimation of OH observations by up to 41% in low NOx atmospheres is attributed to the omission of external cycling in models.External cycling regenerates nitrogen oxides from the NOx oxidative reservoir, NOz. Aircraft observations reveal NOx external cycling compensates for NOx aging, sustaining NOx distribution and production of OH radicals far from NOx emission sources [ABSTRACT FROM AUTHOR]

Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere (1). Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides (1). However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed (2,3). A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies (2-4), but the mechanisms responsible for this process remain uncertain (5-9). Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism (10,11) suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale., Nitrogen oxides ([NO.sub.x] =N O and N[O.sub.2]) are essential in the formation of secondary aerosol and atmospheric oxidants, such as ozone ([O.sub.3]) and hydroxyl radicals (OH) (1). Nitric acid (HN[O.sub.3]) [...]

Detection of in-flight icing hazard is a priority of the aviation safety community. The "Radar Icing Algorithm" (RadIA) has been developed to indicate the presence, phase, and relative size of supercooled drops. This paper provides an evaluation of RadIA via comparison to in situ microphysical measurements collected with a research aircraft during the 2017 "Seeded and Natural Orographic Wintertime clouds: the Idaho Experiment" (SNOWIE) field campaign. RadIA uses level-2 dual-polarization radar moments from operational National Weather Service WSR-88D and a numerical weather prediction model temperature profile as inputs. Moment membership functions are defined based on the results of previous studies, and fuzzy logic is used to combine the output of these functions to create a 0 to 1 interest for detecting small-drop, large-drop, and mixed-phase icing. Data from the two-dimensional stereo (2D-S) particle probe on board the University of Wyoming King Air aircraft were categorized as either liquid or solid phase water with a shape classification algorithm and binned by size. RadIA interest values from 17 cases were matched to statistical measures of the solid/liquid particle size distributions (such as maximum particle diameter) and values of LWC from research aircraft flights. Receiver operating characteristic area under the curve (AUC) values for RadIA algorithms were 0.75 for large-drop, 0.73 for small-drop, and 0.83 for mixed-phase cases. RadIA is proven to be a valuable new capability for detecting the presence of in-flight icing hazards from ground-based precipitation radar. [ABSTRACT FROM AUTHOR]

Here we report the measurement results of nitrous acid (HONO) and a suite of relevant parameters on the NCAR C-130 research aircraft in the Southeast U.S. during NOMADSS 2013 summer field study. Daytime HONO concentrations ranged from low parts per trillion by volume (pptv) in the free troposphere (FT) to mostly within 5–15 pptv in the background terrestrial air masses, and to up to 40 pptv in the industrial and urban plumes in the planetary boundary layer (PBL). There was no discernable vertical HONO distribution trend in the PBL above the lowest flight altitude of 300 m, indicating that the ground surface HONO source was not a significant contributor to the HONO budget in the measurement altitude between 300 m and 4.7 km. While there was a strong correlation between the concentrations of HONO and oxides of nitrogen (NOx = NO + NO2) (R2 = 0.52), the sum of all known NOx-related HONO formation mechanisms was found to account for less 20 % of the daytime HONO source in the background terrestrial air masses, due to the low level of NOx and surface area density of aerosol particles. Photolysis of particulate nitrate (pNO3) appeared to be the major daytime HONO source in the background terrestrial air masses, based on the measured pNO3 concentration and the median value of 2.0 × 10−4 s−1 for pNO3 photolysis rate constant determined in the laboratory using ambient aerosol samples collected during the field study. Within the power plant and industrial plumes encountered, daytime HONO was predominantly produced by secondary formation processes involving both NOx and pNO3 as precursors. While HONO was not a significant OH precursor compared to O3 under low NOx conditions in the air column, it was an important intermediate product of a photochemical renoxification process recycling nitric acid and nitrate back to NOx. Finally, the HONO / NOx ratio stayed relatively constant for several hours after sunset in the nocturnal residual layer, suggesting no significant night-time volume HONO source existed in the nocturnal residual layer and the nocturnal FT under background conditions. [ABSTRACT FROM AUTHOR]

Halogens in the troposphere are increasingly recognized as playing an important role for atmospheric chemistry, and possibly climate. Bromine and iodine react catalytically to destroy ozone (O3), oxidize mercury, and modify oxidative capacity that is relevant for the life-time of greenhouse gases. Most of the tropospheric O3 and methane (CH4) loss occurs at tropical latitudes. Here we report simultaneous measurements of vertical profiles of bromine oxide (BrO) and iodine oxide (IO) in the tropical and subtropical free troposphere (10°N to 40°S), and show that these halogens are responsible for 34% of the column-integrated loss of tropospheric O3. The observed BrO concentrations increase strongly with altitude (~3.4 pptv at 13.5 km), and are 2-4 times higher than predicted in the tropical free troposphere. BrO resembles model predictions more closely in stratospheric air. The largest model low bias is observed in the lower tropical transition layer (TTL) over the tropical eastern Pacific Ocean, and may reflect a missing inorganic bromine source supplying an additional 2.5-6.4 pptv total inorganic bromine (Bry), or model overestimated Bry wet scavenging. Our results highlight the importance of heterogeneous chemistry on ice clouds, and imply an additional Bry source from the debromination of sea salt residue in the lower TTL. The observed levels of bromine oxidize mercury up to 3.5 times faster than models predict, possibly increasing mercury deposition to the ocean. The halogen-catalyzed loss of tropospheric O3 needs to be considered when estimating past and future ozone radiative effects. [ABSTRACT FROM AUTHOR]