RESUMO
In Latin America, atmospheric deposition is a major vector of nitrogen (N) input to urban systems. Yet, measurements of N deposition are sparse, precluding analysis of spatial patterns, temporal trends, and ecosystem impacts. Chemical transport models can be used to fill these gaps in the absence of dense measurements. Here, we evaluate the performance of a global 3-D chemical transport model in simulating spatial and interannual variation in wet inorganic N (NH4-N + NO3-N) deposition across urban areas in Latin America. Monthly wet and dry inorganic N deposition to Latin America were simulated for the period 2006-2010 using the GEOS-Chem Chemical Transport Model. Published estimates of observed wet or bulk inorganic N deposition measured between 2006-2010 were compiled for 16 urban areas and then compared with model output from GEOS-Chem. Observed mean annual inorganic N deposition to the urban study sites ranged from 5.7-14.2 kg ha-1 yr-1, with NH4-N comprising 48-90% of the total. Results show that simulated N deposition was highly correlated with observed N deposition across sites (R2 = 0.83, NMB = -50%). However, GEOS-Chem generally underestimated N deposition to urban areas in Latin America compared to observations. Underestimation due to bulk sampler dry deposition artifacts was considered and improved bias without improving correlation. In contrast to spatial variation, the model did not capture year-to-year variation well. Discrepancies between modeled and observed values exist, in part, because of uncertainties in Latin American N emissions inventories. Our findings indicate that even at coarse spatial resolution, GEOS-Chem can be used to simulate N deposition to urban Latin America, improving understanding of regional deposition patterns and potential ecological effects.
RESUMO
STUDY OBJECTIVE: To assess the efficacy of single-dose sodium zirconium cyclosilicate (SZC) compared to the FDA approved three times daily (TID) dosing and to single-dose sodium polystyrene sulfonate (SPS) for the management of asymptomatic hyperkalemia in hospitalized patients. DESIGN: Single-center retrospective chart review. SETTING: University of Florida Health Jacksonville, a 695-bed academic medical center in Jacksonville, FL, between June 15, 2018 and August 15, 2021. PATIENTS: Three hundred fifty-one adult patients who were admitted to any hospital unit in the specified timeframe and received one of three interventions for asymptomatic hyperkalemia (serum potassium ≥4.7 mmol/L) were included in this study. INTERVENTION: The interventions compared were single-dose SZC 10 g, SZC 10 g × 3 doses (30 g total) within 24 h, or SPS 15-30 g once. MEASUREMENTS AND MAIN RESULTS: The primary outcome was the proportion of patients achieving normokalemia (K+ 3.3-4.6 mmol/L) within 12-30 h of the first study dose. Secondary outcomes included average change in potassium within 12-30 h and 3-54 h from the first dose. The primary outcome was met in 68 patients (58.1%) in the SZC 10 g group, 51 (43.6%) in the SZC 10 g × 3 doses group, and 81 (69.2%) in the SPS 15-30 g group (p < 0.01). The average reduction in potassium in 12-30 h was 0.70 mmol/L, 0.78 mmol/L, and 0.99 mmol/L in the SZC 10 g, SZC 10 g × 3 doses, and SPS 15-30 g groups, respectively (p < 0.01). CONCLUSIONS: SZC 10 g once resulted in more patients achieving normokalemia compared to SZC 10 g × 3 doses but less than SPS (p < 0.01). Single-dose SZC may be a reasonable option to manage asymptomatic hyperkalemia in the hospital setting, but achieving normokalemia with one dose may be less likely in patients with higher baseline potassium concentrations and impaired renal function.