NOx instrument intercomparison for laboratory biomass burning source studies and urban ambient measurements in Albuquerque, New Mexico.

Understanding nitrogen oxides (NOx = NO + NO2) measurement techniques is important as air-quality standards become more stringent, important sources change, and instrumentation develops. NOx observations are compared in two environments: source testing from the combustion of Southwestern biomass fuels, and urban, ambient NOx. The latter occurred in the urban core of Albuquerque, NM, at an EPA NCORE site during February-March 2017, a relatively clean photochemical environment with ozone (O3) <60 ppb for all but 6 hr. We compare two techniques used to measure NOx in biomass smoke during biomass burning source testing: light absorption at 405 nm and a traditional chemiluminescence monitor. Two additional oxides of nitrogen techniques were added in urban measurements: a cavity attenuated phase shift instrument for direct NO2, and the NOy chemiluminescence instrument (conversion of NOy to NO by molybdenum catalyst). We find agreement similar to laboratory standards for NOx, NO2, and NO comparing all four instruments (R2 > 0.97, slopes between 0.95 and 1.01, intercepts < 2 ppb for 1-hr averages) in the slowly varying ambient setting. Little evidence for significant interferences in NO2 measurements was observed in comparing techniques in late-winter urban Albuquerque. This was also confirmed by negligible NOz contributions as measured with an NOy instrument. For the rapidly varying (1-min) higher NOx concentrations in biomass smoke source testing, larger variability characterized chemiluminescence and absorption instruments. Differences between the two instruments were both positive and negative and occurred for total NOx, NO, and NO2. Nonetheless, integrating the NOx signals over an entire burn experiment and comparing 95 combustion experiments, showed little evidence for large systematic influences of possible interfering species biasing the methods. For concentrations of <2 ppm, a comparison of burn integrated NOx, NO2, and NO yielded slopes of 0.94 to 0.96, R2 of 0.83 to 0.93, and intercepts of 8 to 25 ppb. We attribute the latter, at least in part, to significant noise particularly at low NOx concentrations, resulting from short averaging times during highly dynamic lab burns. Discrepancies between instruments as indicated by the intercepts urge caution with oxides of nitrogen measurements at concentrations <50 ppb for rapidly changing conditions. Implications: Multiple NOx measurement methods were employed to measure NOx concentrations at an EPA NCORE site in Albuquerque, NM, and in smoke produced by the combustion of Southwestern biomass fuels. Agreement shown during intercomparison of these NOx techniques indicated little evidence of significant interfering species biasing the methods in these two environments. Instrument agreement is important to understand for accurately characterizing ambient NOx conditions in a range of environments.

Is NSQIP Pediatric review representative of total institutional experience for children undergoing appendectomy?

BACKGROUND/PURPOSE: NSQIP Pediatric (NSQIP-P) is a robust quality improvement effort. A limitation of the NSQIP process lies in capturing a small proportion of the total case volume. This study examines whether appendectomies captured by NSQIP-P are concordant with all appendectomies, the most commonly captured procedure in 2011. METHODS: We compared case mix and 30-day outcomes between children undergoing an appendectomy who were included in NSQIP (n=80) and children not captured by NSQIP (n=276) during 2011 at a tertiary referral children's hospital. A single surgical case reviewer reviewed all cases using NSQIP-P methodology. RESULTS: NSQIP-P captured 80 of a total of 356 appendectomies (22%). The case mix was similar between NSQIP and non-NSQIP groups (e.g., 31% of each group had complicated appendicitis). Outcomes were also similar; post-operative occurrences, readmissions and return to the operation room occurred at rates of 7.5% vs. 7.6%, 5% vs. 4.7%, and 3.8% vs. 4.3% respectively. CONCLUSION: Although NSQIP-P captured a minority of the total patient population that had an appendectomy, the case mix and outcomes were similar. Our results offer reassurance that NSQIP-P data are representative of the larger population for this procedure. Whether this concordance exists for procedures less commonly performed is unknown and a focus of ongoing work.