Abstract. In order to determine the wavelength dependence of fine (<1 micron) atmospheric aerosol absorption in the Mexico City area, the absorptionÅngstrom exponents (AAEs) were calculated from hourly averages of aerosol absorption measured at seven wavelengths (370, 450, 520, 590, 660, 880, and 950 nm) The AAE values determined in the afternoon were consistently higher than the corresponding morning values, suggesting the photochemical aging of the aerosols leading to the formation of more highly UV absorbing organic aerosol species in the afternoon.The AAE values were compared to stable and radiocarbon isotopic measurements of the 12-h aerosol samples to determine the sources of the aerosol carbon. The fraction of modern carbon (fM) in the aerosol samples, as determined from 14 C analysis, showed that an average of 70% of the carbonaceous aerosols in Mexico City were from modern biomass sources during both field campaigns. The 13 C/ 12 C ratios of

Background/Aims: To compare the gestational weight gain and adverse perinatal outcomes in urban Mexican women with prepregnancy overweight or obesity, under an early intensive obstetric and nutrition program versus women with prepregnancy normal weight. Methods: A cohort of 546 pregnant women with prepregnancy normal weight (n = 201, NW), overweight (n = 171, OW) or obesity (n = 174, OB), ≤13 weeks of gestation and a singleton pregnancy. OW and OB groups were under early intensive obstetric and nutritional care and NW group was under routine prenatal care. Miscarriage, hypertensive disorders, premature rupture of membranes, preterm birth, stillbirth, gestational diabetes mellitus (GDM) and large- or small-for-gestational-age newborns, were compared between groups. Results: Weight gain was smaller in OB than in OW or NW (mean ± SD): 6.1 ± 4.4, 9.5 ± 5.1, 10.3 ± 5.4 kg, respectively (p < 0.001). OB women had the highest frequency of GDM (p < 0.001), lack of spontaneous labor (p < 0.001) and preeclampsia (p < 0.001), but no other between-group differences existed. Conclusion: Early intensive medical-nutrition prenatal care and adequate gestational weight gain may contribute to decreasing most maternal and newborn adverse outcomes associated with prepregnancy overweight or obesity.

Abstract. In order to determine the wavelength dependence of atmospheric aerosol absorption in the Mexico City area, the absorption Ångstrom exponents (AAEs) were calculated from aerosol absorption measurements at seven wavelengths obtained with a seven-channel aethalometer during two field campaigns, the Mexico City Metropolitan Area study in April 2003 (MCMA 2003) and the Megacity Initiative: Local and Global Research Observations in March 2006 (MILAGRO). The AAEs varied from 0.76 to 1.56 in 2003 and from 0.54 to 1.52 in 2006. The AAE values determined in the afternoon were consistently higher than the corresponding morning values, suggesting the photochemical formation of absorbing secondary organic aerosols (SOA) in the afternoon. The AAE values were compared to stable and radiocarbon isotopic measurements of aerosol samples collected at the same time to determine the sources of the aerosol carbon. The fraction of modern carbon (fM) in the aerosol samples, as determined from 14C analysis, showed that 70% of the carbonaceous aerosols in Mexico City were from modern sources, indicating a significant impact from biomass burning during both field campaigns. The 13C/12C ratios of the aerosol samples illustrate the significant impact of Yucatan forest fires (C-3 plants) in 2003 and local grass fires (C-4 plants) at site T1 in 2006. A direct comparison of the fM values, stable carbon isotope ratios, and calculated aerosol AAEs suggested that the wavelength dependence of the aerosol absorption was controlled by the biogenically derived aerosol components.

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