Implications of Organic Mass to Carbon Ratios Increasing Over Time in the Rural United States

The thermal evolution procedure used by most monitoring programs in the United States to determine carbonaceous aerosol concentrations is referred to as the thermal‐optical reflectance method, where an aerosol sample that has been collected on a quartz filter is heated and evolved carbon is characterized as either organic (OC) or light absorbing carbon (LAC). Evolved carbon assigned to OC is multiplied by a factor, Roc, to achieve an estimate of organic mass. Over the last 10–15 years, Roc, estimated through multiple linear regression analysis of data collected in the Interagency Monitoring of Protected Visual Environments (IMPROVE) program, has increased at about a rate of about 0.02 per year, reaching values above 2.0 in many regions of the United States. Analysis of evolved carbon concentration temporal trends suggests that thermal‐optical reflectance analysis, on the average, inaccurately bifurcates particulate carbon into the OC and LAC fractions with some LAC being inadvertently and wrongly assigned to the OC fraction. It is shown that misapportioned LAC assigned to OC is decreasing faster than true OC, resulting in a compensating increase in the Roc assigned to reported OC over time. A first‐order model is proposed to correct for the misapportioned carbon

Implications of Organic Mass to Carbon Ratios Increasing Over Time in the Rural United States

The thermal evolution procedure used by most monitoring programs in the United States to determine carbonaceous aerosol concentrations is referred to as the thermal‐optical reflectance method, where an aerosol sample that has been collected on a quartz filter is heated and evolved carbon is characterized as either organic (OC) or light absorbing carbon (LAC). Evolved carbon assigned to OC is multiplied by a factor, Roc, to achieve an estimate of organic mass. Over the last 10–15 years, Roc, estimated through multiple linear regression analysis of data collected in the Interagency Monitoring of Protected Visual Environments (IMPROVE) program, has increased at about a rate of about 0.02 per year, reaching values above 2.0 in many regions of the United States. Analysis of evolved carbon concentration temporal trends suggests that thermal‐optical reflectance analysis, on the average, inaccurately bifurcates particulate carbon into the OC and LAC fractions with some LAC being inadvertently and wrongly assigned to the OC fraction. It is shown that misapportioned LAC assigned to OC is decreasing faster than true OC, resulting in a compensating increase in the Roc assigned to reported OC over time. A first‐order model is proposed to correct for the misapportioned carbon

Dichlorodiphenyltrichloroethane in soil, river sediment, and fish in the Amazon in Brazil

Dichlorodiphenyltrichloroethane (DDT), its main metabolites, and other organochlorines were analyzed in soils (n=6), fluvial sediments (n=14), and fish (n=10) that were collected in several areas of the Amazon region in Brazil. The samples were analyzed by capillary column gas chromatography coupled to electron capture detection. DDT residues were present in most of the collected sediments in concentrations of approximately 10 to 100 Šg/kg (ppb, dry weight). Some urban top soils were found to have more than 1 mg/kg (ppm). In fish, as much as 0.5 mg/kg of total DDT (wet weight) was found in the edible parts. The presence of p,p'-DDT in most of the samples reflects the use of this insecticide against vectors of malaria between 1946 and 1993, which hasled to its ubiquitous presence in the environment of the Brazilian Amazon

Aerosol decadal trends - Part 1: In-situ optical measurements at GAW and IMPROVE stations

Currently many ground-based atmospheric stations include in-situ measurements of aerosol physical and optical properties, resulting in more than 20 long-term (>10 yr) aerosol measurement sites in the Northern Hemisphere and Antarctica. Most of these sites are located at remote locations and monitor the aerosol particle number concentration, wavelength-dependent light scattering, backscattering, and absorption coefficients. The existence of these multi-year datasets enables the analysis of long-term trends of these aerosol parameters, and of the derived light scattering A° ngstro¨m exponent and backscatter fraction. Since the aerosol variables are not normally distributed, three different methods (the seasonal Mann-Kendall test associated with the Sen’s slope, the generalized least squares fit associated with an autoregressive bootstrap algorithm for confidence intervals, and the least-mean square fit applied to logarithms of the data) were applied to detect the long-term trends and their magnitudes. To allow a comparison among measurement sites, trends on the most recent 10 and 15 yr periods were calculated. No significant trends were found for the three continental European sites. Statistically significant trends were found for the two European marine sites but the signs of the trends varied with aerosol property and location. Statistically significant decreasing trends for both scattering and absorption coefficients (mean slope of −2.0%yr−1) were found for most North American stations, although positive trends were found for a few desert and high-altitude sites. The difference in the timing of emission reduction policy for the Europe and US continents is a likely explanation for the decreasing trends in aerosol optical parameters found for most American sites compared to the lack of trends observed in Europe. No significant trends in scattering coefficient were found for the Arctic or Antarctic stations, whereas the Arctic station had a negative trend in absorption coefficient. The high altitude Pacific island station of Mauna Loa presents positive trends for both scattering and absorption coefficients

Contaminação por mercúrio em sedimento e em moluscos do Pantanal, Mato Grosso, Brasil Mercury contamination in sediment and in molluscs of Pantanal, Mato Grosso, Brazil

<abstract language="eng">The total level of mercury detected in the sediment and in the tissues of molluscs from the Bento Gomes basin, although low, have shown that the mercury used in the gold mining activities in the Poconé wetlands has contaminated those aquatic habitats in Pantanal. From 69 sediment samples analyzed, 26 % (N = 18) have shown levels ranging from 0.01 to 0.25µg.g-1 of mercury (moist weight). Mercury levels analyzed in 54 samples of mollusc tissues (Ampullaria scalaris Orbigny, 1835; A. canaliculata Lamarck, 1819 and Marisa planogyra Pilsbry, 1933) have shown that 30% (N = 16) were contaminated with levels ranging from 0.02 to 1.16µg.g-1 moist weight. This study shows that the mercury used in digs for gold mining and released into the environment has reached the habitats of Pantanal spread from the sediment into the molluscs living in the region