Author Correction: Global and regional trends of atmospheric sulfur.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Global and regional trends of atmospheric sulfur.

The profound changes in global SO2 emissions over the last decades have affected atmospheric composition on a regional and global scale with large impact on air quality, atmospheric deposition and the radiative forcing of sulfate aerosols. Reproduction of historical atmospheric pollution levels based on global aerosol models and emission changes is crucial to prove that such models are able to predict future scenarios. Here, we analyze consistency of trends in observations of sulfur components in air and precipitation from major regional networks and estimates from six different global aerosol models from 1990 until 2015. There are large interregional differences in the sulfur trends consistently captured by the models and observations, especially for North America and Europe. Europe had the largest reductions in sulfur emissions in the first part of the period while the highest reduction came later in North America and East Asia. The uncertainties in both the emissions and the representativity of the observations are larger in Asia. However, emissions from East Asia clearly increased from 2000 to 2005 followed by a decrease, while in India a steady increase over the whole period has been observed and modelled. The agreement between a bottom-up approach, which uses emissions and process-based chemical transport models, with independent observations gives an improved confidence in the understanding of the atmospheric sulfur budget.

Predicting the risk of soybean rust in Minnesota based on an integrated atmospheric model.

To minimize crop loss by assisting in timely disease management and reducing fungicide use, an integrated atmospheric model was developed and tested for predicting the risk of occurrence of soybean rust in Minnesota. The model includes a long-range atmospheric spore transport and deposition module coupled to a leaf wetness module. The latter is required for spore germination and infection. Predictions are made on a daily basis for up to 7 days in advance using forecast data from the United States National Weather Service. Complementing the transport and leaf wetness modules, bulk (wet plus dry) atmospheric deposition samples from Minnesota were examined for soybean rust spores using a specific DNA test and sequence analysis. Overall, the risk prediction worked satisfactorily within the bounds of the uncertainty associated with the use of modeled 7-day weather forecasts, with more than 65% agreement between the model forecast and the DNA test results. The daily predictions are available as an advisory to the user community through the University of Minnesota Extension. However, users must take the actual decision to implement the disease management strategy.

Uncertainties in the current knowledge of some atmospheric trace gases associated with U.S. agriculture: a review.

Approximately 80 different crop species are grown in the United States in widely differing geographic areas, climatic and edaphic conditions, and management practices. Although the majority of cultivated acreage in the United States is planted with only about 10 primary crops, uncertainties associated with trace gas emissions arise from: (1) limited data availability, (2) inaccurate estimates because of large temporal and spatial variability in trace gas composition and magnitude of trace gas emissions from agricultural activities, (3) differing characteristics of pollutant emissions from highly dispersed animal feed-lots, and (4) limited understanding of the emissions of semi-volatile organic compounds (SVOCs) associated with agriculture. Although emission issues are of concern, so also is atmospheric deposition to cropping systems, including wet and dry nitrogen, minerals, and organic compounds. These can have feedback effects on trace gas emissions. Overall, the many gaps in our understanding of these aspects of agricultural systems deserve serious attention.

Introduction of Asian Soybean Rust Urediniospores into the Midwestern United States-A Case Study.

In 2005, weekly rain samples collected at 124 National Atmospheric Deposition Program/National Trends Network (NADP/NTN) sites in the eastern and central United States were screened for Asian soybean rust (ASR; Phakopsora pachyrhizi) urediniospores. Application of a quantitative polymerase chain reaction method detected P. pachyrhizi DNA in the filter residue of rain samples collected during the week of 19 to 26 July 2005 in Minnesota, Missouri, and South Dakota. To determine the geographic origin of ASR urediniospores in those weekly composite samples, back air trajectories of the lifted condensation and mixed boundary layers were calculated for each rain event within the week, by sampling site. The calculations, based on the hybrid single-particle lagrangian integrated trajectory model, pointed to source areas in eastern and southern Texas. In a separate case, DNA of P. pachyrhizi was detected in a 28 June to 5 July 2005 rain sample from an eastern Texas site. Back trajectories pointed to southern Texas and the Yucatan Peninsula in Mexico as potential source areas of ASR urediniospores. Vertical motions of those back trajectories indicated a ventilation of the boundary layer in the upwind areas, suggesting the possible injection of urediniospores into the free troposphere where they can be transported for long distances before wet deposition.

Spatial and temporal trends of precipitation chemistry in the United States, 1985-2002.

A Seasonal Kendall Trend (SKT) test was applied to precipitation-weighted concentration data from 164 National Atmospheric Deposition Program National Trends Network (NADP/NTN) sites operational from 1985 to 2002. Analyses were performed on concentrations of ammonium, sulfate, nitrate, dissolved inorganic nitrogen (DIN, sum of nitrogen from nitrate and ammonium), and earth crustal cations (ECC, sum of calcium, magnesium, and potassium). Over the 18-year period, statistically significant (p< or =0.10) increases in ammonium concentrations occurred at 93 sites (58%), while just three sites had statistically significant ammonium decreases. Central and northern Midwestern states had the largest ammonium increases. The generally higher ammonium concentrations were accompanied by significant sulfate decreases (139 sites, 85%), and only one significant increase which occurred in Texas. In the west central United States there were significant nitrate increases (45 sites, 27%), while in the northeastern United States there were significant decreases (25 sites, 15%). Significant DIN decreases were observed in the northeastern United States (11 sites, 7%); elsewhere there were significant increases at 75 sites (46%). ECC decreased significantly at 65 sites (40%), predominantly in the central and southern United States, and increased at 11 sites (7%). The concentrations of sulfate, nitrate, and ammonium in precipitation have changed markedly over the time period studied. Such trends indicate changes in the mix of gases and particles scavenged by precipitation, possibly reflecting changes in emissions, atmospheric chemical transformations, and weather patterns.