Methods for Detecting Natural Gas Emissions (image) Stanford University Share Print E-Mail Caption Top-down methods take air samples from aircraft or tall towers to measure gas concentrations remote from sources. Bottom-up methods take measurements directly at facilities. Top-down methods provide a more complete and unbiased assessment of emissions sources, and can detect emissions over broad areas. However, they lack specificity and face difficulty in assigning emissions to particular sources. Bottom-up methods provide direct, precise measurement of gas emissions rates. However, the high cost of sampling and the need for site access permission leads to small sample sizes and possible sampling bias. Credit Stanford University School of Earth Sciences Usage Restrictions Photographs, videos and other images provided by the Precourt Institute for Energy at Stanford University are to be used - with appropriate credit - for editorial purposes only. Flopping, editing, altering or otherwise embellishing these images in any way that changes the images' editorial content is prohibited. Photographs and images provided for web use must be resized to low resolution. Permission is for one-time use only. Supplied photo/video/image file must be deleted after use. Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.