Contact: Mark Golden
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
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