Measurement of NO_<i>x</i> Fluxes from a Tall Tower in Central London, UK and Comparison with Emissions Inventories

Direct measurements of NO_<i>x</i> concentration and flux were made from a tall tower in central London, UK as part of the Clean Air for London (ClearfLo) project. Fast time resolution (10 Hz) NO and NO₂ concentrations were measured and combined with fast vertical wind measurements to provide top-down flux estimates using the eddy covariance technique. Measured NO_<i>x</i> fluxes were usually positive and ranged from close to zero at night to 2000–8000 ng m^–2 s^–1 during the day. Peak fluxes were usually observed in the morning, coincident with the maximum traffic flow. Measurements of the NO_<i>x</i> flux have been scaled and compared to the UK National Atmospheric Emissions Inventory (NAEI) estimate of NO_<i>x</i> emission for the measurement footprint. The measurements are on average 80% higher than the NAEI emission inventory for all of London. Observations made in westerly airflow (from parts of London where traffic is a smaller fraction of the NO_<i>x</i> source) showed a better agreement on average with the inventory. The observations suggest that the emissions inventory is poorest at estimating NO_<i>x</i> when traffic is the dominant source, in this case from an easterly direction from the BT Tower. Agreement between the measurements and the London Atmospheric Emissions Inventory (LAEI) are better, due to the more explicit treatment of traffic flow by this more detailed inventory. The flux observations support previous tailpipe observations of higher NO_<i>x</i> emitted from the London vehicle diesel fleet than is represented in the NAEI or predicted for several EURO emission control technologies. Higher-than-anticipated vehicle NO_<i>x</i> is likely responsible for the significant discrepancies that exist in London between observed NO_<i>x</i> and long-term NO_<i>x</i> projections

Demographic and behavioral characteristics of 803 black and white non-Hispanic MSM at enrollment in the <i>InvolveMENt</i> study.

<p>** Options for other non-injection drugs included: Crystal meth, crack, cocaine, downers, painkillers, hallucinogens, ecstasy, special K, GHB.</p

Enrollment scheme and results for recruitment of a black/white HIV/STI incidence cohort, Atlanta, 2010–2012.

<p>Men recruited through Facebook were screened for eligibility criteria online; men who met eligibility criteria in their online screening were invited to attend an in-person baseline (enrollment) visit. *Participant may have more than once reason for ineligibility. **The race of 3 participants was adjusted once they attended their baseline visit due to incorrect screening races being recorded.</p

Biomedical measures on 803 black and white non-Hispanic MSM at enrollment in the <i>InvolveMENt</i> study.

<p>Biomedical measures on 803 black and white non-Hispanic MSM at enrollment in the <i>InvolveMENt</i> study.</p

Distribution of residence of MSM enrolled in a cohort study of men who have sex with men in Atlanta, June 2010-December 2012.

<p>Distribution of residence of MSM enrolled in a cohort study of men who have sex with men in Atlanta, June 2010-December 2012.</p

Census tract characteristics of census tracts in which 797 black and white non-Hispanic MSM resided at enrollment in the <i>InvolveMENt</i> study.

<p>A total of 350 unique census tracts were included in the analysis; there are 946 census tracts in the Atlanta MSA, which was the catchment area for the study. Because we calculated the mean of census tracts where the participants lived, the number of items of census tract data included in the average was equal to the number of participants for all calculations except for HIV diagnosis rate. Diagnosis rates are missing for 49 individuals who lived in census tracts not included in the data released from the state and for 40 individuals who lived in census tracts for which the numerator (number of persons living with an HIV infection diagnosis) was less than 5 and/or the denominator (number of people in the census tract in that population group) was <500.</p

Characteristics of 2,913 partnerships reported by 803 black and white non-Hispanic MSM at enrollment in the <i>InvolveMENt</i> study.

<p>Characteristics of 2,913 partnerships reported by 803 black and white non-Hispanic MSM at enrollment in the <i>InvolveMENt</i> study.</p