The Kathmandu Valley in Nepal suffers from unhealthy air quality, with mean pre-monsoon submicron particulate matter concentration (PM1) of 40 µg m-3 and daily peaks over 75 µg m-3. A...

Randomization of hospitalized patients admitted for chest pain work-up to either CCTA or to stress testing resulted in similar discharge times, change in medical therapies at discharge, frequency of downstream noninvasive testing, and repeat hospitalizations. However, a higher frequency of invasive coronary angiography and revascularization procedures were performed in the CCTA arm. (ClinicalTrials.gov number, NCT01604655.).

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The Kathmandu valley experiences an average wintertime PM1 concentration of ∼100 μg m–3 and daily peaks over 200 μg m–3. We present ambient nonrefractory PM1 chemical composition, and concentration measured by a mini aerosol mass spectrometer (mAMS) sequentially at Dhulikhel (on the valley exterior), then urban Ratnapark, and finally suburban Lalitpur in winter 2018. At all sites, organic aerosol (OA) was the largest contributor to combined PM1 (C-PM1) (49%) and black carbon (BC) was the second largest contributor (21%). The average background C-PM1 at Dhulikhel was 48 μg m–3; the urban enhancement was 120% (58 μg m–3). BC had an average of 6.1 μg m–3 at Dhulikhel, an urban enhancement of 17.4 μg m–3. Sulfate (SO4) was 3.6 μg m–3 at Dhulikhel, then 7.5 μg m–3 at Ratnapark, and 12.0 μg m–3 at Lalitpur in the brick kiln region. Chloride (Chl) increased by 330 and 250% from Dhulikhel to Ratnapark and Lalitpur on average. Positive matrix factorization (PMF) identified seven OA sources, four primary OA sources, hydrocarbon-like (HOA), biomass burning (BBOA), trash burning (TBOA), a sulfate-containing local OA source (sLOA), and three secondary oxygenated organic aerosols (OOA). OOA was the largest fraction of OA, over 50% outside the valley and 36% within. HOA (traffic) was the most prominent primary source, contributing 21% of all OA and 44% of BC. Brick kilns were the second largest contributor to C-PM1, 12% of OA, 33% of BC, and a primary emitter of aerosol sulfate. These results, though successive, indicate the importance of multisite measurements to understand ambient particulate matter concentration heterogeneity across urban regions.

<p><strong>Abstract.</strong> Semi continuous PM<sub>2.5</sub> and BC concentrations, and 24-hour integrated PM<sub>2.5</sub> filter samples were collected near roadways in the Kathmandu Valley, Nepal. Instruments were carried by a group of volunteer traffic police officers in the vicinity of six major roadway intersections in the Kathmandu Valley across two sampling periods in 2014. Daily PM<sub>2.5</sub> filter samples were analyzed for water soluble inorganic ions, elemental carbon (EC) and organic carbon (OC), and 24 elements. Mean PM<sub>2.5</sub> and BC concentrations were 124.76 μg m<sup>−3</sup> and 16.74 μgC m<sup>−3</sup> during the drier spring sampling period, and 45.92 μg m<sup>−3</sup> and 13.46 μgC m<sup>−3</sup> during monsoonal sampling. Despite the lower monsoonal PM<sub>2.5</sub> concentrations, BC and several elements were not significantly lower during the monsoon, which indicates an important contribution of vehicle-related emissions throughout both seasons in this region. During the monsoon, there was an enhanced contribution of chemical species (elements and water soluble inorganic ions) except secondary inorganic ions, and BC to PM<sub>2.5</sub> (crustal elements: 19 %; heavy metals: 5 %; BC: 39 %) compared to those in spring (crustal elements: 9 %; heavy metals: 1 %; BC: 18 %). Silica, calcium, aluminum, and iron were the most abundant elements during both spring and the monsoon, with the total concentrations of 12.13 and 8.85 μg m<sup>−3</sup>, respectively. PM<sub>2.5</sub> and BC showed less spatial variation compared to that for individual chemical species.</p>