The Kathmandu Valley in Nepal suffers from severe wintertime air pollution. Volatile organic compounds (VOCs) are key constituents of air pollution, though their specific role in the valley is poorly understood due to insufficient data. During the SusKat-ABC (Sustainable Atmosphere for the Kathmandu Valley-Atmospheric Brown Clouds) field campaign conducted in Nepal in the winter of 2012-2013, a comprehensive study was carried out to characterise the chemical composition of ambient Kathmandu air, including the determination of speciated VOCs, by deploying a proton transfer reaction time-of-flight mass spectrometer (PTR-TOF-MS) -the first such deployment in South Asia. In the study, 71 ion peaks (for which measured ambient concentrations exceeded the 2σ detection limit) were detected in the PTR-TOF-MS mass scan data, highlighting the chemical complexity of ambient air in the valley. Of the 71 species, 37 were found to have campaign average concentrations greater than 200 ppt and were identified based on their spectral characteristics, ambient diel profiles and correlation with specific emission tracers as a result of the high mass resolution (m / m > 4200) and temporal resolution (1 min) of the PTR-TOF-MS. The concentration ranking in the average VOC mixing ratios dur-ing our wintertime deployment was acetaldehyde (8.8 ppb) > methanol (7.4 ppb) > acetone + propanal (4.2 ppb) > benzene (2.7 ppb) > toluene (1.5 ppb) > isoprene (1.1 ppb) > acetonitrile (1.1 ppb) > C8-aromatics (∼1 ppb) > furan (∼0.5 ppb) > C9-aromatics (0.4 ppb). Distinct diel profiles were observed for the nominal isobaric compounds isoprene (m / z = 69.070) and furan (m / z = 69.033). Comparison with wintertime measurements from several locations elsewhere in the world showed mixing ratios of acetaldehyde (∼ 9 ppb), acetonitrile (∼ 1 ppb) and isoprene (∼ 1 ppb) to be among the highest reported to date. Two "new" ambient compounds, namely formamide (m / z = 46.029) and acetamide (m / z = 60.051), which can photochemically produce isocyanic acid in the atmosphere, are reported in this study along with nitromethane (a tracer for diesel exhaust), which has only recently been detected in ambient studies. Two distinct periods were selected during the campaign for detailed analysis: the first was associated with high wintertime emissions of biogenic isoprene and the second with elevated levels of ambient acetonitrile, benzene and isocyanic acid from biomass burning activities. Emissions from biomass burning and biomass co-fired brick kilns were found to be the dominant sources for compounds such Published by Copernicus Publications on behalf of the European Geosciences Union. C. Sarkar et al.: Wintertime high acetaldehyde, isoprene and isocyanic acid in Kathmandu Valleyas propyne, propene, benzene and propanenitrile, which correlated strongly with acetonitrile (r 2 > 0.7), a chemical tracer for biomass burning. The calculated total VOC OH reactivity was dominated by acetaldehyde (24.0 %), isoprene (20.2 %) and propene (18.7 %), while oxygenated VOCs and is...

One seventh of the world's population lives in the Indo-Gangetic Plain (IGP) and the fertile region sustains agricultural food crop production for much of South Asia, yet it remains one of the most under-studied regions of the world in terms of atmospheric composition and chemistry. In particular, the emissions and chemistry of volatile organic compounds (VOCs) that form surface ozone and secondary organic aerosol through photochemical reactions involving nitrogen oxides are not well understood. In this study, ambient levels of VOCs such as methanol, acetone, acetaldehyde, acetonitrile and isoprene were measured for the first time in the IGP. A new atmospheric chemistry facility that combines India's first highsensitivity proton transfer reaction mass spectrometer, an ambient air quality station and a meteorological station, was used to quantify in situ levels of several VOCs and air pollutants in May 2012 at a suburban site in Mohali (northwest IGP). Westerly winds arriving at high wind speeds (5-20 m s −1 ) in the pre-monsoon season at the site were conducive for chemical characterization of regional emission signatures. Average levels of VOCs and air pollutants in May 2012 ranged from 1.2 to 2.7 nmol mol −1 for aromatic VOCs, 5.9 to 37.5 nmol mol −1 for the oxygenated VOCs, 1.4 nmol mol −1 for acetonitrile, 1.9 nmol mol −1 for isoprene, 567 nmol mol −1 for carbon monoxide, 57.8 nmol mol −1 for ozone, 11.5 nmol mol −1 for nitrogen oxides, 7.3 nmol mol −1 for sulfur dioxide, 104 µg m −3 for PM 2.5 and 276 µg m −3 for PM 10 . By analyzing the one-minute in situ data with meteorological parameters and applying chemical tracers (e.g., acetonitrile for biomass burning) and inter-VOC correlations, we were able to constrain major emission source

Canaliculotomy is safe and efficacious in the treatment of lacrimal canaliculitis with no demonstrable risk of posttreatment epiphora.

Biomass fires impact global atmospheric chemistry. The reactive compounds emitted and formed due to biomass fires drive ozone and organic aerosol formation, affecting both air quality and climate. Direct hydroxyl (OH) Reactivity measurements quantify total gaseous reactive pollutant loadings and comparison with measured compounds yields the fraction of unmeasured compounds. Here, we quantified the magnitude and composition of total OH reactivity in the north-west Indo-Gangetic Plain. More than 120% increase occurred in total OH reactivity (28 s−1 to 64 s−1) and from no missing OH reactivity in the normal summertime air, the missing OH reactivity fraction increased to ~40 % in the post-harvest summertime period influenced by large scale biomass fires highlighting presence of unmeasured compounds. Increased missing OH reactivity between the two summertime periods was associated with increased concentrations of compounds with strong photochemical source such as acetaldehyde, acetone, hydroxyacetone, nitromethane, amides, isocyanic acid and primary emissions of acetonitrile and aromatic compounds. Currently even the most detailed state-of-the art atmospheric chemistry models exclude formamide, acetamide, nitromethane and isocyanic acid and their highly reactive precursor alkylamines (e.g. methylamine, ethylamine, dimethylamine, trimethylamine). For improved understanding of atmospheric chemistry-air quality-climate feedbacks in biomass-fire impacted atmospheric environments, future studies should include these compounds.

Abstract. The TROPOspheric Monitoring Instrument (TROPOMI), launched in October 2017 on board the Sentinel-5 Precursor (S5P) satellite, monitors the composition of the Earth's atmosphere at an unprecedented horizontal resolution as fine as 3.5 × 5.5 km2. This paper assesses the performances of the TROPOMI formaldehyde (HCHO) operational product compared to its predecessor, the OMI (Ozone Monitoring Instrument) HCHO QA4ECV product, at different spatial and temporal scales. The parallel development of the two algorithms favoured the consistency of the products, which facilitates the production of long-term combined time series. The main difference between the two satellite products is related to the use of different cloud algorithms, leading to a positive bias of OMI compared to TROPOMI of up to 30 % in tropical regions. We show that after switching off the explicit correction for cloud effects, the two datasets come into an excellent agreement. For medium to large HCHO vertical columns (larger than 5 × 1015 molec. cm−2) the median bias between OMI and TROPOMI HCHO columns is not larger than 10 % (< 0.4 × 1015 molec. cm−2). For lower columns, OMI observations present a remaining positive bias of about 20 % (< 0.8 × 1015 molec. cm−2) compared to TROPOMI in midlatitude regions. Here, we also use a global network of 18 MAX-DOAS (multi-axis differential optical absorption spectroscopy) instruments to validate both satellite sensors for a large range of HCHO columns. This work complements the study by Vigouroux et al. (2020), where a global FTIR (Fourier transform infrared) network is used to validate the TROPOMI HCHO operational product. Consistent with the FTIR validation study, we find that for elevated HCHO columns, TROPOMI data are systematically low (−25 % for HCHO columns larger than 8 × 1015 molec. cm−2), while no significant bias is found for medium-range column values. We further show that OMI and TROPOMI data present equivalent biases for large HCHO levels. However, TROPOMI significantly improves the precision of the HCHO observations at short temporal scales and for low HCHO columns. We show that compared to OMI, the precision of the TROPOMI HCHO columns is improved by 25 % for individual pixels and by up to a factor of 3 when considering daily averages in 20 km radius circles. The validation precision obtained with daily TROPOMI observations is comparable to the one obtained with monthly OMI observations. To illustrate the improved performances of TROPOMI in capturing weak HCHO signals, we present clear detection of HCHO column enhancements related to shipping emissions in the Indian Ocean. This is achieved by averaging data over a much shorter period (3 months) than required with previous sensors (5 years) and opens new perspectives to study shipping emissions of VOCs (volatile organic compounds) and related atmospheric chemical interactions.

No abstract

O 3 , CO, and NO x affect air quality and tropospheric chemistry but factors that control them in the densely populated N.W. Indo-Gangetic Plain (IGP) are poorly understood. This work presents the first simultaneous 2 year long in situ data set acquired from August 2011 to September 2013 at a N.W. IGP site (30.667°N, 76.729°E; 310 m asl). We investigate the impact of emissions and meteorology on the diel and seasonal variability of O 3 , CO, and NO x . Regional post-harvest crop residue fires contribute majorly to an enhancement of 19 ppb in hourly averaged ozone concentrations under similar meteorological conditions in summer and 7 ppb under conditions of lower radiation during the post monsoon. d [O 3 ]/dt (from sunrise to daytime O 3 maxima) was highest during periods influenced by post-harvest fires in post monsoon season (9.2 ppb h À1 ) and lowest during monsoon season (4.1 ppb h À1 ). Analysis of air mass clusters revealed that enhanced chemical formation of O 3 and not transport was the driver of the summertime and post monsoon ambient O 3 maxima. Despite having high daytime NO x (>12 ppb) and CO (>440 ppb) in winter, average daytime O 3 was less than 40 ppb due to reduced photochemistry and fog. Average daytime O 3 during the monsoon was less than 45 ppb due to washout of precursors and suppressed photochemistry due to cloud cover. The 8 h ambient air quality O 3 standard was violated on 451 days in the period August 2011-September 2013. The results show that substantial mitigation efforts are required to reduce regional O 3 pollution in the N.W. IGP.

No abstract